[Palaeontology, Vol. 55, Part 5, 2012, pp. 1043–1073] OLENEKIAN (EARLY TRIASSIC) BIVALVES FROM THE SALT RANGE AND SURGHAR RANGE, PAKISTAN by MARTIN WASMER 1 , MICHAEL HAUTMANN 1 *, ELKE HERMANN 2 , DAVID WARE 1 , GHAZALA ROOHI 3 , KHALIL UR-REHMAN 3 , AAMIR YASEEN 3 and HUGO BUCHER 1 1 Palaeontological Institute and Museum, University of Zürich, Karl Schmid-Strasse 4, CH-8006 Zürich, Switzerland; e-mails: martin.wasmer@gmail.com, michael.hautmann@pim.uzh.ch, david.ware@pim.uzh.ch, hugo.fr.bucher@pim.uzh.ch 2 Laboratory of Palaeobotany and Palynology, Palaeoecology, Institute of Environmental Biology, Faculty of Science, Utrecht University, Budapestlaan 4, NL-3584 CD Utrecht, The Netherlands; e-mail: elkeschneebeli@gmx.net 3 Pakistan Museum of Natural History, Garden Avenue, Islamabad 44000, Pakistan; e-mails: roohighazala@yahoo.com, reman_geol@yahoo.com, geologistgeologist@yahoo.com *Corresponding author. Typescript received 4 June 2011; accepted in revised form 14 March 2012 Abstract: Based on newly collected material from the unusual genus characterized by a globose shell centre and a strongly plicate fringe. Permophorus costatus, which was previously known exclusively from Permian strata, is reported from the Spathian of the Surghar Range. This record extends the range of P. costatus for at least 8 Myr and makes it the first reported Lazarus species, with an outage of more than 2 Myr after the end-Permian mass extinction. Ten of 15 species recognized in this study have not been reported from other regions, which may indicate increasing provincialism towards the end of the Early Triassic, or, alternatively, reflect the still insufficient knowledge of benthic faunas from the epoch that followed the greatest crisis in the history of life. uppermost Smithian and lower to middle Spathian (Olenekian, Lower Triassic) of the Salt Range and Surghar Range (Pakistan), 15 bivalve species belonging to 11 genera are described, including two new genera, Eobuchia and Dimorphoconcha, and one new species, Palaeoneilo? fortistriata. Eobuchia gen. nov. is placed in a new subfamily, the Eobuchiinae, which differs from the Buchiinae in having an almost planar and only moderately inclined or offset right anterior auricle. Inclination of the right anterior auricle is proposed as a synapomorphy of the revised suborder Monotidina, which includes the Buchiidae, Monotidae, Oxytomidae and, tentatively, the Dolponellidae. The Pseudomonotidae, Chaenocardiidae and Claraiidae are discussed as candidate ancestors of the Monotidina. Dimorphoconcha gen. nov., provisionally placed in the Limidae, is a morphologically Key words: Bivalvia, Monotidina, Lower Triassic, Salt Range, Surghar Range, Pakistan. D espite an increasing interest in the reorganization of marine ecosystems after the end-Permian mass extinction event, only few modern studies have contributed to a systematic census of the Early Triassic fauna and flora. Most of these studies deal with the biostratigraphically most important groups, such as ammonoids (e.g. Brayard et al. 2006, 2007; Brayard and Bucher 2008; Brühwiler et al. 2008; Ware et al. 2011; Brühwiler et al. in press), conodonts (e.g. Orchard 2007; Goudemand et al. in press) and palynomorphs (e.g. Hochuli et al. 2010; Hermann et al. 2011a, 2011b, in press). Benthic groups have been paid less attention, although new taxonomic studies on gastropods (Nützel and Erwin 2002; Pan et al. 2003; Nützel 2005a, b; Kaim 2009; Kaim et al. 2010; Kaim and Nützel 2011) have already significantly improved our knowledge of the recovery of this important class of molluscs. However, the most pronounced mismatch between importance in Early Triassic ecosystems and number of modern taxonomic studies concerns bivalves. Bivalves were the dominant benthic group in the Early Triassic, both in terms of diversity and abundance, but only few recent studies have documented their diversity and taxonomic structure (Newell and Boyd 1995; Dagys and Kanygin 1996; Hautmann and Nützel 2005; Kumagae and Nakazawa 2009; Hautmann et al. 2011, in press). Here, we describe an Early Triassic bivalve fauna from the upper part of the Mianwali Formation of the Salt and Surghar Ranges in Pakistan. The superb record of Late Permian to Early Triassic marine faunas has made this region a key locality for the study of marine invertebrates during the transition from the Palaeozoic to the Mesozoic (Waagen 1879, 1880, 1881, 1882–1884, 1891, 1895; Kummel and ª The Palaeontological Association doi: 10.1111/j.1475-4983.2012.01176.x 1043 1044 PALAEONTOLOGY, VOLUME 55 Teichert 1966, 1970; Guex 1978), but the Early Triassic bivalve fauna from this region has previously been largely ignored. GEOLOGICAL SETTING The Salt and Surghar Ranges in northern Pakistan are situated about 200 km south-west of Islamabad. During the Early Triassic, this area was located at the southern margin of the Tethys, at about 30 degrees south on the northern shelf of Gondwana (Fig. 1; Smith et al. 1994; Golonka and Ford 2000). The Early Triassic sedimentary and palynofacies record of the Salt and Surghar Ranges have recently been studied by Hermann et al. (2011a, b), who provided a synopsis of lithostratigraphy, biostratigraphy and sequence stratigraphy, adopted herein. This study focuses on the upper part of the Mittiwali Member and the lower portion of the Narmia Member (Mianwali Formation) and includes the following lithostratigraphical units, in ascending order: upper part of the Upper Ceratite Limestone (UCL), including the Bivalve Beds (BB); Niveaux Intermédiaires (NI); and lower part of the Topmost Limestone (TL). This roughly corresponds to the period from the latest Smithian to the middle Spathian. The Smithian–Spathian boundary lies within the BB in Nammal, which, however, are diachronous between the Salt Range and Surghar Range (see below). Sedimentologically, the interval studied is characterized by mixed siliciclastic–carbonate deposits that include coquinoid limestone, sandy limestone, sandstone and siltstone (Hermann et al. 2011a). A relatively shallow-marine palaeoenvironment is indicated by sedimentary structures such as karstification and wave ripples in the BB, crossstratification in the NI and Topmost Limestone and by the presence of plant remains. Generally, a slight shallowing upwards trend is observed, especially from the early Spathian onwards. The material studied herein comes from three sections: the Nammal section (Nammal gorge) in the Salt Range and the Landu section (including samples from Chitta gorge, because all beds can be laterally traced between these two approximate localities) and the Narmia section (Narmia gorge) in the Surghar Range (Fig. 1). Lower Triassic strata are slightly thicker in the Surghar Range (130 m) than at Nammal (117 m; Hermann et al. 2011a). All lithological units extend laterally across the Salt and Surghar Ranges and can be precisely correlated by means of ammonoid and conodont biozones and C-isotope data (Hermann et al. 2011a; H. Bucher, N. Goudemand and D. Ware, unpublished data). In the study area, in the lower part of the UCL, limestone beds predominate, intercalated by few sandstone and siltstone beds that occasionally contain fossil-rich limestone lenses. The proportion of siltstone and sandstone increases in the middle portion of the unit, whereas the upper part of the UCL is formed by eight laterally persistent bivalve rudstone beds referred to as ‘Bivalve Beds’ (BB1–BB8; Waagen 1895), which are separated by siliciclastic layers. The d13Ccarb record shows a positive shift in the lowermost bed of the BB at Nammal and Landu (Hermann et al. 2011a), which corresponds to a global isotope signal near the Smithian–Spathian boundary (Payne et al. 2004; Galfetti et al. 2007c). The A B C F I G . 1 . Locality map. A, overview. B, position of Nammal (Salt Range) and Narmia and Landu (Surghar Range) sections. C, palaeogeographical position of the Salt and Surghar Ranges, based on reconstructions by Smith et al. (1994) and Golonka and Ford (2000). WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN topmost bed of the Bivalve Beds (BB8) at Nammal is occasionally karstified and contains intraclasts formed by dissolution. This applies also to the Narmia section, but no signs of karstification have been found in the Landu section. By means of ammonoid faunas, the Smithian UCL can be subdivided into, in ascending order, the Nammalites beds, Prionites beds, Wasatchites–Anasibirites beds and Glyptophiceras beds (Brühwiler et al. 2008, in press). Glyptophiceras occurs c. 2 m below the BB at Nammal and 1.5 m below the BB in the Landu section (Chitta gorge). In the latter section, the first Tirolites occurs c. 9 m above the top of the BB, placing the Smithian–Spathian boundary within a c. 15-m-thick interval between the upper UCL and lower NI. The section at Nammal is much more condensed and stratigraphically notably incomplete. A late Smithian age is indicated by the presence of Hedenstroemia and Xenoceltites between BB2 and BB3, whereas in BB7, a new genus of Tirolitidae that is morphologically transitional towards Columbites already postdates the earliest Spathian. In consequence, at Nammal, the Smithian– Spathian boundary is located above BB3 and below BB7. The fact that no Tirolites was found within this interval suggests a notable incompleteness of the sedimentary record. Similarly, the presence of Procolumbites in BB8 indicates already a middle Spathian age and, thus, an additional sedimentary gap between BB7 and BB8, comprising the Columbites interval. The NI generally consists of siltstone, sandy siltstone and sandstone beds that are 20–30 cm thick on average. Locally, carbonate-cemented pods within the sandstones contain well-preserved fossil material. The Topmost Limestone is a 15-m (Nammal)- to 30-m (Landu)-thick unit that consists of an alternation in siltstone and sandstone beds with several prominent limestone beds in between and especially at the base and top of the unit. The top bed of the Topmost Limestone at Landu is oncolithic and contains rhynchonellid brachiopods. In the sections studied, bivalve shells are usually concentrated within limestone lenses or coquina beds. Virtually all valves are disarticulated, indicating postmortem transportation. However, only few valves are abraded, and no signs of biological alteration after death (e.g. microborings, micritic envelopes) have been observed. In the case of densely packed bivalve rudstones (i.e. BB), in situ concentration and reworking of shells by waves appear likely, whereas in most other cases, the shell concentrations probably represent storm accumulations. A major preservation bias owing to selective dissolution of primary aragonitic shells is unlikely because of the presence of taxa with primary aragonitic shells that are entirely or partially replaced by diagenetic calcite (e.g. Palaeoneilo? fortistriata sp. nov.). 1045 PREVIOUS WORK The Early Triassic bivalve fauna of the Salt and Surghar Ranges is far less well studied than the ammonoid fauna that made this region a classic area for Early Triassic biostratigraphy. Based on material collected by Koken, von Wittenburg (1909) described seven, mostly new, species for the entire Lower Triassic of the Salt Range. Three of these, Pecten (Leptochondria) albertii var. virgalensis, Pecten kokeni sp. nov. and Pseudomonotis punjabensis sp. nov., have been recognized in our material and are discussed below. The remaining four are from the lower part of the Mittiwali Member (Lower Ceratite Limestone to Ceratite Sandstone), which is not covered by the present study. Kummel and Teichert (1970) also mentioned bivalves, but did not describe or illustrated any. Two of these were subsequently listed and illustrated by Newell and Boyd (1995) as Crittendenia kummeli (Newell and Boyd, 1995) and Leptochondria curtocardinalis (Hall and Whitfield, 1877). Both taxa are also recorded by us, the former herein referred to Eobuchia punjabensis. The most recent record of bivalves from the Salt Range is that by Nakazawa (1996), who described material collected by the Pakistani-Japanese research group (PJRG; 1975, 1976 and 1979, mentioned but not described in PJRG 1985). For the interval studied herein (Nakazawa’s units 4 and 5; see Pakistani-Japanese research group 1985), only five taxa were recorded. The taxa described as Claraia (Pseudoclaraia)? nammalensis Nakazawa, 1996, Claraia (Pseudoclaraia) aff. decidens (Bittner, 1901), Claraia? sp. ind. and Scythentolium kokeni (von Wittenburg, 1909) have also been recognized in our material, whereas Modiolus? sp. ind. collected from float, but probably derived from ‘unit 5’ (= Niveaux Intermédiaires), is absent. Nakazawa’s (1996) three species of Claraia are herein tentatively regarded synonymous and assigned to Eobuchia gen. nov. In summary, after elimination of synonyms, only five species have previously been recorded from the interval studied, which is in sharp contrast to the 15 species and 11 genera recognized in this work. MATERIAL AND METHODS Rock samples from the sections discussed above were collected during two field campaigns in 2009 and 2010 by Bucher, Hautmann, Hermann and Ware. The position of samples within the sections is indicated in Figure 2. The samples were mechanically disintegrated, resulting in 0.5– 10 kg of fossiliferous rock fragments per sample. Dominant macrofossils are ammonoids and bivalves, but also brachiopods and gastropods are locally abundant. The bivalve material has been prepared with standard mechanical preparation techniques (by M. Hebeisen and M. Wasmer), where needed. 1046 PALAEONTOLOGY, VOLUME 55 WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN This study focuses on bivalve taxonomy. However, a quantitative analysis involving all complete individuals and fragments representing at least half of the original shell has also been performed. The individual number has been totalled for each species and sample (Fig. 2) by counting the most numerous unarticulated valves for which left ⁄ right orientation was possible, plus half of the large fragments where no orientation was possible, rounded up to entire (Fig. 2). Dominance index was calculated as P ÿni
2 , where n is the number of individuals of D= n taxon i (as used in PAST; Hammer et al. 2001). Other statistical methods have not been adopted because of the relatively low number of specimens and samples. Repository. The material described herein is housed at the Palaeontological Institute and Museum of the University of Zürich, Switzerland (abbreviation: PIMUZ). Nonfigured specimens that were counted for the quantitative analyses but have no inventory numbers are deposited in the stratigraphic collection of the institute. SYSTEMATIC PALAEONTOLOGY by M. Wasmer and M. Hautmann Class BIVALVIA Linnaeus, 1758 Subclass PALAEOTAXODONTA Korobkov, 1954 1047 and five fragments from LAN-B4; three fragments from LAN-B5. (PIMUZ 28674, 28720, 28721, 28851–28858 and unnumbered). Diagnosis. Valves small, subelliptical, moderately to strongly inflated. Umbo broad, beak prosogyrate, at about anterior third of shell length. Shell surface with irregularly spaced commarginal riblets, symmetrical in shape. Resilifer absent. Description. Shell equivalved, inequilateral, subelliptical and prolonged posteriorly, length exceeding height (L ⁄ H ratio c. 1.65, on average), moderately to strongly inflated. Posterior distal end below mid-shell height. Umbo broad, prosogyrate, with beak located about one-third of shell length behind anterior end (e.g. Fig. 3A, B). Irregularly spaced commarginal riblets, symmetrical in cross-section. Adductor muscle scars isomyarian, forming shallow impressions, which are more pronounced dorsally (Fig. 3L, M). Posterior adductor scar ventrally indistinctly passing into a very shallow scar of unknown origin (Fig. 3L, M). Pallial line indistinct, possibly integripalliate (Fig. 3L, M). Hinge taxodont, hinge teeth arranged in two rows meeting below beak. Anterior row with c. nine teeth of similar size, posterior row with c. 30 teeth decreasing in size towards beak (Fig. 3N, O). Resilifer absent, ligament not observed. Shell relatively thick, completely recrystallized. Dimensions. Length between 5 and 10.5 mm (median 8 mm, mean 7.73 mm), height between 4 and 6.5 mm (median 4.5 mm, mean 4.65 mm) (Fig. 4). Order NUCULOIDA Dall, 1889 Superfamily NUCULOIDEA Gray, 1824 Family MALLETIIDAE H. Adams and A. Adams, 1858 Genus PALAEONEILO Hall and Whitfield, 1869 Type species. Nuculites constricta Conrad, 1842. Palaeoneilo? fortistriata Wasmer and Hautmann sp. nov. Figure 3 Holotype. PIMUZ 28851, a left valve from NAM-B8 (Fig. 3A). Derivation of name. Combination of the Latin words fortis for strong and stria for groove, in reference to the ornament. Material. Six left valves, eight right valves and 11 fragments from NAM-B7; 12 left valves, 19 right valves and 23 fragments from NAM-B8; a single left valve and 12 fragments from NAM-B10; two fragments from NAR-B1; one left valve, three right valves and 11 fragments from LAN-B3; six left valves, five right valves Discussion. The variability of the length ⁄ height ratio, convexity and umbonal shape is relatively high, but continuous (Figs 3A–K and 4A). The hinge structure of Palaeoneilo? fortistriata has been analysed in four specimens by means of serial sections (e.g. Fig. 3N). They show a dentition that is similar to that of Palaeoneilo elliptica Goldfuss, 1838 and Prosoleptus lineatus (Goldfuss, 1840). However, in contrast to the latter, a resilifer appears to be absent, although we do wish to note that a minute resilifer as described for P. elliptica by Carter (1990, fig. 12) may be obscured by recrystallization. Externally, the new species differs from other Triassic congeners mainly by its rather oval shape, the comparably strong concentric ornament and the wide umbo. More precisely, P.? fortistriata sp. nov. differs from P. elliptica in the broader and more anteriorly located umbo and in the stronger ornament; from P. praecursor (Frech, 1904) (see also Kiparisova 1938, p. 211, pl. 1, fig. 8a–c) in its continuous and stronger ornament as well as in its slightly broader umbo; from P. faba Wissmann, 1841 Lithology, stratigraphy, positions of samples and distribution of bivalve species in the Nammal (Salt Range), Narmia and Landu (Surghar Range) sections. Basic data on sedimentary structures and additional fossils indicated by pictograms; correlation between sections highlighted by black lines; numbers represent counts of individuals (see text); grey dots indicate tentative assignments. FIG. 2. 1048 PALAEONTOLOGY, VOLUME 55 D C F E G A B H L I M J N K O F I G . 3 . Palaeoneilo? fortistriata sp. nov. A, B, holotype (PIMUZ 28851), left valve from NAM-B8. A, lateral view, ·2. B, dorsal view, ·2. C, PIMUZ 28720, left valve from LAN-B4, ·2. D, PIMUZ 28674, left valve from LAN-B4, ·2. E, PIMUZ 28721, left valve from LAN-B4, ·2. F, PIMUZ 28858, left valve from NAM-B8, ·2. G, PIMUZ 28852, left valve from NAM-B8; shell partially broken away, giving impression of shell thickness, ·2. H, PIMUZ 28857, right valve from NAM-B8, ·2. I, PIMUZ 28856, right valve from NAM-B8, ·2. J, PIMUZ 28855, right valve from NAM-B8, ·2. K, PIMUZ 28854, right valve from NAM-B8, ·2. L–O, internal features, ·4. L, PIMUZ 28853, from NAM-B8, internal view of right valve, showing adductor muscle scars and pallial line. M, same view, with indication of anterior adductor (aa), posterior adductor (pa), pallial line (pl) and muscle scar of unknown origin. N, thin section of right valve, showing anterior and posterior teeth row. O, hinge reconstruction. (= P. tenulineata von Klipstein, 1845; see Bittner 1895), in the broader umbo and generally more oval shape; and from P. sakuradaniensis Ichikawa, 1954 and similar forms from the Lower Triassic of Japan in the more elongated and less trigonal shape, as well as in the prosogyrous beak. Palaeoneilo? fortistriata sp. nov. shows the closest resemblance with P. whitechurchii Healey, 1908 from the Upper Triassic, differing only by its less elongated and more inflated morphology and its slightly stronger commarginal ornament. Triassic Malletiidae of comparable shape, size and ornament have mostly been assigned to Palaeoneilo without consideration of the peculiarities of hinge and ligamental structures of this genus. In Palaeozoic representatives, the posterior teeth row extends above the anterior teeth row (Douvillé 1912, figs 5, 6). Moreover, the Devonian P. filosa Conrad, 1842 has a small trigonal resilifer, symmetrical in both valves, which is ontogenetically superimposed over some hinge teeth (Carter 1990, p. 159, fig. 9). By contrast, the Late Triassic ‘Palaeoneilo’ elliptica as described by Bittner (1895) lacks the overlap of the anterior and posterior teeth rows and possesses a single minute resilifer on the right valve only, the left side of the internal ligament being directly attached to the hinge teeth and sockets (Carter 1990, p. 144). Bittner (1895) reported 15 anterior and up to 50 posterior teeth in ‘P.’ elliptica, both rows merging without interruption. As far as we know, all Triassic species assigned to Palaeoneilo lack overlap of teeth rows, and mostly no resilifer has been observed. Another morphological difference between Palaeozoic and Triassic forms is the absence of a posterior shell constriction in Triassic ‘Palaeoneilo’. Unlike Palaeoneilo, the genus Prosoleptus Beushausen, 1895 has a Triassic type species, Nucula lineata Goldfuss 1833–1840, which has a hinge with c. 10 anterior and c. 30 posterior teeth, both rows merging without interruption; it lacks a resilifer (Bittner 1895, p. 133; Carter 1990, p. 169). The shell microstructure is similar to Triassic ‘Palaeoneilo’, having very homogeneous crossed lamellar structures in the inner and middle shell layers compared with the diffuse structures seen in Palaeozoic species of that genus (Carter 1990, p. 161). However, Prosoleptus possesses a characteristic ventral protrusion, which is absent in Palaeoneilo? fortistriata. Another closely similar genus is the Triassic Phaenodesmia Bittner, 1895, which differs from the above-mentioned taxa by a characteristically tapered posterior shell end. Unfortunately, the description of Phaenodesmia by Bittner (1895) is very rudimentary, and no details of the hinge structure are known, apart from the lack of a resilifer. The comparison of Palaeoneilo, Prosoleptus and Phaenodesmia shows that the Triassic forms are closely related and that Triassic ‘Palaeoneilo’ differs considerably in hinge morphology from the Carboniferous-type species of that genus. In conclusion, there is a strong need for a revision of Triassic Palaeoneilo. Until more details of WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN A 1049 B F I G . 4 . Height and length measurements of Palaeoneilo? fortistriata sp. nov. and Eobuchia punjabensis (von Wittenburg, 1909) comb. nov. A, size scatter diagram for 46 specimens of P.? fortistriata, rounded to 0.5 mm. Numbers in squares indicate counts of individuals with identical size values. B, size scatter diagram for 55 specimens of E. punjabensis, rounded to 1 mm. Size of slightly incomplete individuals estimated. hinge and ligament are known, we refrain from making our new species the type of a new genus. Occurrence. Pakistan, Spathian (BB, NI, Topmost Limestone) in all sections studied. Palaeoecology. An infaunal deposit feeder; it is debatable whether the trophic mode of infaunal deposit feeders might be less sensitive to environmental perturbations than that of suspensionfeeding groups (Sheehan and Hansen 1986; Levinton 1996). Subclass PTERIOMORPHIA Beurlen, 1944 Order PTERIOIDA Newell, 1965 Suborder PTERIINA Newell, 1965 Superfamily PINNOIDEA Leach, 1819 Family PINNIDAE Leach, 1819 Genus PINNA Linnaeus, 1758 Type species. Pinna rudis Linnaeus, 1758. Pinna muikadanensis Nakazawa, 1961 Figure 5A * 1961 Pinna muikadanensis Nakazawa, p. 267, pl. 13, figs 14–17. Material. A single right valve (PIMUZ 28671) from NAM-B9. Description. Valve triangular in outline, apical angle c. 35 degrees, weakly inflated, with weak median ridge distally extending into fracture of shell. Ornament of radial ribs, distally increasing in number by intercalation, effacing near beak. About 10 ribs ventrally of median ridge, weavy and more closely spaced than on dorsal part of valve; seven ribs on dorsal part of valve, distally increasing up to at least 14 ribs (incomplete valve) by intercalation. Growth lines ventrally curved, dorsally nearly straight and perpendicular to dorsal margin, slightly weaker than on ventral side. Dorsal shell margin thickened, showing prismatic structure. Small bulgy structures projecting into shell cavity near tip of umbo on ventral side. One strong growth irregularity proximally, at which radial ribs are set off, and three weaker irregularities distally at which only half of the ribs, dorsally or ventrally of the median ridge, are dislocated. Dimensions. Length >34 mm, height >15 mm (incomplete). Discussion. Shape and ornament are comparable to Pinna muikadanensis. Our specimen differs from the type material of Nakazawa (1961, p. 267, pl. 13, figs 14–17) only by its smaller size and slightly weaker radial ornament. The fragment of Pinna sp. ind. described by Yehara (1927, p. 171, pl. 16, fig. 17) from the Lower Triassic of Japan differs from P. muikadanensis by more widely spaced, coarser ribs, as well as by the lack of visible growth lines. Waller and Stanley (2005, p. 29) discussed morphological differences and stratigraphical ranges of the genera Pinna and Atrina Gray, 1842. They suggested that, contrary to Cox and Hertlein (in Cox et al. 1969, p. N297), 1050 PALAEONTOLOGY, VOLUME 55 A B mann (2001b) described well-preserved specimens of Pinna from the Upper Triassic of the Nayband Formation with well-visible carinae, thus expanding the first occurrence of the genus to the Late Triassic. In the present specimen, a median ridge along the line of maximum shell inflation is observed, which distally extends into a zone where the ventral and dorsal parts of the shell have been disrupted. Nakazawa (1961, p. 267) described the presence of a ‘median parting distinct but weak in the umbonal half and obsolete in the rear half’ in P. muikadanensis, which probably corresponds to the median ridge in our specimen. Judging from Nakazawa’s illustration (1961, pl. 13, fig. 14), this median parting extends over two-thirds of the shell length and is thus clearly not restricted to the juvenile shell. Based on these observations, we assign our specimen to Pinna rather than to Atrina, implying that Pinna might have evolved soon after the end-Permian mass extinction. The small bulgy structures ventrally near the umbo may represent remnants of septae inserted in response to the displacement of the anterior adductor muscle during shell growth (Hautmann 2001b, p. 60). The prismatic structure at the dorsal margin could represent a part of the outer shell layer or of the fibrous ligament. Occurrence. Southern Japan, Olenekian (Yakuno Group; lower Oro Formation and Kusano Formation) and Pakistan, Spathian (NI) of the Nammal section. Palaeoecology. Semi-infaunal filter feeder, byssally attached (e.g. Fürsich 1980). Superfamily PTERIOIDEA Gray, 1847 Family BAKEVELLIIDAE King, 1850 Genus BAKEVELLIA King, 1848 C A, Pinna muikadanensis Nakazawa, 1961 (PIMUZ 28671), right valve from NAM-B9; ca: median ridge tentatively interpreted as carina; pr: prismatic layer along the dorsal shell margin; ·2. B, C, Bakevellia? sp. nov. B, PIMUZ 28673, right valve from NAM-B7; note small, pointed anterior wing and decrease of shell thickness from proximal to distal; pa: posterior adductor muscle scar; pl: pallial line; ·2.5. C, PIMUZ 28672, internal mould of right valve with partly adhering shell, from NAM-B7; note small, pointed anterior wing; ·2.5. FIG. 5. the latter was the stratigraphically older genus, which agrees with its more primitive morphology (i.e. lack of median carina and corresponding zone of shell flexure). Turner and Rosewater (1958) indicated that Pinna first appeared in the Jurassic, a view that was implicitly adopted by Waller and Stanley (2005). However, Haut- Type species. Avicula antiqua von Münster in Goldfuss, 1836 (non Avicula antiqua Defrance 1816; = Avicula binneyi Brown, 1841). Bakevellia? sp. nov. Figure 5B, C Material. Two incompletely preserved right valves from NAMB7 (PIMUZ 28672, 28673); two tentatively assigned fragments of left valves from NAM-B5. Description. Right valve subtrapezoidal, moderately inflated, retrocrescent, angle between dorsal margin and line of maximum inflation about 130 degrees. Dorsal margin long and straight. Beak at the anterior one-third of dorsal margin. Umbo prominent, prosogyrous; beak slightly protruding above dorsal margin. Anterior wing very small and acute, anterior margin rounded WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN (Fig. 5B). Preserved part of posterior wing large and flat. No ornament except for growth lines. Posterior adductor muscle scar large, pallial line integripalliate (Fig. 5B). Shell completely recrystallized, thick near umbo, thin ventrally. Hinge details unknown. Left valve not observed. Dimensions. PIMUZ 28672, length >19 mm (incomplete), height 18 mm; PIMUZ 28673, length >24 mm (incomplete), height 21 mm. Discussion. The families Bakevellidae, Cassanellidae Ichikawa, 1958 and Pteriidae Gray, 1847 encompass forms that are often difficult to distinguish on the basis of external morphology alone (e.g. Tëmkin and Pojeta 2010). Within bakevellids, variability in musculature, hinge dentition and ligament is also considerable (e.g. Muster 1995, p. 4), leading to speculations that the family as currently understood is polyphyletic (e.g. Cox et al. 1969, p. N306). Thus, a revision of these pteriiform families is needed (e.g. Boyd and Newell 2002, p. 2). We tentatively attribute our material to Bakevellia on account of the fact that external morphology resembles certain Early Triassic species assigned to that genus. The most closely similar species is Bakevellia okuyamensis Nakazawa, 1959 and allied forms from the Lower Triassic of Japan, which agree in having a well-inflated right valve with a beak that slightly projects above the dorsal margin. Differences include the much larger size of our material and the presence of an acute anterior wing, which appears blunt in the reconstructions of B. okuyamensis by Nakazawa (1959). Bakevellia exporrecta (Lepsius, 1878) and B. binneyi (Brown, 1841) differ from B. okuyamensis in having a commonly less inflated right valve with an umbo that does not project above the dorsal margin, in being more retrocrescent and, lastly, in having a blunt anterior auricle. Pteria ussurica (Kiparisova, 1938) from the Lower Triassic of the Russian Far East differs externally from our material by a less inflated right valve and more extended wings (compare Kumagae and Nakazawa 2009, pp. 158–160, fig. 144.6–8). Occurrence. Pakistan, latest Smithian? to Spathian (BB) of the Nammal section. Palaeoecology. Endobyssate filter feeder (Stanley 1972; Muster 1995). Order PECTINOIDA Gray, 1854 Suborder MONOTIDINA Waterhouse, 2001 emend Emended diagnosis. Pectinoids with small, but distinct right anterior auricle, which is inclined or offset towards the left valve, and with a tendency towards reduction of the anterior part of the alivincular ligament. 1051 Included families. Buchiidae Cox, 1953, Monotidae Fisher, 1887, Oxytomidae Ichikawa, 1958 and, tentatively, Dolponellidae Waterhouse, 2001. No superfamily arrangement is presently proposed. Discussion. The taxonomy and phylogenetic relationships of the families united herein in the emended suborder Monotidina are controversial (e.g. Ichikawa 1958; Waller 1978; Begg and Campbell 1985; Sha and Fürsich 1994; Carter 1990; Carter et al. 1998; Waterhouse 2008). Waterhouse (2001) united the Eurydesmidae Reed, 1932, Buchiidae, Monotidae and Dolponellidae in the Monotidina, based on the following shared characters: retrocrescent (erroneously procrescent in Waterhouse 2008, p. 109) and often inequivalved shells, monomyarian musculature, largely ophisthodetic ligaments and an anterior auricle that, if present, is located in front of and below the ligament (Waterhouse 2008, p. 109). In his discussion, Waterhouse (2008, p. 110) detailed that the ligament in the Monotidina was often ‘truncavincular’, that is, the ligament did not extend anteriorly to the umbo and that a resilifer, if present, was situated at the anterior edge of the ligament system, implying reduction of the anterior bourrelet. Indeed, most buchiids possess ligament areas largely situated posteriorly to their umbones. However, this does not apply to the Dolponellidae, which were also included in the Monotidina by Waterhouse (2008). Moreover, the ligament morphology in the Eurydesmidae is highly variable and not always in accordance with the original diagnosis of the Monotidina. It is mostly opisthodetic transitional (sensu Newell and Boyd 1987, 1995), but a right valve of Eurydesma cordatum illustrated by Waterhouse (1980, fig. 6) does show an amphidetic ligament area with a central resilifer. The bourrelets in this particular specimen are asymmetrical, with a larger posterior part and a short, bulge-like anterior. The latter was interpreted as an incipient auricle by Waterhouse (1980), but it rather resembles the arched bourrelets that occur in the left valves of oysters (Hautmann 2004, 2006). In summary, a taxonomy based on ligament morphology alone would confine the Monotidina to the Monotidae (excluding the Otapirinae) and Buchiidae, with problematic exceptions, for example the genera Marwickiella, Aucellina and Malayomaorica, some of which Waterhouse (2001; compare Waterhouse 2008) consistently moved to other (sub)families (e.g. Aucellinae Waterhouse, 2001). We propose that the shared presence of a small, but distinct right anterior auricle that is inclined or offset (e.g. in Etalia Begg and Campbell, 1985) towards the left valve is synapomorphic for a revised suborder Monotidina, which excludes the Eurydesmidae but to which the Oxytomidae are added. Functionally, the peculiar orienta- 1052 PALAEONTOLOGY, VOLUME 55 tion of the right anterior auricle might have served for supporting hinge articulation and for widening the gap for byssus extrusion. Other shared characters include inequivalved shells with less inflated right valves and retrocrescent discs in most groups. The ligament is alivincular-external with a prosocline resilifer and shows a tendency towards shortening (oxytomids; e.g. Begg and Campbell 1985, fig. 8) or reduction (most genera of the Buchiidae and Monotidae; e.g. Sha and Fürsich 1994) of the anterior bourrelet. A close relationship between the families herein united in the Monotidina has also been suggested on the basis of shell microstructural similarities, with a predominance of foliated calcite (Waller 1978; Carter 1990; Carter et al. 1998). The monospecific family Dolponellidae from the Permian is tentatively assigned to the Monotidina, because its sole representative, Dolponella sulcata Waterhouse, 1978, has an inclined right anterior auricle (Waterhouse 2008, p. 128) that is suggestive of the Monotidina. The general shape and the presence of a prominent posterior-lateral sulcus are reminiscent of Pseudomonotis Beyrich, 1862. However, Waterhouse (1978, p. 104) indicated the presence of an external ligament area that has faint vertical and longitudinal striae and lacks a distinct resilifer (‘platyvincular’ ligament in Waterhouse 2008, pp. 10, 128), which distinguishes it from Pseudomonotis and the Monotidina. In spite of this difference, we regard the Dolponellidae as a possible phylogenetic link between the Monotidina and Pseudomonotidae (see below). We include the Otapirinae Waterhouse, 1982 in the Monotidae because of the striking morphological similarities, in spite of a larger, more symmetrical alivincular amphidetic ligament and a more strongly developed resilifer in the genus Otapiria Marwick, 1935 (see Begg and Campbell 1985, pp. 736, 737, fig. 8). The emended diagnosis presented above avoids the problem of transferring well-established buchiid genera to other families, but it thereby leads to an alteration of the scope of the Monotidina, with removal of the Eurydesmidae and the addition of the Oxytomidae. The revised composition is essentially identical to Waller’s (1978, p. 362) ‘Buchiacea’, proposed mainly on the basis of shell microstructural characters, except of the Pseudomonitidae which, however, represent a candidate ancestor. We currently do not propose superfamilies within the Monotidina because details of the internal morphology are insufficiently known in many families. Family BUCHIIDAE Cox, 1953 Subfamily EOBUCHIINAE subfam. nov. Diagnosis. Buchiids with an almost planar, small, slender and moderately inclined or offset right anterior auricle. Included genera. Eobuchia gen. nov. and Etalia Begg and Campbell, 1985. Discussion. Members of the new subfamily differ from other buchiids in having almost planar, small and slender spatulate or linguiform auricles that are only slightly inclined or offset towards the left valve. They have not yet evolved dorsally reinforced, spoon-shaped or concave right anterior auricles, as in later buchiids (e.g. Hokonuia Trechmann, 1918; Malayomaorica Jeletzky, 1963), and do not possess auricles that strongly protrude towards the left valve (as in e.g. Marwickiella Sha and Fürsich, 1994). Being basal taxa with a distinct morphology, grouping them in this new subfamily appears warranted. Genus EOBUCHIA gen. nov. Type species. Pseudomonotis punjabensis von Wittenburg, 1909. Derivation of name. A combination of the Greek word ‘eo’ for early and the genus name Buchia. Diagnosis. Valves suboval in outline, retrocrescent, height slightly exceeding length. Left valve moderately to strongly inflated, umbo prominent, beak projecting beyond dorsal margin. Right valve weakly inflated, umbo lower than in opposite valve but still projecting hinge margin. Tiny, spatulate and almost planar right anterior auricle slightly inclined anterodorsally towards the opposite valve. Subauricular notch deep, anterodorsal shell margin slightly arched. Surface of both valves occasionally with commarginal folds and often with well-visible growth rugae. Occasionally faint radial striations on left valves. Discussion. We place the new genus in the Buchiidae because it agrees with this family in a retrocrescent shell, an oblique-ovate valve outline, absence of strong ornament, inequivalved condition with a more inflated left valve in which the umbo protrudes higher than in the opposite valve, short hinge line and most importantly, presence of a tiny, slightly inclined right anterior auricle with a deep subumbonal notch. In more advanced buchiids, this auricle is often dorsally reinforced and strongly tilted towards the opposite valve where it articulates with a characteristic socket (‘Gelenkgrube’of Pompeckj 1901 and later authors). As outlined above, we assign Eobuchia gen. nov. to a new subfamily based on this distinction from more advanced buchiids. The genus Etalia from the Middle Triassic (Anisian) of New Zealand is similar to Eobuchia gen. nov. in the shape of the left valve, but differs in having a flat or concave, occasionally procrescent right valve (Begg and Campbell 1985, fig. 3c, d) with a proportionally larger anterior auricle. WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN This auricle is not inclined as in Eobuchia gen. nov., but slightly offset towards the left valve (Begg and Campbell 1985, p. 729). Moreover, Etalia johnstoni has a rudimentary right posterior auricle (Begg and Campbell 1985, p. 729, fig. 3a, b, f, l), unlike Eobuchia gen. nov. Etalia was referred to the family Asoellidae Begg and Campbell, 1985, which is characterized by ‘alivincular amphidetic ligament areas with a subumbonal triangular resilifer and a right anterior auricle that is often almost planar and variably developed’ (Begg and Campbell 1985, p. 727). In view of the fact that asoellids have been defined solely on the basis of these plesiomorphic characters, there is no clear evidence for phylogenetic links between the genera united in this family, including Etalia. We assign Etalia to the Buchiidae (subfamily Eobuchiinae n. subfam.), based on the morphology of the right anterior auricle and its overall similarity to Eobuchia gen. nov. The hinge and ligament of Eobuchia gen. nov. are unknown; however, Etalia differs from all later buchiids in having a more symmetrical and more anteriorly extending ligament (Begg and Campbell 1985, p. 729, fig. 4). This difference in the ligament structure and the rudimentary right posterior auricle distinguishes Etalia from other members of the Buchiidae and indicates a basal position of this genus within this family. Marwickiella Sha and Fürsich, 1994 was erected for Sichuania? marwicki Waterhouse, 1980, which was originally described as a buchiid lacking a right anterior auricle. Based on additional material of S.? marwicki from the type locality, Begg and Campbell (1985, p. 738, fig. 8l) demonstrated the presence of a strongly inclined right anterior auricle, which protruded into the umbonal cavity of the left valve. We follow Sha and Fürsich (1994, p. 21), who introduced the new buchiid genus Marwickiella (with S.? marwicki as type species), and excluded Sichuania Chen in Gu et al., 1976 from the Buchiidae because of the absence of such an auricle. The minute and strongly inclined auricle of Marwickiella is indicative of the Buchiidae sensu stricto rather than the Eobuchiinae subfam. nov. Apart from this difference, Marwickiella is also distinguished from Eobuchia gen. nov. by a less inflated right valve with an ‘inconspicuous umbo’ (Waterhouse 1980, p. 5) that does not project above the dorsal shell margin. Another Triassic buchiid genus is Hokonuia Trechmann, 1918 from the Carnian of New Zealand. Based on descriptions by Marwick (1953) and Waterhouse (1960), Hokonuia differs from Eobuchia gen. nov. in having a broad and anterodorsally reinforced auricle, a wide subauricular notch and a ctenolium. Further differences include the broader shape, a more extended and flattened anterior wing, stronger prosogyrate beaks and a larger average size. Left valves of the Early Triassic Crittendenia Newell and Boyd, 1995 are morphologically almost identical to those 1053 of Eobuchia gen. nov., differing only in being less retrocrescent. When erecting Crittendenia, Newell and Boyd (1995, fig. 39) indeed identified left valves of Eobuchia punjabensis (von Wittenburg, 1909) from the Mittiwali Member of the Salt Range as Crittendenia kummeli Newell and Boyd, 1995, a species from the western USA. However, unlike Eobuchia gen. nov., the right valve of Crittendenia has a strongly prosogyrate umbo and a very wide byssal notch below the anterior auricle, formed by a conspicuous ventral offset of the shell margin below and in front of the anterior auricle (e.g. Newell and Boyd 1995, fig. 38.8). Tight byssal fixation in Crittendenia is indicated by the general presence of a xenomorphic area (cicatrix) near the beak of the right valve (Newell and Boyd 1995), a feature that has not been observed in Eobuchia gen. nov. The right anterior auricle of Crittendinia additionally differs from that of Eobuchia gen. nov. in bearing radial ribs (Newell and Boyd 1995, fig. 38.8). A possible inclination ⁄ offset of this auricle has not been described. Newell and Boyd (1995, p. 52) proposed that Crittendenia embraced the ‘Claraia decidens’ group of Ichikawa (1958), but they noted, without further explanation, that ‘decidens is significantly unlike […] Claraia’ and assigned Crittendenia tentatively to the Deltopectinidae Dickins, 1957, based on external similarities with Streblopteria M’Coy, 1851. A revision of Crittendenia is beyond the scope of this study, but we do wish to note that assignment of the different species of the decidens group to either Crittendenia or Eobuchia gen. nov. requires data on the morphology of the right valve, which is mostly not available. Contrary to Newell and Boyd (1995), we do not reject possible derivation of Crittendenia from Claraia Bittner, 1901 on the basis of the available morphological data either. The most important differences between these genera are a broader byssal notch in the right valve of Crittendenia and a more convex left valve. However, the form of the byssal notch is highly variable in Claraia, which includes a slitlike, distally contracted type (‘Pseudoclaraia type’) and subcircular structures (‘Claraioides type’), the taxonomic significance of which is still being discussed (e.g. He et al. 2007; Fang 2010). The ventral offset of the shell margin below and in front of the anterior auricle that forms the wide byssal notch in Crittendenia possibly represents another variation of this theme. The right valve of Claraia resembles that of Eobuchia gen. nov. in having a small anterior auricle, but it differs in the lack of inclination or offset of this auricle and in the frequently observed presence of a cicatrix in its umbonal region (Ichikawa 1958), as in Crittendenia. Left valves of Claraia are similar to those of Eobuchia gen. nov. in outline, but are less convex and usually length exceeds height. Stratigraphically, Eobuchia gen. nov. is the oldest genus of the Buchiidae. Waterhouse (1980) described Marwickiella 1054 PALAEONTOLOGY, VOLUME 55 marwicki (Waterhouse, 1980) from the ‘Early Triassic’ of New Zealand, but Begg and Campbell (1985, p. 738) pointed out that this material actually was early Middle Triassic in age, over which, in turn, Waterhouse (2008, p. 127) expressed doubts. The early appearance of Eobuchia gen. nov. puts important constraints on the spectrum of possible ancestors of the Buchiidae, because it excludes several candidate ancestors such as the Jurassic oxytomid Meleagrinella Whitfield, 1885 (see Pompeckj 1901) or the Late Triassic monotid Otapiria (see Zakharov 1981). Having excluded post-Early Triassic taxa as possible ancestors, essentially three candidate phylogenetic lineages leading to the Buchiidae remain. The first is a lineage from the Pennsylvanian–Permian Pseudomonotis via the morphologically similar Permian genus Dolponella to Eobuchia gen. nov. (see above). This lineage is supported by consecutive stratigraphical appearance of these genera and the great morphological similarity between Pseudomonotis and the possible monotidine genus Dolponella (Waterhouse 2008). However, Dolponella is morphologically distant from other Monotidina in having a pronounced sulcus in its left valve, leaving open the possiblity that the inclination of its anterior auricle evolved convergently to the Buchiidae. Alternative phylogenies include a descent from the Chaenocardiidae Miller, 1889, as was implied by Newell and Boyd (1995) when they placed this family in the Monotoidea. According to those authors (Newell and Boyd 1995, p. 76), the Chaenocardiidae share with the Monotoidea the usually obliquely oval shell form, the lack of posterior auricles, the virtually unornamented shell exterior, a commonly calcitic shell with crossed foliated microstructure and the transitional, usually opisthodetic, ligament. Chaenocardiids (excluding Eurydesma, see below) thus appear as a possible ancestral group, although there is a comparatively extensive stratigraphical gap between the youngest chaenocardiids (Early Permian) and the first buchiids. Waterhouse (2008, fig. 111) suggested a link with the Eurydesmidae, which he included in his Monotidina. This, however, appears less likely because Eurydesma Morris, 1845 lacks a clearly differentiated right anterior auricle. The ‘projecting anterior ear ledge’ of Waterhouse (2008) most likely represents an articulating structure that is not homologous to the right anterior auricle in the Monotidina. A third possible phylogenetic lineage leads from Claraia via Crittendenia to Eobuchia gen. nov. Morphological differences between these genera are relatively small (see above), and the stratigraphical appearance of the genera is perfectly consecutive: Claraia sensu lato first appears in the Wuchiapingian (Late Permian; Fang 2010), reaches its acme in the Induan and vanishes at the beginning or during the Olenekian (Nakazawa 1977; note that poor preservation makes most Olenekian records uncertain). The type species of Crittendenia is of early Olenekian age (Meekoceras graciliatis Zone, middle Smithian; Jenks et al. 2010), followed by the late Smithian to Spathian Eobuchia gen. nov. This lineage, if confirmed, implies that the Permian Dolponella evolved the inclination of the anterior auricle convergently and thus should be excluded from the Monotidina. However, data on internal shell characters are needed to test the different phylogenetic pathways that are compatible with data on external shell morphology. Eobuchia punjabensis (von Wittenburg, 1909) Figure 6A–U *1909 Pseudomonotis punjabensis von Wittenburg, p. 11, pl. 3, fig. 3 a, b. ?p 1995 Crittendenia kummeli Newell and Boyd, fig. 39.1–3, [non fig. 38 = Crittendenia kummeli Newell and Boyd, 1995]. 1996 Claraia (Pseudoclaraia)? nammalensis Nakazawa, p. 226, pl. 2, figs N, O, ?P. 1996 Claraia sp. aff. decidens Bittner, 1899; Nakazawa, pp. 225, 226, pl. 2, figs K, L. 1996 Claraia? sp. ind. Nakazawa, pp. 226, 227, pl. 2, figs R, S. A–U. Eobuchia punjabensis (von Wittenburg, 1909) comb. nov. A, PIMUZ 28676, internal mould of left valve from NAMB9, ·2. B, PIMUZ 28677, internal mould with partially preserved thin shell material, LAN-B3, ·2. C–F, reconstruction of Eobuchia punjabensis, c. ·1. C, left valve, dorsal view. D, right valve, dorsal view. E, left valve, exterior. F, right valve, exterior. Note morphology and orientation of right anterior auricle. G, PIMUZ 28679, left valve from NAM-B9, ·2. H, PIMUZ 28680, left valve from NAM-B9, ·2. Note delicate radial ribs. I, PIMUZ 28682, right valve from LAN-B3, ·2. J, K, PIMUZ 28684, right valve from NAM-B9; J, view of complete valve, ·2; K, details of auricle and dorsal margin, ·4. L, M, PIMUZ 28685, right valve from LAN-B3. Note partially preserved thin shell material. L, view of complete valve, ·2. Note internal radial furrows. M, details of auricle and dorsal margin, ·4. N, O, PIMUZ 28683, right valve from LAN-B3. N, view of complete valve ·2. Anterior part of dorsal shell margin broken and displaced; small anterior auricle partly preserved. O, details of anterior auricle and posterior dorsal margin, ·4. Distal part of auricle incomplete. P, Q, PIMUZ 28686, internal mould of right valve from NAM-B9. P, view of complete valve, ·2. Q, details of auricle, ·4. R, PIMUZ 28688, internal mould of juvenile right valve from NAM-B9, ·4. S, PIMUZ 28687, juvenile right valve from LAN-B3, ·4. T, U, PIMUZ 28691, internal mould of juvenile right valve from NAM-B9. T, view of complete valve, ·2. U, details of auricle and dorsal margin, ·4. V, W. Eobuchia? sp. nov. V, PIMUZ 28715, left valve from LAN-B6, ·2. Note partially preserved outer shell layer. W, PIMUZ 28716, left valve from LAN-B6, ·2. Note partially preserved outer shell layer. FIG. 6. WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN C D E F 1055 B A I H G J P L N M O K Q R T W V S U 1056 PALAEONTOLOGY, VOLUME 55 Material. Thirteen left valves, 17 right valves and nine fragments from NAM-B9; 14 left and 11 right valves from LAN-B3. Description. Shell thin, inequivalve, retrocrescent. Valves suboval in outline, with slightly variable shape. Dorsal margin short, angle between anterior and posterior dorsal margin c. 140 degrees. Left valve well inflated, with prominent, virtually orthogyrate umbo projecting beyond dorsal margin. Right valve convex, but less inflated than left valve. Umbo small, nearly orthogyrate, slightly projecting beyond dorsal margin. Anterodorsal shell margin slightly gaping towards plane of commissure (Fig. 6D). Tiny spatulate anterior auricle, proportionally larger in juveniles (Fig. 6R–U), anterodorsally inclined towards commissural plane, externally with well-visible commarginal growth lines (Fig. 6K, M). Subauricular notch moderately wide and deep. Shell surface of both valves occasionally with commarginal folds (Fig. 6N), in left valves additionally with faint radial striations. Growth lines faint, distally usually more pronounced. Traces of three or more internal radial ridges observed on various internal moulds, starting near umbo, enclosing c. 15 degrees between each other (Fig. 6L). Hinge and ligament structures not observed. Dimensions. Length from 4 to 35 mm (median 17 mm, mean 16.7 mm), height from 4 to 35 mm (median 18 mm, mean 17.9 mm) (Fig. 4B). Discussion. von Wittenburg (1909) erected Pseudomonotis punjabensis on the basis of several left valves, only one of which was illustrated (von Wittenburg 1909, pl. 3, fig. 3a, b), from the ‘zone of Stephanites superbus (= Upper Ceratite Limestone; see Nakazawa 1996) of Chideru (= Chhidru)’ in the Salt Range. Re-examination of von Wittenburg’s type material has shown that his drawing of P. punjabensis (von Wittenburg 1909, pl. 3, fig. 3a, b) is inaccurate (R. Hofmann, pers. comm., 2010). In fact, this left valve is virtually indistinguishable from left valves in our material. Despite the lack of right valves in von Wittenburg’s (1909) material, the similarity of the left valves and the fact that both species stem from the same region and stratigraphically adjacent units justify treatment of our material as conspecific. Claraia (Pseudoclaraia?) nammalensis Nakazawa, 1996 and Claraia sp. aff. decidens Bittner, 1899 as described by Nakazawa (1996) from the NI of Nammal are probably conspecific with E. punjabensis. The left valves illustrated by Nakazawa (1996, pl. 2, figs K, L, N, O) are morphologically indistinguishable from our material. The right valve of C. (Pseudoclaraia)? nammalensis illustrated by Nakazawa (1996, pl. 2, fig. O) is not complete, but the umbonal region and the right anterior auricle are similar to those in E. punjabensis and could be conspecific. We also assume that Newell and Boyd (1995, fig. 39.1–3) erroneously assigned a collection of left valves of E. punjabensis from the UCL of Nammal (from bed 25 in Kummel 1966, p. 410) to their new taxon Crittendenia kummeli. Occurrence. Pakistan, Smithian of the Chhidru and Nammal sections and Spathian of the Nammal and Narmia sections (von Wittenburg 1909; Nakazawa 1996); Spathian (NI) of the Nammal and Landu sections. Palaeoecology. We infer an epibyssate mode of life, pleurothetically resting on the right valve, based on the presence of a byssal notch ⁄ gap in that valve and its lesser inflation. Eobuchia? sp. nov. Figure 6V, W Material. Two left valves (PIMUZ 28715 and 28716) from LAN-B6. Description. Left valve posteriorly expanded, with prolonged and nearly straight dorsal margin. Shell exterior with irregularly spaced growth rugae. Shell exterior with some commarginal folds. Right valve and details of shell interior unknown. Dimensions. PIMUZ 28715, length 2.4 mm, height >1.5 mm (incomplete); PIMUZ 28716, length 2.1 mm, height >1.2 mm (incomplete). Discussion. The left valve is similar to that of Eobuchia punjabensis in its retrocrescent shape, prominent umbo and ornament. The principal difference is the prolonged dorsal margin, which makes the generic assignment uncertain. Occurrence. Pakistan, Spathian (Topmost Limestone) of the Landu section. Palaeoecology. Probably epibyssate–pleurothetic in analogy to E. punjabensis. Suborder PECTININA Waller, 1978 Superfamily AVICULOPECTINOIDEA Meek and Hayden, 1864 Family ASOELLIDAE Begg and Campbell, 1985 Remarks. We follow Hautmann et al. (in press) in regarding the Leptochondriidae Newell and Boyd, 1995 (p. 69) to be a younger synonym of the Asoellidae. Genus LEPTOCHONDRIA Bittner, 1891 Remarks. Our material includes only left valves. The absence of right valves is probably due to weak calcification (Newell and Boyd 1995, p. 69). Leptochondria cf. curtocardinalis (Hall and Whitfield, 1877) Figure 7A–C * 1877 Aviculopecten curtocardinalis Hall and Whitfield, p. 273, pl. 6, fig. 4. WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN 1057 D E C B A G F M L I H J K O P N Q R S T U V W A–C, Leptochondria cf. curtocardinalis (Hall and Whitfield, 1877); all specimens from NAR-B1. A, PIMUZ 28693, left valve, ·2. B, PIMUZ 28692, left valve, ·2. Note slightly sinuate posterior auricle. C, PIMUZ 28694, left valve, ·2. Note slightly sinuate posterior auricle. D–J, Leptochondria xijinwulanensis Sha, 1995; all specimens from LAN-B6. D, PIMUZ 28698, left valve, ·2. E, PIMUZ 28702, left valve, ·2. F, PIMUZ 28700, left valve, ·2. G, PIMUZ 28701, left valve, ·2. H, PIMUZ 28699, left valve, ·2. I, PIMUZ 28704, internal mould of left valve, ·2. J, PIMUZ 28703, juvenile left valve, ·2. K–R, Leptochondria viezzenensis (Wilckens, 1909). K, PIMUZ 28705, left valve from NAM-B9, ·2. Note sinuate posterior auricle and long dorsal margin. L, PIMUZ 28689, left valve from NAM-B9, ·2. M, PIMUZ 28690, left valve from NAM-B9, ·2. N, PIMUZ 28678, left valve from LAN-B3, ·2. Note large size. Posterior auricle damaged. O, PIMUZ 28707, left valve from NAM-B8, ·2. P, PIMUZ 28706, left valve from NAM-B8, ·2. Q, PIMUZ 28709, left valve from LAN-B4, ·2. Specimen tentatively attributed to this species. R, PIMUZ 28708, juvenile left valve from NAM-B9, ·2. Note sinuate posterior auricle and juvenile shape; posterior auricle damaged. S–W. Leptochondria virgalensis (von Wittenburg, 1909). S, PIMUZ 28710, left valve from LAN-B1, ·2. T, PIMUZ 28713, left valve from LAN-B1, ·2. U, PIMUZ 28711, left valve from LAN-B1, ·2. Note about a dozen more prominent ribs. V, PIMUZ 28714, left valve from NAM-B3, ·2. W, PIMUZ 28712, left valve from LAN-B1, ·2. FIG. 7. 1058 PALAEONTOLOGY, VOLUME 55 1963 Monotis? thaynesiana (Girty, 1927); Ciriacks, p. 81, pl. 15, fig. 16. 1963 Monotis? landerensis (Branson, 1930); Ciriacks, p. 51, pl. 6, fig. 8. 1995 Leptochondria curtocardinalis Hall and Whitfield; Newell and Boyd, p. 69, fig. 1.1, 2 (with synonymy). Material. Three left valves (PIMUZ 28692–28694) from NAR-B1. Description. Left valve subcircular, infracrescent (Fig. 7A) to slightly procrescent (Fig. 7B), weakly inflated. Umbo orthogyrate, beak low, not projecting above short and straight dorsal margin. Position of beak near or slightly behind centre of dorsal margin. Anterior auricle not clearly delimited, its anterior margin forming an obtuse angle with dorsal margin. Posterior auricle subtriangular with weak sinus ending slightly pointed at dorsal margin. Ornament consisting of very fine and close-set radial ribs, ventrally intercalating in three or four orders of similar strength. Under high magnification, densely spaced regular commarginal threads are visible, particularly well developed at the crest of radial ribs. Details of internal shell morphology unknown. Right valve not observed. Dimensions. PIMUZ 28692, length 13.5 mm, height 14 mm; PIMUZ 28693, length 15 mm, height 16 mm; PIMUZ 28694, length >10 mm, height 11.5 mm. Discussion. Because of the prevailing absence of right valves (see above) and insufficient knowledge of internal shell details, separation of species in Leptochondria chiefly relies on differences in the ornament pattern of the left valve. In addition, differences in the shape of the disc and auricles may be used. Unfortunately, there is considerable variability of these characters in Leptochondria, which makes it often difficult to establish discrete character sets for different species. The unusually slender and densely spaced radial riblets, ventrally intercalated in three or four orders, suggest assignment of the present form to L. curtocardinalis. Contrary to the material described by Newell and Boyd (1995, p. 69), however, the anterior auricle in our specimens is shorter than the posterior one and indistinctly delimited. The left posterior auricle shows a very shallow sinus (Fig. 7A, C). Thus, our assignment to L. curtocardinalis is tentative. Occurrence. USA, Late Permian (Park City Formation), ?Induan (Woodside Formation), Olenekian (Thaynes Formation); ?Pakistan, Spathian (NI) of the Narmia section. This is a rare example of a species that apparently survived the end-Permian mass extinction. Palaeoecology. Epifaunal byssate filter feeder, pleurothetically reclining on the flat right valve. Leptochondria xijinwulanensis Sha, 1995 Figure 7D–J * 1995 Leptochondria? xijinwulanensis Sha, p. 94, pl. 26, figs 1–6. 1995 Leptochondria albertii (Goldfuss); Sha, p. 92, pl. 26, fig. 9. 1995 Leptochondria cf. albertii (Goldfuss); Sha, p. 92, pl. 26, fig. 7. 1996 Leptochondria? xijinwulanensis Sha, 1995; Sha and Grant-Mackie, pl. 3, fig. j. Material. Nine left valves and eight fragments from LAN-B6 (PIMUZ 28698–28704 and unnumbered). Description. Shell size small for the genus. Left valve subcircular in outline, acline to slightly prosocline but rather symmetrical in shape, moderately inflated. Umbo relatively broad, orthogyrate. Dorsal margin straight, equalling about half of shell length. Anterior auricular margin nearly perpendicular to dorsal margin, posterior auricular margin slightly sinuate. Both auricles indistinctly delimited. Growth lines visible on auricles but effacing on disc. Ornament of about 15–30 strong radial ribs of first order, relatively widely spaced, with rounded and symmetrical crest. Second-order ribs weak, irregularly inserted by intercalation on distal part of disc. Internal details unknown, right valve not observed. Dimensions. PIMUZ 28698, length 8 mm, height 8 mm; PIMUZ 28702, length >7.5 mm (incomplete), height 9 mm; PIMUZ 28704, length 6 mm, height c. 6 mm. Discussion. Based on their symmetrical shape, moderate inflation, small and subequal auricles and radial ornament, these left valves can be attributed to Leptochondria. However, the very small size and widely spaced radial ribs are unique for this genus. Based on this feature and the overall similarity, we assign our material to L. xijinwulanensis from the Olenekian of Qinghai, China. Occurrence. USA, Smithian (Thaynes Formation) of Utah (R. Hofmann, pers. comm., 2010); Pakistan, Spathian (Topmost Limestone) of the Landu section; South China, Olenekian (Hantaishan Group). Palaeoecology. Epifaunal byssate filter feeder, pleurothetically reclining on the flat right valve. Leptochondria viezzenensis (Wilckens, 1909) Figure 7K–R * 1909 Pecten viezzenensis Wilckens, p. 147, pl. 5, fig. 25. 1972 Leptochondria viezzenensis (Wilckens, 1909); Allasinaz, p. 259, p. 31, figs 5–9. WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN Material. Two left valves from NAM-B8 (PIMUZ 28706 and 28707); four left valves from NAM-B9 (PIMUZ 28689, 28690, 28705 and 28708); two left valves from LAN-B3 (PIMUZ 28678 and unnumbered); a single left valve from LAN-B4 (PIMUZ 28709). Emended diagnosis. Leptochondria with relatively long dorsal margin and shallow sinus in the posterior auricle of left valve. Shell length slightly exceeding height. Ornament of moderately spaced radial ribs of different strength, increasing in number by intercalation. Description. Shell medium sized to relatively large for the genus. Left valve subcircular in outline, infracrescent, length slightly exceeding height, weakly inflated. Umbo halfway of dorsal margin, not projecting above it. Dorsal margin straight and relatively long (Fig. 7K), equalling two-thirds of shell length in small individuals and slightly less in larger ones. Anterior auricle well differentiated from disc, subtriangular with blunt angle towards dorsal margin. Posterior auricle with shallow sinus (e.g. Fig. 7K), forming rounded edge with dorsal margin. Ornament of auricles indistinctly passing into ornament of disc. Ornament consisting of two or more orders of intercalating, moderately spaced radial ribs (around 40 on disc), weakening in strength towards umbo and with decreasing order. In one supposedly juvenile left valve (Fig. 7R), height slightly exceeds length, with a retrocrescent shape and beak situated at the anterior one-third of the dorsal margin. Details of the internal structures unknown. Right valve not observed. Dimensions. PIMUZ 28705, length 18 mm, height 16 mm; PIMUZ 28708, length 12 mm, height 11 mm; PIMUZ 28678, length >20 mm (incomplete), height 21 mm; PIMUZ 28689, length 12 mm, height 13 mm. Discussion. General characteristics and outline of these left valves are indicative of Leptochondria. However, a larger and weakly sinuated posterior auricle as well as a H ⁄ L ratio of <1 and a relatively long dorsal margin are relatively uncommon features in this genus. So far, this combination of traits has only been described for L. viezzenensis from the upper Ladinian of the Dolomites (Alps). In the original specimen (see Wilckens 1909, pl. 5, fig. 25), the left posterior auricle is broken, but the illustrations by Allasinaz (1972, p. 259, p. 31, figs 5–9) clearly show this feature. Thus, in spite of the extensive stratigraphical gap and palaeogeographical distance between the occurrences, we include these specimens in L. viezzenensis. A sinuate left posterior auricle as seen in L. viezzenensis has not been recorded in congeneric forms. However, line drawings of ‘Pecten ex aff. alberti Goldfuss’ in Bittner (1899, pl. 2, figs 3, 4) show a sinus in the posterior auricles of two left valves that were later attributed to Leptochondria minima (Kiparisova, 1938, p. 246). However, they differ from L. viezzenensis by auricular shape and commarginal ornament. Also the plaster cast of the holotype of L. virgalensis (von Wittenburg, 1909) illustrated 1059 by Nakazawa (1996, pl. 1, fig. M) reveals a sinus very similar to our material. Its ornament, however, clearly differs from that of L. viezzenensis (see below). Leptochondria bittneri (Kiparisova, 1938) is similar to L. viezzenensis in the style of ornament, but differs in lacking a sinuate left posterior auricle and in being substantially taller than long, while L. alberti (Goldfuss 1833– 1840) has more, denser and finer ribs than L. viezzenensis. Occurrence. Pakistan, Spathian (NI) of the Nammal and Landu sections; Italy, Middle Triassic (upper Ladinian) of the Cima Viezzena. Palaeoecology. Epifaunal byssate filter feeder, pleurothetically reclining on the flat right valve. Leptochondria virgalensis (von Wittenburg, 1909) Figure 7S–W * 1909 Pecten (Leptochondria) albertii Goldf. n. var. virgalensis von Wittenburg, p. 8, pl. 3, fig. 4. 1996 Leptochondria virgalensis (Wittenburg, 1909); Nakazawa, p. 217, pl. 1, figs K, M. 1996 Leptochondria virgalensis Wittenburg; Sha and Grant-Mackie, p. 438, pl. 3, fig. N. Material. Six left valves and three fragments from LAN-B1 (PIMUZ 28710, 28711, 28712, 28713 and unnumbered); two left valves and one fragment from NAM-B3 (PIMUZ 28714 and unnumbered). Description. Left valve subcircular in outline, infracrescent to slightly retrocrescent, weakly to moderately inflated. Beak halfway of short and straight dorsal margin, only slightly projecting above it or not at all. Maximum inflation slightly behind mid-line of disc. Anterior auricle right angled to obtuse, posterior auricle obtuse, both indistinctly delimited from disc. Ornament of very fine, closeset radial ribs (>70), intercalating in three or four ranks. Few ribs of first order more prominent than average (7–15 prominent ribs per valve, separated by 3–10 weaker ribs each). Commarginal growth lines very fine, densely spaced. Internal structures and hinge structures unknown. Right valve not observed. Dimensions. PIMUZ 28710, length 8 mm, height 9 mm; PIMUZ 28711, length >9 mm, height 10 mm; PIMUZ 28712, length >5.5 mm (about 50 per cent missing), height 11 mm; PIMUZ 28713, length 6 mm, height 6.5 mm; PIMUZ 28714, length 13.5 mm, height 14 mm. Discussion. Leptochondria virgalensis differs from L. curtocardinalis in bearing 7–15 more prominent radial ribs, in having a smaller size and in being more inflated. Own material of L. virgalensis from the Ceratite Marls of Nammal shows that the extraordinarily prominent ribs are stronger in these stratigraphically older specimens. 1060 PALAEONTOLOGY, VOLUME 55 A morphocline of decreasing strength of these ribs leading from L. virgalensis to L. curtocardinalis appears possible from the stratigraphical distribution. Occurrence. Pakistan, Dienerian (Salt and Surghar Ranges; see von Wittenburg 1909) and late Smithian of the Nammal (BB) and Landu (UCL) sections; South China, Olenekian (Hantaishan Group). Palaeoecology. Epifaunal byssate filter feeder, pleurothetically reclining on the flat right valve. Suborder ENTOLIIDINA Hautmann in Carter et al., 2011 Superfamily ENTOLIOIDEA von Teppner, 1922 Discussion. In spite of its relatively low taxonomic diversity and morphological disparity, this group has recently been raised to the rank of a suborder to avoid polyphyly of Pectinidina (Hautmann 2010; Carter and Hautmann 2011). Family ENTOLIIDAE von Teppner, 1922 Genus SCYTHENTOLIUM Allasinaz, 1972 Type species. Pecten tirolicus von Wittenburg, 1908, by original designation. Scythentolium kokeni (von Wittenburg, 1909) Figure 8A–L *. 1909 Pecten kokeni Wittenburg, p. 7, pl. 2, figs 3, 4. . 1972 Scythentolium kokeni (Wittenburg); Allasinaz, p. 310, pl. 41, figs 6, 7. p. 1996 Scythentolium kokeni (Wittenburg), 1909; Nakazawa, p. 222, pl. 2, figs E–H, ?I. Material. Three left valves and 16 fragments from NAM-B1; three fragments from NAM-B2; one fragment from NAM-B3; one fragment from NAM-B4; one fragment from NAM-B7; three left valves and one fragment from NAM-B9; three left valves and one fragment from NAR-B1; two fragments (one juvenile valve) from LAN-B2; one fragment from LAN-B3; six left valves and three fragments form LAN-B4; one fragment from LAN-B6. Description. Shell thin, discs circular in outline. Beaks of both valves pointed, orthogyrate to slightly prosogyrate, slightly protruding above dorsal margin. Dorsal margin straight and short, comprising 40 per cent or less of shell length. Disc of left valve with convex centre and flattened anterior and posterior borders. Left anterior auricle with shallow sinus (Fig. 8F). Left posterior auricle obtusely subtriangular (Fig. 8A). Ornament of left valve with well-developed and regularly spaced growth lines and about 25 weak but distinct, broadly spaced radial ribs on the disc of the left valve (Fig. 8H). Right valve similar to left but probably primary without radial ribs. Internal shell structures not observed. Dimensions. PIMUZ 28724, length c. 27 mm, height c. 25 mm; PIMUZ 28725, length 25 mm, height 26 mm; PIMUZ 28726, length 31 mm, height 29 mm; PIMUZ 28695, length 26 mm, height c. 28 mm; PIMUZ 28696, length >24 mm, height >26 mm (incomplete); PIMUZ 28727, length 34 mm, height c. 30 mm. Discussion. According to von Wittenburg (1909), Allasinaz (1972) and Nakazawa (1996), Scythentolium kokeni has a straight dorsal margin, slightly sinuated anterior auricles and weak radial ribs on the left valve. Our material shows all these characters and covers essentially the same stratigraphical interval as that of previous authors. As stated by Nakazawa (1996, p. 223), the anterior auricular sinus of S. kokeni is relatively weak for the genus. F I G . 8 . A–L, Scythentolium kokeni (von Wittenburg, 1909). A, PIMUZ 28717, left valve from LAN-B4, ·2. Note commarginal ornament and slightly sinuated anterior auriclar margin. B, PIMUZ 28718, left valve from LAN-B4, ·1. Note commarginal and very faint radial ornament. C, PIMUZ 28719, fragment of left valve from LAN-B4, ·1. D, PIMUZ 28722, fragment of left valve from LAN-B4, ·1. E, PIMUZ 28723, left valve from LAN-B4, ·2. F, PIMUZ 28675, fragment of left valve from NAM-B9, ·2. Note curved growth lines on anterior auricle. G, PIMUZ 28724, left valve from NAM-B9, ·1. Note radial ribs; anterior auricle damaged. H, PIMUZ 28725, left valve from NAM-B9, ·1. Note radial ribs. I, PIMUZ 28726, left valve from NAM-B9, ·1. Note radial folds on anterodorsal disc and radial ribs on ventral half. J, PIMUZ 28727, right valve from NAM-B1, ·2. Anterior auricle incomplete. K, PIMUZ 28728, left valve from NAM-B1, ·1. Note weak radial ornament. L, slab with three left valves from NAR-B1, ·1. PIMUZ 28695, valve on the right. Anterior auricle incomplete but incremental lines indicate shallow anterior sinus. PIMUZ 28696, valve on the left. Note faint radial ribs. PIMUZ 28697, juvenile specimen in upper left corner. Note faint radial ribs. M, Plagiostoma? sp., PIMUZ 28681, fragment from LAN-B6, ·2. Note ornament. N–T, Permophorus costatus (Brown, 1841). N, O, PIMUZ 28732, right valve from LAN-B5. N, lateral view, ·2. Note reticulate ornament. O, dorsal view, ·2. Note slightly arched posterior dorsal margin and long, narrow escutcheon. P, PIMUZ 28729, right valve from LAN-B5, ·2. Q, PIMUZ 28734, left valve from NAR-B1, ·2. R, PIMUZ 28733, left valve from LAN-B5, ·2. Specimen partially covered by sediment. S, PIMUZ 28730, interior of left valve from LAN-B5, ·2. Note thick shell, division of posterior adductor scar (arrow, pa) and pallial line (pl). T, PIMUZ 28731, juvenile right valve from LAN-B5, ·2. Note reticulate ornament. U, Astartella? sp. nov., PIMUZ 28735, internal mould of poorly preserved ?left valve from NAM-B7, ·2. V–X, Pseudocorbula? sp. nov., both specimens from NAM-B8. V, PIMUZ 28736, left valve, ·2. W, X, PIMUZ 28737, left valve, ·2. W, lateral view. Note growth lines. X, dorsal view. Note strongly prosogyrate umbo, lack of escutcheon and strongly truncate posterior margin. WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN 1061 C E B D A F H G I K L J M Q N P U O T W R S V X 1062 PALAEONTOLOGY, VOLUME 55 Ornament in Scythentolium kokeni differs widely with state of preservation; for instance, left valves from LANB4 preserve the radial ornament only faintly (Fig. 8B, C) or not at all (Fig. 8A, D), possibly due to recrystallization. In specimens from NAR-B1, radial ribs as well as commarginal growth threads are very faint (Fig. 8L). Judging from the literature, however, it appears that the right valve primarily lacks radial ribs (Allasinaz 1972). On one juvenile valve, radial ribs are slightly stronger and fewer in number (Fig. 8L). Occurrence. Pakistan, Smithian and Spathian of several sections in the Salt and Surghar Ranges (von Wittenburg 1909; Nakazawa 1996; the present study). Palaeoecology. Epifaunal sessile filter feeder. The paedomorphic reactivation of the byssal notch in this genus indicates at least a facultative sessile mode of life (Hautmann et al. 2011). Order LIMOIDA Waller, 1978 Superfamily LIMOIDEA Rafinesque, 1815 Family LIMIDAE Rafinesque, 1815? Genus DIMORPHOCONCHA gen. nov. Type species. Dimorphoconcha globosa sp. nov. Derivation of name. Referring to the pronounced morphological difference between the proximal and distal part of the shell. Diagnosis. Left valve suboval in outline, slightly procrescent. Proximal part of disc well inflated, covered with faint oblique ribs, contrasted by flat, fringe-like and strongly plicate ventral margin oriented parallel to the commissural plane. Small gaps present between (inferred) anterior shell margins. Discussion. To our knowledge, no comparable genus has ever been described. Taxonomic assignment is hampered by the absence of opposite (inferred right) valves and the nonpreservation of the hinge. Limids are procrescent and have a slightly winged dorsal margin, gaping anterior margins and mostly bear radial ribs (Cox and Hertlein in Cox et al. 1969). Assignment of Dimorphoconcha gen. nov. to the Limidae is compatible with these characters, particularly with the presence of small gaps between the (inferred) anterior shell margins. Although the dorsal margin is not preserved, the outline of the valves suggests the presence of a relatively broad dorsal margin indicative of the presence of auricles, as in limids. We are not aware of any other bivalve family that would match the observed character pattern of our specimens. Thus, we tentatively assign this new genus to the Limidae. However, the abrupt change in shape and ornament of Dimorphoconcha globosa gen. nov., sp. nov. is unique within that family. Such a feature has been observed in the Late Triassic Persia Repin, 1996, a genus assigned to the Prospondylidae Ptschelinceva, 1960 (emend. Hautmann 2001b), which was cemented to the substrate by its right valve. Left valves of Persia abruptly change their ornament from thread-like radial ribs, corresponding to the cemented area of the adjacent valve, to coarsely plicate ribs distally, corresponding to the free-growing area of the opposite valve, which is also plicate (Hautmann 2001a, b). Some species assigned to the ?prospondylid Enantiostreon Bittner, 1901 also resemble our specimens in having an irregular suboval shape and a plicate margin (see discussion below). However, because prospondylids are retrocrescent, our specimens would represent right valves if assigned to that family (contrary to our placement within limids) and consequently an attachment scar would be expected, which is not observed. Thus, Dimorphoconcha gen. nov. was not cemented, unless assigned to the Ostreoidea Rafinesque, 1815, which are attached to the substrate by their left valves (Stenzel 1971). However, oysters have a less regular shape and lack auricles (Hautmann 2001b). Also the scar of attachment of their left valve is commonly replicated in the opposite valve as a xenomorphic area near the contact of both valves. Finally, the presence of small gaps between valves suggests the presence of a byssus extrusion in the adult animal, which contradicts a cemented mode of life. Dimorphoconcha globosa sp. nov. Figure 9 Derivation of name. From the Latin word globosus for orbicular, referring to the globose centre of the shell. Holotype. PIMUZ 28669, a ?left valve from NAM-B7 (Fig. 9A, B). Diagnosis. As for the genus. Material. In addition to the holotype, one ?left valve (PIMUZ 28670; Fig. 9C) with preserved external shell layer, and one very small fragment from NAM-B6. Description. ?Left valve suborbicular to subovate, slightly procrescent. Proximal portion of disc well inflated, regular (Fig. 9A, B) to slightly irregular (Fig. 9C) in shape. Abrupt change from inflated proximal part of disc to flat marginal fringe. Marginal fringe broad, strongly plicate, parallel to the commissural plane. Plicae lower towards anteroventral margin. Anterodorsal margin slightly gaping towards commissural plane. Plicae absent on posterodorsal margin, which shows commarginal threads (Fig. 9C). Commarginal WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN 1063 A C B D Dimorphoconcha globosa gen. nov., sp. nov. A, holotype (PIMUZ 28669), left valve from NAM-B7, outer portion of external shell layer split off (see B), ·2. lp: area with low plicae on anterior ventral margin; bg: supposed byssal gape. B, external half of same individual, with partially adhering shell material, view of inner side, ·2. Note oblique ribs. C, PIMUZ 28670, left valve from NAM-B6, internal view, ·2. Note remnant of the recrystallized middle shell layer in dorsal part of shell. lp: area with low plicae on anterior ventral margin. D, Shell microstructure of the outer shell layer of Dimorphoconcha globosa gen. nov., sp. nov., acetate peel of PIMUZ 28669 from NAM-B7. Despite recrystallization, relict structures suggestive of a simple prismatic microstructure are visible. Scale bar represents 1 mm. FIG. 9. growth lines fine (Fig. 9A, B) or thickened to slightly irregular threads (Fig. 9C), superimposed by oblique riblets symmetrical in shape (Fig. 9A, B). Shell moderately thick, external shell layer simple prismatic (Fig. 9D), probably primary calcitic, inner shell layer recrystallized, thus by inference originally aragonitic. Internal details not observed. ?Right valve not known. Dimensions. PIMUZ 28669, length c. 25 mm, height c. 25 mm; PIMUZ 28670, length 26 mm, height c. 29 mm. Discussion. Left ⁄ right interpretation of the valves in the description and diagnosis above relies on our preferred assignment to the Limidae. The gap at the anterior shell margin is interpreted as a byssal gap. The oblique riblets (Fig. 9A) probably represent a replica of the ornament of the shell exterior. In fragmentary material, the plicate fringe of Dimorphoconcha gen. nov. may lead to confusion with Entantiostreon (see above). An example is Enantiostreon cf. difforme (von Schlotheim, 1820) from the upper Gri- esbachian of East Greenland figured Spath (1935, pl. 20, fig. 8), which could be assigned to either genus. Occurrence. Pakistan, Spathian (BB) of the Nammal section. Palaeoecology. Epifaunal byssate filter feeder, inferred from the presence of a byssal gape and the life habit of recent limids (Cox in Cox et al. 1969, p. N9). Some limids also possess the ability to swim after having detached from the substrate (Cox in Cox et al. 1969, p. N9). Genus PLAGIOSTOMA J. Sowerby, 1814 Plagiostoma? sp. Figure 8M Material. Three incomplete valves from LAN-B6 (PIMUZ 28681 and unnumbered). 1064 PALAEONTOLOGY, VOLUME 55 Description. Valves procrescent and moderately inflated. Ornament of densely spaced radial ribs with relatively broad, gently rounded and symmetrical crests. Dimensions. Only incomplete valves available, which, however, indicate a relatively small size for the genus (height c. 20 mm). Discussion. Shape and style of ornament are suggestive of Plagiostoma. The sole record of this genus from the Lower Triassic known to us is that of P. aurita (Popow, 1964 from the Olenekian of north-east Russia (Dagys and Kanygin 1996), which differs in particular in being smooth externally. Pseudolimea kaplani (Kurushin, 1987) from the same area differs in having much coarser radial ribs. Occurrence. Pakistan, Spathian (Topmost Limestone) of the Landu section. Palaeoecology. Epibyssate filter feeder, resting orthothetically on umbones and flattened anterior shell margin on the substrate (Seilacher 1954). Subclass HETEROCONCHIA Hertwig, 1895 Superorder PALAEOHETERODONTA Newell, 1965 Order MODIOMORPHOIDA Newell, 1969 in Cox et al., 1969 Superfamily MODIOMORPHOIDEA Miller, 1877 Family KALENTERIDAE Marwick, 1953 Genus PERMOPHORUS Chavan, 1954 Type species. Arca costata Brown, 1841, by monotypy. Permophorus costatus (Brown, 1841) Figure 8N–T * 1841 Arca costata Brown, p. 66, pl. 6, figs 34, 35. 1881 Pleurophorus acuteplicatus Waagen, p. 223, pl. 18, fig. 10a–e (juvenile valve). ? 1931 Pleurophorus costatus Brown; Frebold, p. 14, pl. 1, fig. 19. 1933 Pleurophorus costatus Brown; Frebold, p. 24, pl. 3, fig. 16. 1967 Permophorus costatus (Brown); Logan, p. 53, pl. 9, figs 1–13 (synonymy). Material. One left valve from NAR-B1 (PIMUZ 28734); three right and three left valves from LAN-B5 (PIMUZ 28729–28733 and unnumbered). Description. Valves subtrapezoidal, posteriorly elongated, length about one-third to one-quarter of height. Juvenile valve relatively less elongated than fully grown specimens (Fig. 8T). Shell weakly to moderately inflated, about equiconvex. Beaks within anterior one-fifth of shell length. Dorsal margin long and straight (Fig. 8N). Posterior dorsal margin slightly arched, forming long and narrow escutcheon (Fig. 8O). Ornament with 5–6 strong radial ribs on posterior segment of valve, and weak commarginal threads covering entire surface. Reticulate pattern in posterior and posteroventral region by combination of radial ribs and commarginal threads. Impression of posterior adductor scar shallow and relatively large, located near distal end of posterior dorsal margin (Fig. 8S). Faint line dividing muscle scar into two compartments of similar size (Fig. 8S). Pallial line integripalliate (Fig. 8S). Shell thick, completely recrystallized, thus by inference originally aragonitic. Details of the hinge not observed. Dimensions. PIMUZ 28729, length 19 mm, height 7 mm; PIMUZ 28734, length 22 mm, height 9 mm; PIMUZ 28732, length 12 mm, height 5 mm; PIMUZ 28731, length 6 mm, height 3 mm. Discussion. The shallow line running across the posterior adductor is of unknown origin and has not yet been described for this genus. It could represent a growth line of the myostracum formed during growth displacement of the muscle, or a separation of a distally positioned catch muscle and an anterior quick muscle. Although the hinge details of this species, as described by Logan (1967, p. 53), cannot be verified in our material, the identity in shape and style of ornament leaves no doubts over its assignment to Permophorus costatus. To date, two additional species have been described from the Lower Triassic. Ciriacks (1963, p. 83, pl. 16, figs 8, 9) recorded Permophorus? bregeri Girty, 1927 from the Induan (Dinwoody Formation) of Idaho, USA. This species differs from our material in its less elongated shape and more acutely angular (almost rectangular) dorsal margin, as well as in the absence of 5–6 distinct radial ribs. Permoporus triassicus Newell and Boyd, 1999 (pp. 2, 3, textfig. 2) from the Spathian (Thyanes Formation) of the central Rocky Mountains, USA, also clearly differs from P. costatus in its oval outline and lack of ornament. A juvenile left valve of Permophorus from the Upper Permian of the Salt Range (Upper Productus Limestone of Virgal) was described as P. acuteplicatus by Waagen (1881, p. 223, pl. 18, fig. 10a–e). We believe that this species is synonymous with P. costatus based on the ornament recorded and on its proportions that are comparable with the juvenile specimen in our material and with those illustrated by Logan (1967, pl. 9, figs 2, 3). This is the first record of P. costatus form the Triassic. The stratigraphically oldest record of this species is from the base of the Zechstein in Germany (Fulda 1935), dated at c. 258 Ma (Menning et al. 2005). With the new Early Triassic age assignments by Galfetti et al. (2007c), a minimum longevity of c. 8 Myr can be inferred for P. costatus, with a duration of its Early Triassic outage (ranging from WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN the Griesbachian–Smithian, plus the base of the Spathian) in excess of 2.1 Myr. Thus, Permophorus costatus is not only remarkable for its unusual longevity, but also for its long absence from the fossil record (i.e. the Lazarus phenomenon of Jablonski 1986). Occurrence. East Greenland, Late Permian (Cape Stosch Formation); northern Europe, Late Permian (Zechstein, Germany; Magnesian Limestone, England); Pakistan, Late Permian (Salt Range, top of Upper Productus Limestone of Virgal; Waagen 1881) and Spathian (NI) of the Narmia and Landu sections. Palaeoecology. Semi-infaunal or infaunal filter feeder. Stanley (1972, p. 195) proposed an endobyssate mode of life, inferred from the anterior reduction in P. costatus. However, the species might have possessed a reduced foot used for sluggish re-burrowing if exhumed (Stanley 1972, p. 195). 1065 Triassic Astartella sp. of Hautmann et al. (2011, pp. 79– 80) or the Permian A. tunstallensis King, 1850 and A. vallisneriana King, 1848. Alternatively, it could be assigned to Astratopis von Wöhrmann, 1889, but this appears less convincing because of the commonly truncated posterior margin in that genus. Occurrence. Pakistan, Spathian (BB) of the Nammal section. Palaeoecology. Infaunal burrowing filter feeder, in analogy to recent astartids. Superfamily CRASSATELLOIDEA de Férussac, 1822 Family MYOPHORICARDIIDAE Chavan in Vokes, 1967 Genus PSEUDOCORBULA Philippi, 1898 Pseudocorbula? sp. nov. Order CARDITOIDA Dall, 1889 Superfamily CRASSATELLOIDEA de Férussac, 1822 Family ASTARTIDAE d’Orbigny, 1844 Genus ASTARTELLA Hall, 1858 Type species. Astartella vera Hall, 1858. Astartella? sp. nov. Figure 8U Material. A single external mould of a ?left valve (PIMUZ 28735) from NAM-B7. Description. Single ?left valve, trigonally rounded to slightly pyriform in outline, weakly inflated, height exceeding length, with umbo at about half of shell length. Anterior ventral margin rounded, posterior margin slightly truncated. Concentric ornament of faint regularly spaced ribs, visible only on dorsal half of valve. No internal details known. Dimensions. Length 6 mm, height 7 mm. Discussion. Astartids have trigonally suboval valves that are usually commarginally ribbed, at least in early growth (Chavan in Cox et al. 1969, p. N562). Our poorly preserved external mould shows traces of a concentric ornament typical of the family and resembles Astartella in shape. It is thus tentatively attributed to that long-lived genus, which first appeared in the Late Carboniferous (Chavan in Cox et al. 1969, p. N563) and ranged up into the Lower Triassic (Hautmann et al. 2011). However, the slightly pyriform outline of PIMUZ 28735 is a peculiar feature that sets it apart from congeners, such as the Early Figure 8V–X Material. Two left valves (PIMUZ 28736 and 28737) from NAM-B8. Description. Left valve subtriangular to subquadrangular, moderately inflated. Anterior margin curved, posterior margin truncated. Beaks strongly prosogyrate, at anterior one-third of shell length, abutting commissural plane. Lunule small. Surface smooth, covered with growth lines only. Shell thin. Details of shell interior unknown. Dimensions. PIMUZ 28736, length 14 mm, height 14 mm; PIMUZ 28737, length 14 mm, height 13 mm. Discussion. The external morphology of myophoricardiids is characterized by inequilateral valves with subtriangular to trapezoidal shape and truncated posterior margins, prosogyrate umbones situated anteriorly to mid-length and the presence of a distinct posterior ridge or carina (e.g. Cox and Chavan in Cox et al. 1969, pp. N580–582). Our specimens share these characters and most closely resemble Pseudocorbula in having a blunt posterior ridge rather than a sharp carina. However, assignment to that genus is tentative because details of the hinge are unknown. Alternatively, assignment to a new genus of either Astartidae or Cardiniidae von Zittel, 1881 does not appear impossible, but is less likely because the present specimens lack the commarginal ribs of the former and the thick shell of the latter. Occurrence. Pakistan, Spathian (NI) of the Nammal section. Palaeoecology. Infaunal mobile filter feeder. Short and posteriorly truncated valves are characteristic of shallow-infaunal burrowing species (Hautmann 2001b, p. 130). 1066 PALAEONTOLOGY, VOLUME 55 EVOLUTIONARY CONTEXT Diversity An overview of samples, species occurrences and number of individuals is given in Figure 2. In the systematic section above, 15 species in 11 genera and 10 families are described from the upper Smithian to middle Spathian of the Salt Range and Surghar Range. When considered separately, 14 species belonging to 11 genera are reported from the Spathian. This is not unusual for this time interval and comparable to the Olenekian (Werfen Formation) with 12 genera recorded (Posenato 2008). In the Induan of the Salt and Surghar Ranges, six bivalve species in five genera have been noted (von Wittenburg 1909; Nakazawa 1996, fig. 3). Similarly, five genera have been recognized in the Induan of the Werfen Formation (Posenato 2008), whereas much more diverse faunas with more than 10 genera have been recorded from the Griesbachian (lower Induan) of other localities (Far East Russia, Primorye: Kumagae and Nakazawa 2009; South China: Hautmann et al. 2011). However, these exceptionally diverse faunas might represent early aborted (i.e. shortlived) recovery events or stem from different, more productive environments. Thus, until further data are available, a substantial diversity increase from the Induan to the Olenekian of the Salt Range and Surghar Range is conjecturable. As major environmental perturbations have been proposed for the Smithian ⁄ Spathian boundary (Brayard et al. 2006; Galfetti et al. 2007b), a comparison of diversity between the Smithian and Spathian samples recorded herein would be of great interest, as it might enable to shed some light on the reaction of bivalves to this event. Unfortunately, comparisons between Smithian and Spathian diversities are not tenable because of the limited number of species, differences in sample sizes and the low number of samples from the Smithian. Palaeobiogeography Six of the genera recorded herein have Panthalassan records in the Early Triassic (Japan, USA; Palaeoneilo, Pinna, Bakevellia, Leptochondria, Scythentolium and Permophorus), four have Tethyan records (Bakevellia, Leptochondria, Scythentolium and Astartella), one has been described from the boreal (Plagiostoma) and three are known exclusively from Pakistan, at least during the Olenekian (Eobuchia, Dimorphoconcha and Pseudocorbula). On the species level, a much higher proportion of taxa appears confined to the study area (10 of 15; Table 1). The distribution pattern of the few species known also from the Lower Triassic elsewhere is similar to that of the genera. Three species have Panthalassan records from Japan (Pinna muikadanensis) and the western USA (Leptochondria cf. curtocardinalis and L. xijinwulanensis). The latter also occurs in western China. An Early Triassic Tethyan species is Leptochondria virgalensis, which has also been described from South China (Sha 1995; Sha and Grant-Mackie 1996). Leptochondria viezzenensis is another Tethyan form that, however, has been reported from the palaeogeographically and stratigraphically distant Ladinian of northern Italy. The disparate biogeographical distribution described above is surprising and may indicate an unexpectedly high faunal exchange between the southern Tethys and Panthalassa. On the species level, the high number of possibly endemic taxa seems to contradict the claim that during the entire Early Triassic, bivalve faunas were relatively homogeneous worldwide (Schubert and Bottjer 1995; Hallam and Wignall 1997). Our data may indicate increasing provincialism towards the end of the Early Triassic, possibly reflecting the progress in recovery of marine benthos. A trend of increasing regional differentiation during the Early Triassic has also been observed in ammonoids, with the exception of a reset related to the end-Smithian extinction event (Brayard et al. 2006, 2009; Galfetti et al. 2007a). Alternatively, the high number of bivalve taxa restricted to the Pakistani localities during the Smithian and Spathian and the disparate palaeogeographical similarities might in part reflect insufficient knowledge of benthic faunas of that age in most other areas. Palaeoecology The genera are assigned to five basic life habits (infaunal detritus feeder; infaunal filter feeder, semi-infaunal filter feeder; epifaunal filter feeder; swimming filter feeder), which also roughly represent ecological niches (Table 1). Assignments have been made on the basis of constructional morphology, as discussed in the systematic section where appropriate, or inferred from extant representatives of the respective families (Cox et al. 1969). From the presence of four life habits within Spathian samples (the swimming life habit is questionably represented by Scythentolium kokeni, which could be interpreted as a facultative swimmer) and up to three within one sample, ecologically moderately diverse communities can be inferred. However, no ecological trends are recognized in Spathian samples, as the ecological categories do not cluster. Additionally, comparisons within the sample, especially between Spathian and Smithian are not significant for reasons outlined above. Three samples show a marked predominance of few taxa: NAM-B9, where the epifaunal byssate genus Eobuchia is largely dominant (D = 0.54), and NAM-B8 and NAM-B7 in which the detritus feeder Palaeoneilo predominates (NAM-B8: D = 0.84; NAM-B7: D = 0.56). WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN Pseudocorbula? sp. nov. · · · · · Permophorus costatus Plagiostoma sp. Dimorphoconcha globosa sp. nov. Scythentolium kokeni Leptochondria virgalensis Leptochondria viezzenensis Leptochondria xijinwulanensis Leptochondria cf. curtocardinalis Eobuchia? sp. nov. Eobuchia punjabensis Bakevellia? sp. nov. Astartella? sp. nov. Palaeobiogeography Late Permian USA Europe and Greenland Early Triassic Southern Japan USA South China Restricted to Pakistan Middle Triassic Italy Evolutionary fate Palaeozoic survivor genus Genus newly evolved, extending beyond Early Triassic Genus newly evolved, restricted to Early Triassic Ecology Infaunal det. f. Infaunal f. f. Semi-infaunal f. f. Epifaunal f. f. Taxonomy Newly described species Newly described genus Pinna muikadanensis Summary of palaeobiogeographical and ecological data and evolutionary context. Paleoneilo? fortistriata TABLE 1. 1067 · · · · · · · · · · · · · · ? · ? · · · · · · · · · · · · · · · · · · · · · · · · · · This may reflect some environmental stress or simply substrate conditions, water energy and presence of organic particles in the sediment. The samples containing only one species are not discussed here because they are either very small, poorly preserved or contain additional species that could not be separated from the host rock, and thus, their identity remained obscure (e.g. NAM-B1). Evolution Evolutionary implications of single taxa are discussed in the systematic section of this work. However, it is worthy · · · · · · · · · · of note here the two Permian species, Leptochondria curtocardinalis and Permophorus costatus, which we recognized also within our Early Triassic material, albeit tentatively in the case of the former. For P. costatus, a longevity of >8 Myr and an absence from the fossil record of >2.1 Myr have been inferred (see above). According to Hallam and Wignall (1997, p. 14), Lazarus taxa have previously only been identified above the species rank (genera or higher). Our new finds may thus represent the first examples of true Lazarus species. Table 1 presents an overview of the evolutionary context of each taxon. Six long-term survivor genera ranging back to the Permian are reported in the present study 1068 PALAEONTOLOGY, VOLUME 55 (Palaeoneilo, Pinna, Bakevellia, Leptochondria, Permophorus and Astartella). Thus, despite a few newly evolved genera bound to disappear soon (Eobuchia, Scythentolium and Dimorphoconcha), the fauna is still dominated by Palaeozoic survivor genera. However, on species level diversity is sustained almost exclusively (exceptions discussed above) by forms that remained confined to the Lower Triassic. Acknowledgements. This work was supported by the Swiss National Science Foundation project 200021-121774 (Hautmann and Bucher). We thank R. Posenato and J. W. M. Jagt for helpful comments on an earlier typescript. Editor. John W. M. Jagt. REFERENCES A D A M S , H. and A D A M S , A. 1858. The genera of recent Mollusca arranged according to their organization, 2. Bivalvia. John van Voorst, London, 661 pp. A L L A S I N A Z , A. 1972. Revisione dei Pettinidi Triassici. Rivista Italiana di Paleontologia e Stratigrafia, 78, 189–428. B E G G , J. G. and C A M P B E L L , H. J. 1985. Etalia, a new Middle Triassic (Anisian) bivalve from New Zealand, and its relationship with other pteriomorphs. New Zealand Journal of Geology and Geophysics, 28, 725–741. B E U R L E N , K. 1944. Beiträge zur Stammesgeschichte der Muscheln. Sitzungsberichte der mathematisch-naturwissenschaftlichen Abteilung der Bayerischen Akademie der Wissenschaften zu München, 1, 133–145. B E U S H A U S E N , H. E. L. 1895. Die Lamellibranchiaten des Rheinischen Devon mit Anschluss der Aviculiden. Abhandlungen der königlich-preussischen Geologischen Landesanstalt, neue Serie, 17, 1–514, pls 1–38. B E Y R I C H , H. E. 1862. Zwei aus dem deutschen Muschelkalk noch nicht bekannte Avicula-artige Muscheln. Zeitschrift der deutschen geologischen Gesellschaft, 14, 9–10. B I T T N E R , A. 1891. Triaspetrefakten von Balia in Kleinasien. Jahrbuch der kaiserlich-königlichen Geologischen Reichsanstalt, 41, 97–116. —— 1895. Lamellibranchiaten der alpinen Trias. I. Theil: revision der Lamellibranchiaten von Sct. Cassian. Abhandlungen der kaiserlich-königlichen Geologischen Reichsanstalt, 18, 1–235, pls 1–24. —— 1899. Trias-brachiopoda and lamellibranchiata. Palaeontologia Indica, 15, 1–76, pls 1–12. —— 1901. Lamellibranchiaten aus der Trias des Bakonyer Waldes, Abhandlung 3. 1–107, pls 1–9. In H Ö L Z E L , E. (ed.). Resultate der wissenschaftlichen Erforschung des Balatonsees, Band 1, Teil 1, Anhang: Palaeontologie der Umgebung des Balatonsees, Band 2. Balaton-Ausschuss der Ungarischen Geographischen Gesellschaft, Wien, 107 pp. B O Y D , D. W. and N E W E L L , N. D. 2002. A unique pterioid bivalve from the Early Triassic of Utah. American Museum Novitates, 3375, 1–9. B R A N S O N , C. C. 1930. Paleontology and stratigraphy of the phosphoria formation. Missouri University Studies, 5 (2), 1–99. B R A Y A R D , A. and B U C H E R , H. 2008. Smithian (Early Triassic) ammonoid faunas from northwestern Guangxi (South China): taxonomy and biochronology. Fossils and Strata, 55, 1–179. —— —— E S C A R G U E L , G., F L U T E A U , F., B O U R Q U I N , S. and G A L F E T T I , T. 2006. The Early Triassic ammonoid recovery: paleoclimatic significance of diversity gradients. Palaeogeography, Palaeoclimatology, Palaeoecology, 239, 374– 395. —— —— B R Ü H W I L E R , T., G A L F E T T I , T., G O U D E M A N D , D., G U O D U N , K., E S C A R G U E L , G. and J E N K S , J. 2007. Proharpoceras Chao: a new ammonoid lineage surviving the end-Permian mass extinction. Lethaia, 40, 175–181. —— E S C A R G U E L , G., B U C H E R , H. and B R Ü H W I L E R , T. 2009. Smithian and Spathian (Early Triassic) ammonoid assemblages from terranes: paleoceanographic and paleogeographic implications. Journal of Asian Earth Sciences, 36, 420–433. B R O W N , T. 1841. Description of some new species of fossil shells, found chiefly in the Vale of Todmorden, Yorkshire. Transactions of the Manchester Geological Society, 1, 212–229. B R Ü H W I L E R , T., B R A Y A R D , A., B U C H E R , H. and G O U D U N , K. 2008. Griesbachian and Dienerian (Early Triassic) ammonoid faunas from northwestern Guangxi and southern Guizhou (south China). Palaeontology, 51, 1151– 1180. —— B U C H E R , H., W A R E , D., H E R M A N N , E., H O C H U L I , P. A., R O O H I , G., R E H M A N , K. and Y A S E E N , A. in press. Smithian (Early Triassic) ammonoids from the Salt Range, Pakistan. Special Papers in Palaeontology. C A R T E R , J. G. 1990. Evolutionary significance of shell microstructure in the Palaeotaxodonta, Pteriomorphia and Isofilibranchia (Bivalvia: Mollusca). 135–296. In C A R T E R , J. G. (ed.). Skeletal biomineralisation: patterns, processes and evolutionary trends. Van Nostrand Reinhold, New York, 832 pp. —— A L T A B A , C. R., A N D E R S O N , L. C., A R A U J O , R., B I A K O V , A. S., B O G A N , A. E., C A M P B E L L , D. C., C A M P B E L L , M., C H E N , J I N- H U A, C O P E , J. C. W., D E L V E N E , G., D I J K S T R A , H. H., F A N G , ZO NG- J IE , G A R D N E R , R. N., G A V R I L O V A , V. A., G O N C H A R O V A , I. A., H A R R I E S , P. J., H A R T M A N , J. H., H A U T M A N N , M., H O E H , W. R., H Y L L E B E R G , J., J I A N G , BAO-YU, J O H N S T O N , P., K I R K E N D A L E , L., K L E E M A N N , K., K O P P K A , J., K Ř Í Ž , J., M A C H A D O , D., M A L C H U S , N., M Á R Q U E Z - A L I A G A , A., M A S S E , J.-P., M C R O B E R T S , C. A., M I D D E L F A R T , P. U., M I T C H E L L , S., N E V E S S K A J A , L. A., Ö Z E R , S., P O J E T A , J. J. R., P O L U B O T K O , I. V., P O N S , J. M., P O P O V , S., S Á N C H E Z , T., S A R T O R I , A. F., S C O T T , R. W., S E Y , I. I., S I G N O R E L L I , J. H., S I L A N T I E V , V. V., S K E L T O N , P. W., S T E U B E R , T., W A T E R H O U S E , J. B., W I N G A R D , G. L. and Y A N C E Y , T. 2011. A synoptical classification of the Bivalvia (Mollusca). Paleontological Contributions, 4, 1–47. —— B A R R E R A , E. and T E V E S Z , M. J. S. 1998. Thermal potentation and mineralogical evolution in the Bivalvia (Mollusca). Journal of Paleontology, 72, 991–1010. WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN —— and H A U T M A N N , M. 2011. Shell microstructure of the basal pectinid Pleuronectites laevigatus: implications for pectinoid phylogeny (Mollusca: Bivalvia: Pteriomorphia). Journal of Paleontology, 85, 464–467. C H A V A N , A. 1954. Les Pleurophorus et genres voisins. Cahier Géologiques Seyssel, 22, 200. C I R I A C K S , K. W. 1963. Permian and Eotriassic bivalves of the middle Rockies. Bulletin of the American Museum of Natural History, 125 (1), 1–100, pls 1–16. C O N R A D , T. A. 1842. Descriptions of new species of organic remains belonging to the Silurian, Devonian and Carboniferous systems of the United States. Journal of the Academy of Natural Sciences of Philadelphia, 8, 183–190. C O X , L. R. 1953. Lower Cretaceous Gastropoda, Lamellibranchia and Annelida from Alexander I Land (Falkland Islands dependencies). Falkland Islands Dependencies Survey, Scientific Reports, 4, 1–14, pls 1, 2. —— et al.1969. Bivalvia. 1–1224. In M O O R E , R. C. (ed.). Treatise on invertebrate paleontology, part N. Mollusca 6. The Geological Society of America, Boulder, and the University of Kansas, Lawrence. D A G Y S , A. S. and K A N Y G I N , A. V. 1996. The Triassic fauna of the north-east of Asia. Sibirskaj Isdatelskaj Firma Ran, Novosibirsk, 168 pp [in Russian]. D A L L , W. H. 1889. On the hinge of pelecypods and its development with an attempt toward a better subdivision of the group. American Journal of Science, 38, 445–462. D E F R A N C E , M. J. L. 1816. Avicule (Foss.). 141–142. In L E V R A U L T , F. G. (ed.). Dictionaire de Sciences Naturelles, Tome 3. Le Normant, Paris, 174 pp. D I C K I N S , J. M. 1957. Lower Permian pelecypods and gastropods from the Carnarvon Basin, Western Australia. Australian Bureau of Mineral Resources Bulletin, 41, 1–55. D O U V I L L É , H. 1912. Un essai de classification phylogénique des lamellibranches. Comptes Rendus hebdomadaires des Séances de l’Académie des Sciences Paris, 154, 1677–1681. F A N G , Z O NGJ I E 2010. Generic demarcation of Permo-Triassic Claraia-like species and their biogeographic significance. Alcheringa, 34, 161–178. F É R U S S A C , A. E. DE. 1822. Tableaux systématiques des animaux mollusques classés en familles naturelles, dans lesquels on a établi la concordance de tous les systèmes; suivis d’un prodrome général pour tous les mollusques terrestres ou fluviatiles, vivants ou fossiles. Bertrand, Paris, 111 pp. F I S C H E R , P. 1880–1887. Manuel de conchyliologie et de paléontologie conchyliologique. F. Savy, Paris, 1369 pp. F R E B O L D , H. 1931. Fauna, stratigraphische und palaeogeographische Verhältnisse des ostgrönländischen Zechsteins. Meddelelser om Grønland, 84 (3), 1–38, pls 1, 2. —— 1933. Weitere Beiträge zur Kenntnis des Oberen Paläozoikums Ostgrönlands. Meddelelser om Grønland, 84 (7), 1–61, pls 1–6. F R E C H , F. 1904. Neue Zweischaler und Brachiopoden aus der Bakonyer Trias. Abhandlung 2. 1–140. In H Ö L Z E L , E. (ed.). Resultate der wissenschaftlichen Erforschung des Balatonsees, Band 1, Teil 1, Anhang: Palaeontologie der Umgebung des Balatonsees, Band 2. Balaton-Ausschuss der Ungarischen Geographischen Gesellschaft, Wien, 140 pp. 1069 F U L D A , D. E. 1935. Handbuch der vergleichenden Stratigraphie Deutschlands, Band 7, Zechstein. Borntraeger, Berlin, 409 pp. F Ü R S I C H , F. T. 1980. Preserved life positions of some Jurassic bivalves. Paläontologische Zeitschrift, 54, 289–300. G A L F E T T I , T., B U C H E R , H., B R A Y A R D , A., H O C H U L I , P., W E I S S E R T , H., G U O D U N , K., A T U D O R E I , V. and G U E X , J. 2007a. Late Early Triassic climate change: insights from carbonate carbon isotopes, sedimentary evolution and ammonoid paleobiogeography. Palaeogeography, Palaeoclimatology, Palaeoecology, 243, 394–411. —— H O C H U L I , P. A., B R A Y A R D , A., B U C H E R , H., W E I S S E R T , H. and V I G R A N , O. V. 2007b. Smithian-Spathian boundary event: evidence for global climatic change in the wake of the end-Permian biotic crisis. Geology, 35, 291– 294. —— B U C H E R , H., O V T C H A R O V A , M., S C H A L T E G G E R , U., B R A Y A R D , A., B R Ü H W I L E R , T., G O U D E M A N D , N., W E I S S E R T , H., H O C H U L I , P. A., C O R D E Y , F. and K U A N G , G.-D. 2007c. Timing of the Early Triassic carbon cycle perturbations inferred from new U-Pb ages and ammonoid biochronozones. Earth and Planetary Science Letters, 258, 593–604. G I R T Y , G. H. 1927. Description of Carboniferous and Triassic fossils. In M A N S F I E L D , G. R. (ed.). Geography, geology, and mineral resources of part of southeastern Idaho. United States Geological Survey, Professional Paper, 152, 411–446, pls 22–25, 27, 28, 30. G O L D F U S S , A. 1833–1840. Petrefacta Germaniae. Abbildungen und Beschreibungen der Petrefacten Deutschlands und der angränzenden Länder, unter Mitwirkung des Herrn Grafen Georg zu Münster, herausgegeben von August Goldfuss. Zweiter Teil. Arnz and Co., Düsseldorf, 211 pp., 84 pls. G O L O N K A , J. and F O R D , D. 2000. Pangean (Late Carboniferous-Middle Jurassic) paleoenvironment and lithofacies. Palaeogeography, Palaeoclimatology, Palaeoecology, 161, 1–34. G O U D E M A N D , N., O R C H A R D , M., T A F F O R E A U , P., U R D Y , S., B R Ü H W I L E R , T., B U C H E R , H., B R A Y A R D , A. and G A L F E T T I , T. 2012. Early Triassic conodont clusters from South China: revision of the architecture of the 15-element apparatuses of the Gondolelloidea superfamily. Palaeontology, doi: 10.1111/j.1475-4983.2012.01174.x. G R A Y , J. E. 1824. Shells. Supplement to appendix, Perry’s voyage for the discovery of the north-west passage in the years 1819– 1820, Appendix 10, Zoology. J. Murray, London, 240–246. —— 1842. Synopsis of the contents of the British Museum. Fortyfourth edition, British Museum, London, 308 pp. —— 1847. A list of genera of Recent Mollusca, their synonyma and types. Proceedings of the Zoological Society of London, 15, 129–219. —— 1854. A revision of the arrangement of the families of bivalve shells (Conchifera). Annals and Magazine of Natural History, Series 2, 13, 408–418. G U Z H IW E I , H U A N G B A O Y U , C H E N C H U Z H E N , W E N SH I X UA N, M A Q I H O NG, L A N X I U , X U J U NTAO , L I U , LU, W A N G DE Y O U, Q U I RA NZH O N G, H U A N G ZH A O Q I , ZH A N G Z U O M I N G , C H E N J I N H U A and W U P EI LI 1976. Fossil Lamellibranchiata of China. Science Press, Beijing, 522 pp., 150 pls [in Chinese]. 1070 PALAEONTOLOGY, VOLUME 55 G U E X , J. 1978. Le Trias inférieur des Salt Ranges, Pakistan: problèmes biochronologiques. Eclogae geologicae Helvetiae, 71, 105–141. H A L L , J. 1858. Palaeontology of Iowa. 473–724, pls 1-29. In H A L L , J. and W H I T N E Y , J. D. (eds). Report on the geological survey of the state of Iowa: embracing the results of investigations made during portions of the years 1855, 56 and 57. Authority of the legislature of Iowa, Des Moines, 724 pp. —— and W H I T F I E L D , R. P. 1869. Preliminary notice of the lamellibranchiate shells of the Upper Helderberg, Hamilton and Chemung groups, with others from the Waverly Sandstones, Pt. 2. New York State Museum, Albany, 97 pp. —— —— 1877. Part II. Palaeontology. 198–302. In K I N G , C. (ed.) Annual report to the secretary of war on the U.S. geological exploration of the fortieth parallel, vol. 4. Government Printing Office, Washington D.C., 667 pp. H A L L A M , A. and W I G N A L L , P. B. 1997. Mass extinctions and their aftermath. Oxford University Press, Oxford ⁄ New York, 320 pp. H A M M E R , Ø., H A R P E R , D. A. T. and R Y A N , D. T. 2001. PAST: palaeontological statistics software package for education and data analyses. Palaeontologia Electronica, 4, 1–9 (http://palaeo-electronica.org/2001_1/past/issue1_01.htm). H A U T M A N N , M. 2001a. Taxonomy and phylogeny of cementing Triassic bivalves (Families Prospondylidae, Plicatulidae, Dimyidae and Ostreidae). Palaeontology, 44, 339– 373. —— 2001b. Die Muschelfauna der Nayband-Formation (Obertrias, Nor-Rhät) des östlichen Zentraliran. Beringeria, 29, 1–181. —— 2004. Early Mesozoic evolution of alivincular bivalve ligaments and its implications for the timing of the ‘‘Mesozoic marine revolution’’. Lethaia, 37, 165–172. —— 2006. Shell morphology and phylogenetic origin of oysters. Palaeogeography, Palaeoclimatology, Palaeoecology, 240, 668–671. —— 2010. The first scallop. Paläontologische Zeitschrift, 84, 317– 322. —— and N Ü T Z E L , A. 2005. First record of a heterodont bivalve (Mollusca) from the Early Triassic: palaeoecological significance and implications for the ‘Lazarus problem’. Palaeontology, 48, 1131–1138. —— B U C H E R , H., B R Ü H W I L E R , T., G O U D E M A N D , N., K A I M , A. and N Ü T Z E L , A. 2011. An unusually diverse mollusc fauna from the earliest Triassic of South China and its implications for benthic recovery after the end-Permian biotic crisis. Geobios, 44, 71–85. —— S M I T H , A. B., M C G O W A N , A. J. and B U C H E R , H. in press. Bivalves from the Olenekian (Early Triassic) of southwestern Utah: systematics and evolutionary significance. Journal of Systematic Palaeontology. H E W E I H O N G , F E N G , Q., W E L D O N , E. A., G U , S., M E N G , Y., Z H A N G , F. and W U , S. 2007. A Late Permian to Early Triassic bivalve fauna from the Dongpan section, southern Guangxi, South China. Journal of Paleontology, 81, 1009–1019. H E A L E Y , M. 1908. The fauna of the Napeng beds or the Rhaetic beds of Upper Burma. Memoirs of the Geological Survey of India, Palaeontologia Indica, new series, 2, 1–88, pls 1–9. H E R M A N N , E., H O C H U L I , P. A., M É H A Y , S., B U C H E R , H., B R Ü H W I L E R , T., H A U T M A N N , M., W A R E , D., R O O H I , G., U R - R E H M A N , K. and Y A S E E N , A. 2011a. Organic matter and palaeoenvironmental signals during the Early Triassic biotic recovery: the Salt Range and Surghar Range records. Sedimentary Geology, 237, 19–41. —— —— B U C H E R , H., B R Ü H W I L E R , T., H A U T M A N N , M., W A R E , D. and R O O H I , G. 2011b. Terrestrial ecosystems on North Gondwana in the aftermath of the end-Permian mass extinction. Gondwana Research, 20, 630–637. —— —— —— and R O O H I , G. in press. Early Triassic palynology of the Salt Range and Surghar Range, Pakistan. Review of Palaeobotany and Palynology. H E R T W I G , C. W. T. R. 1895. Lehrbuch der Zoologie (dritte Auflage). Fischer, Jena, 599 pp. H O C H U L I , P. A., H E R M A N N , E., V I R G A N , J. O., B U C H E R , H. and W E I S S E R T , H. 2010. Rapid demise and recovery of plant ecosystems across the end-Permian extinction event. Global and Planetary Change, 74, 144–155. I C H I K A W A , K. 1954. Early Neo-Triassic pelecypods from Iwai, near Itsukaichi, Tokyo prefecture. Japanese Journal of Geology and Geography, 25, 177–195. —— 1958. Zur Taxonomie und Phylogenie der triadischen Pteriidae (Lamellibranchiata) mit besonderer Berücksichtigung der Gattung Claraia, Eumorphotis, Oxytoma und Monotis. Palaeontographica, Abteilung A, 111, 131–212, pls 21–24. J A B L O N S K I , D. 1986. Causes and consequences of mass extinction: a comparative approach. 183–229. In E L L I O T T , D. K. (ed.). Dynamics of extinction. Wiley, New York, 294 pp. J E L E T Z K Y , J. A. 1963. Malayomaorica gen. nov. (Family Aviculopectinidae) from the Indo-Pacific Upper Jurassic; with comments on related forms. Palaeontology, 6, 148–160. J E N K S , J. F., B R A Y A R D , A., B R Ü H W I L E R , T. and B U C H E R , H. 2010. New Smithian (Early Triasic) ammonoids from Crittenden Springs, Elko County, Nevada: implications for taxonomy, biostratigraphy and biogeography. New Mexico Museum of Natural History and Science Bulletin, 48, 1–41. K A I M , A. 2009. Gastropods. In S H I G E T A , Y., Z A K H A R O V , YU. D., M A E D A , H. and P O P O V , A. M. (eds). The Lower Triassic system in the Abrek Bay area, south Primorye, Russia. National Museum of Nature and Science Monographs, 38, 141–156. —— and N Ü T Z E L , A. 2011. Dead bellerophontids walking – the short Mesozoic history of the Bellerophontoidea (Gastropoda). Palaeogeography, Palaeoclimatology, Palaeoecology, 308, 190–199. —— —— B U C H E R , H., B R Ü H W I L E R , T. and G O U D E M A N D , N. 2010. Early Triassic (Late Griesbachian) gastropods from South China (Shanggan, Guangxi). Swiss Journal of Geosciences, 103, 121–128. K I N G , W. 1848. A catalogue of the organic remains of the Permian rocks of Northumberland and Durham. The author, Newcastle-upon-Tyne, 16 pp. —— 1850. A monograph of the Permian fossils of England. Monograph of the Palaeontographical Society London, 37, 1– 258, pls 1–28. K I P A R I S O V A , L. D. 1938. The Lower Triassic pelecypods of the Ussuriland. Trudy Geologicheskogo Instituta, 7, 197–311 [In Russian]. WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN K L I P S T E I N , A. von 1845. Beiträge zur geologischen Kenntnis der östlichen Alpen. Heyer, Giessen, 311 pp. K O R O B K O V , I. A. 1954. Spravochnik i metodicheskoe rukovodstvo po tretichnym molliuskam. Plastinchatozhabernye (Handbook and methodical manual on Tertiary mollusks: Lamellibranchiates). Gostoptekhizdat, Leningrad, 444 pp, 96 pls [in Russian]. K U M A G A E , T. and N A K A Z A W A , K. 2009. Bivalves. In S H I G E T A , Y., Z A K H A R O V , YU. D., M A E D A , H. and P O P O V , A. M. (eds). The Lower Triassic system in the Abrek Bay area, south Primorye, Russia. National Museum of Nature and Science Monographs, 38, 156–173. K U M M E L , B. 1966. The Lower Triassic formations of the Salt Range and Trans-Indus Ranges, West Pakistan. Bulletin of the Museum of Comparative Zoology, Harvard University, 134, 361–429. —— and T E I C H E R T , C. 1966. Relations between the Permian and Triassic formations in the Salt Range and Trans-Indus Ranges, West Pakistan. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 125, 297–333. —— —— 1970. Stratigraphy and paleontology of the PermianTriassic boundary beds, Salt Range and Trans-Indus Ranges, West Pakistan. 1–110. In K U M M E L , B. and T E I C H E R T , C. (eds). Stratigraphic boundary problems: Permian and Triassic of West Pakistan. Department of Geology, University of Kansas, Special Publication, Lawrence, 474 pp. K U R U S H I N , N. I. 1987. Drevneishie triasovie dvuxstvorchatie molluski Yakutii. 99–110. In D A G Y S , A. S. (ed.) Borealnii trias. Nauka, Moscow, 119 pp. L E A C H , W. E. 1819. Descriptions des nouvelles espèces d’animaux découvertes par le vaisseau Isabelle dans un voyage au pôle boréal. Journal de Physique, de Chimie, d’Histoire Naturelle et des Arts, 88, 462–467. L E P S I U S , R. 1878. Das westliche Süd-Tirol, geologisch dargestellt. Verlag Wilhelm Hertz, Berlin, 375 pp. L E V I N T O N , J. S. 1996. Trophic group and the end-Cretaceous extinction: did deposit feeders have it made in the shade? Paleobiology, 22, 104–112. L I N N A E U S , C. 1758. Systema Naturae per Regna Tria Naturae, Secundum Classes, Ordines, Genera, Species, cum Characteribus, Differentiis, Synonymis, Locis. Tomus I. Editio Decima. Laurentius Salvius, Stockholm, 824 pp. L O G A N , A. 1967. The Permian Bivalvia of northern England. Monograph of the Palaeontographical Society London, 121, 1– 72, pls 1–10. M A R W I C K , J. 1935. Some new genera of the Myalinidae and Pteriidae of New Zealand. Transactions of the Royal Society of New Zealand, 65, 295–303. —— 1953. Divisions and faunas of the Hokonui System (Triassic and Jurassic). New Zealand Geological Survey, Paleontological Bulletin, 21, 1–141. M ’ C O Y , F. 1851–1855. Description of the British Palaeozoic fossils in the Geological Museum of the University of Cambridge. 1–644. In S E D G W I C K , A. and M ’ C O Y , F. (eds). A synopsis of the classification of the British Palaeozoic rocks, with a systematic description of the British Palaeozoic fossils in the Geological Museum of the University of Cambridge. Cambridge University Press, Cambridge, 661 pp. 1071 M E E K , F. B. and H A Y D E N , F. V. 1864. Palaeontology of the Upper Missouri. Smithsonian Contributions to Knowledge, 14, 1–135. M E N N I N G , M., G A S T , R., H A G D O R N , H., K Ä D I N G , K. C., S I M O N , T., S Z U R L I E S , M. and N I T S C H , E. 2005. Zeitskala für Perm und Trias in der Stratigraphischen Tabelle von Deutschland, 2002, zyklostratigraphische Kalibrierung der höheren Dyas und Germanischen Trias und das Alter der Stufen Roadium bis Rhaetium. Newsletters on Stratigraphy, 41, 173–210. M I L L E R , S. A. 1877. The American Palaeozoic fossils, a catalogue of the genera and species. The author, Cincinnati, 253 pp. —— 1889. North American geology and palaeontology. Western Methodist Book Concern, Cincinnati, 664 pp. M O R R I S , J. 1845. Conchifera. 270–278. In S T R Z E L E C K I , P. E. de (ed.). Physical description of New South Wales and Van Dieman’s Land. Longman, Brown and Co., London, 462 pp, 19 pls. M U S T E R , H. 1995. Taxonomie und Paläobiogeographie der Bakevelliidae (Bivalvia). Beringeria, 14, 1–161. N A K A Z A W A , K. 1959. Permian and Eo-Triassic Bakevellias from the Maizuru Zone, southwest Japan. Memoirs of the College of Science, University of Kyoto, 26, 193–213. —— 1961. Permian and Eo-Triassic Myophoriidae from the Maizuru zone, southwest Japan. Japanese Journal of Geology and Geography, 31, 49–62. —— 1977. On Claraia of Kashmir and Iran. Journal of the Palaeontological Society of India, 20, 191–204. —— 1996. Lower Triassic bivalves from the Salt Range Region, Pakistan. 207–229. In G U H A , P. K. S., A Y Y A S A M I , K., S E N G U P T A , S. and G H O S H , R. N. (eds). Gondwana Nine, Proceedings of the Ninth International Gondwana Symposium, Hyderabad, January 1994. A.A. Balkema, Rotterdam ⁄ Brookfield, 1290 pp. N E W E L L , N. D. 1965. Classification of the Bivalvia. American Museum Novitates, 2206, 1–25. —— and B O Y D , D. W. 1987. Iteration of ligament structures in pteriomorphian Bivalves. American Museum Novitates, 2875, 1–11. —— —— 1995. Pectinoid bivalves of the Permian-Triassic crisis. Bulletin of the American Museum of Natural History, 227, 1–95. —— —— 1999. A new Lower Triassic Permophorus from the central Rocky Mountains. American Museum Novitates, 3263, 1–5. N Ü T Z E L , A. 2005a. A new Early Triassic gastropod genus and the recovery of gastropods from the Permian ⁄ Triassic extinction. Acta Palaeontologica Polonica, 50, 19–24. —— 2005b. Recovery of gastropods in the Early Triassic. Comptes Rendus Palevol, 4, 501–515. —— and E R W I N , D. H. 2002. Battenizyga, a new Early Triassic gastropod genus with a discussion on the gastropod evolution at the Permian ⁄ Triassic boundary. Paläontologische Zeitschrift, 76, 21–26. O R B I G N Y , A. D’. 1844–1848. Paléontologie française. Description zoologique et géologique de tous les animaux mollusques et rayonnés fossiles de France. Terrains crétacés. Volume 3, Mollusques. Masson, Paris, 807 pp. O R C H A R D , M. J. 2007. Conodont diversity and evolution through the latest Permian and Early Triassic upheavals. 1072 PALAEONTOLOGY, VOLUME 55 Palaeogeography, Palaeoclimatology, Palaeoecology, 252, 93– 117. P A N , HUA-ZHANG, E R W I N D. H., N Ü T Z E L , A. and Z H U , XIANG-SHUI 2003. Jiangxispira, a new gastropod genus from the Early Triassic of China with remarks on the phylogeny of the Heterostropha at the Permian ⁄ Triassic boundary. Journal of Paleontology, 77, 44–49. P A Y N E , J. L., L E H R M A N N , D. J., W E I , J. Y., O R C H A R D , M. J., S C H R A G , D. P. and K N O L L , A. H. 2004. Large perturbations of the carbon cycle during recovery from the endPermian extinction. Science, 305, 506–509. P H I L I P P I , E. 1898. Die Fauna des unteren TrigonodusDolomits vom Hühnerfeld bei Schwieberdingen und des sogenannten ‘‘Cannstatter Kreidemergels’’. Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg, 1898, 145–224. PJRG (PAKISTANI JAPANESE RESEARCH GROUP) 1985. Permian and Triassic systems in the Salt Range and Surghar Range, Pakistan. 221–312. In N A K A Z A W A , K. and D I C K I N S , J. M. (eds). The Tethys: her paleogeography and paleobiogeography from Paleozoic to Mesozoic. Tokai University Press, Tokyo, Japan, 317 pp. P O M P E C K J , J. F. 1901. Über Aucellen und Aucellen-ähnliche Fromen. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, Beilage-Band, 14, 319–368. P O S E N A T O , R. 2008. Patterns of bivalve biodiversity from Early to Middle Triassic in the Southern Alps (Italy): regional vs. global events. Palaeogeography, Palaeoclimatology, Palaeoecology, 261, 145–159. P T S C H E L I N C E V A , V. F. 1960. Family Prospondylidae fam. nov. 86–87. In E B E R Z I N , A. G. (ed.). Fundamentals of palaeontology. Molluscs-Loricata, Bivalvia, Scaphopoda. Isdatel’stvo Akademii Nauk SSSR, Moscow, 300 pp. [In Russian]. R A F I N E S Q U E , C. S. 1815. Analyse de la nature ou tableau de l’univers et des corps organisés. Jean Barravecchia, Palermo, 223 pp. R E E D , F. R. C. 1932. New fossils from the agglomeratic slate of Kashmir. Memoirs of the Geological Survey of India, Palaeontologia Indica, new series, 20, 1–79, pls 1–13. R E P I N , Yu. S. 1996. New Late Triassic bivalves from Iran and a taxonomy of the superfamily Spondylacea. Paleontological Journal, 30, 363–369. S C H L O T H E I M , E. F. von. 1820. Die Petrefactenkunde auf ihrem jetzigen Standpunkte durch die Beschreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzenreichs der Vorwelt erläutert. Becker’sche Buchhandlung, Gotha, 437 pp. S C H U B E R T , J. K. and B O T T J E R , D. J. 1995. Aftermath of the Permian-Triassic mass extinction event: paleoecology of Lower Triassic carbonates in the western USA. Palaeogeography, Palaeoclimatology, Palaeoecology, 116, 1–39. S E I L A C H E R , A. 1954. Ökologie der triassischen Muschel Lima lineata (Schloth.) und ihrer Epöken. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte, 1954 (1), 163–183. S H A J I NGE NG 1995. Bivalves. 82–115, 149–151. In S H A JI N GEN G (ed.), Palaeontology of the Hohxil Region, Qinghai. Science Press, Beijing, 177 pp, 50 pls. [In Chinese with English abstract]. —— and F Ü R S I C H , F. T. 1994. Bivalve faunas of eastern Heilongjiang, northeastern China. II. The Late Jurassic and Early Cretaceous buchiid fauna. Beringeria, 12, 1–93. —— and G R A N T - M A C K I E , J. A. 1996. Late Permian to Miocene bivalve assemblages from Hohxil, Qinghai-Xizang Plateau, China. Journal of the Royal Society of New Zealand, 26, 429–455. S H E E H A N , P. M. and H A N S E N , T. A. 1986. Detritus feeding as a buffer to extinction at the end of the Cretaceous. Geology, 14, 868–870. S M I T H , A. G., S M I T H , D. G. and F U N N E L L , B. M. 1994. Atlas of Mesozoic and Cenozoic coastlines. Cambridge University Press, Cambridge, 109 pp. S O W E R B Y , J. 1812–1814. The mineral conchology of Great Britain; or coloured figures and description of those remains of testaceous animals or shells which have been preserved at various times and depths in the earth, Volume 1. Arding and Meredith, London, 236 pp. S P A T H , L. F. 1935. Additions to the Eotriassic invertebrate fauna of East Greenland. Meddelelser om Grønland, 98 (2), 1– 115, pls 1–23. S T A N L E Y , S. M. 1972. Functional morphology and evolution of byssally attached bivalve mollusks. Journal of Paleontology, 46, 165–212. S T E N Z E L , H. B. 1971. Oysters. N953–N1224. In M O O R E , R. C. (ed.). Treatise on invertebrate paleontology, part N, Mollusca 6, Bivalvia 3. The Geological Society of America, Boulder and The University of Kansas Press, Lawrence, 271 pp. T Ë M K I N , I. and P O J E T A , J. J. 2010. Cassiavellia galtarae, new species, new genus: a new Permian bivalve and its significance for pterioidean systematics. Journal of Paleontology, 84, 1152–1176. T E P P N E R , W. von 1922. Lamellibranchia Tertiaria, Anisomyaria II. 67–296. In D I E N E R , C. (ed.). Fossilium catalogus 1, 15, W. Junk, Berlin, 296 pp. T R E C H M A N N , C. T. 1918. The Trias of New Zealand. Quarterly Journal of the Geological Society London, 73, 165–246. T U R N E R , R. D. and R O S E W A T E R , J. 1958. The family Pinnidae in the western Atlantic. Johnsonia, 3, 285–326. V O K E S , H. E. 1967. Genera of the Bivalvia: a systematic and bibliographic catalogue. Bulletins of American Paleontology, 51, 105–394. W A A G E N , W. 1879. Salt-Range fossils, Vol. 1: productus limestone fossils, Pisces-Cephalopoda. Memoirs of the Geological Survey of India, Palaeontologia Indica, 13 (1), 1–72, pls 1–15. —— 1880. Salt Range fossils, Vol. 1: productus limestone fossils, Gastropoda. Memoirs of the Geological Survey of India, Palaeontologia Indica, 13, 73–184, pls 7–16. —— 1881. Salt Range fossils, Vol. 1: productus limestone fossils, Pelecypoda. Memoirs of the Geological Survey of India, Palaeontologia Indica, 13, 185–328, pls 17–24. —— 1882–1884. Salt Range fossils, Vol. 1: productus limestone fossils, Brachiopoda. Memoirs of the Geological Survey of India, Palaeontologia Indica, 13, 329–728, pls 25–86. —— 1891. Salt Range fossils, Vol. 2: geological results. Memoirs of the Geological survey of India, Palaeontologia Indica, 13, 89– 242. WASMER ET AL.: EARLY TRIASSIC BIVALVES FROM PAKISTAN —— 1895. Salt-Range fossils, Vol. 2: fossils from the Ceratite Formation. Pisces-Ammonoidea (Cephalopoda). Memoirs of the Geological Survey of India, Palaeontologia Indica, 13 (2), 1– 323, pls 1–40. W A L L E R , T. R. 1978. Morphology, morphoclines and a new classification of the Pteriomorpha (Mollusca: Bivalvia). Philosophical Transactions of the Royal Society of London B, 284, 345–365. —— and S T A N L E Y , G. D. 2005. Middle Triassic pteriomorphian Bivalvia (Mollusca) from the New Pass Range, west-central Nevada: systematics, biostratigraphy, paleoecology and paleobiogeography. The Palaeontological Society Memoir, 61, 1–64. W A R E , D., J E N K S , J., H A U T M A N N , M. and B U C H E R , H. 2011. Dienerian (Early Triassic) ammonoids from the Candelaria Hills (Nevada, USA) and their significance for palaeobiogeography and palaeoceanography. Swiss Journal of Geosciences, 104, 161–181. W A T E R H O U S E , J. B. 1960. Some Carnian Pelecypoda from New Zealand. Transactions of the Royal Society of New Zealand, 88, 425–442, pls 19–25. —— 1978. Permian Brachiopoda and Mollusca from north-west Nepal. Palaeontographica, Abteilung A, 160, 1–175, pls 1–26. —— 1980. A new bivalve species (Buchiidae) from the Early Triassic of New Zealand. Alcheringa, 4, 1–10. —— 1982. Permian Pectinacea and Limacea (Bivalvia) from New Zealand. New Zealand Geological Survey, Paleontological Bulletin, 49, 1–75, pls 1–25. —— 2001. Late Paleozoic Brachiopoda and Mollusca chiefly from Wairaki Downs, New Zealand, with notes on Scyphozoa and Triassic ammonoids and new classifications of Linoproductoidea (Brachiopoda) and Pectinida (Bivalvia). Earthwise, 3, 1–196, pls 1–10. —— 2008. Aspects of the evolutionary record for fossils of the bivalve subclass Pteriomorphia Beurlen. Earthwise, 8, 1–219. 1073 W H I T F I E L D , R. P. 1885. Brachiopoda and Lamellibranchiata of the Raritan clays and greensand marls of New Jersey. US Geological Survey Monographs, 9, 1–338. W I L C K E N S , R. 1909. Paläontologische Untersuchung triadischer Faunen aus der Umgebung von Predazzo im Südtirol. Verhandlungen des naturhistorisch-medizinischen Vereins Heidelberg, neue Folge, 10, 81–231. W I S S M A N N , H. L. 1841. Beiträge zur Geognosie und Petrefactenkunde des südöstlichen Tirols. 1–24. In W I S S M A N N , H. L., M Ü N S T E R , G. and GR AF ZU (eds). Beiträge zur Petrefactenkunde, 152 pp, pls 1–16. W I T T E N B U R G , P. von. 1908. Beiträge zur Kenntnis der Werfener Schichten Südtirols. Geologische und Paläontologische Abhandlungen, neue Folge, 8, 251–289. —— 1909. Einige Lamellibranchiata der Salt-Range, mit Berücksichtigung der Lamellibranchiata des Süd-Ussuri-Gebiets. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, 1909, 6–13, pls 2, 3. W Ö H R M A N N , S. von. 1889. Die Fauna der sogenannten Cardita und Raibler Schichten in den Alpen Nordtirols und in den Bayerischen Alpen. Jahrbuch der kaiserlichköniglichen Geologischen Reichsanstalt, 39 (1), 180–258, pls 1–5. Y E H A R A , S. 1927. The Lower Triassic cephalopod and bivalve fauna of Shikoku. The Japanese Journal of Geology and Geography, 5, 135–172. Z A K H A R O V , V. A. 1981. Buchiidae and biostratigraphy of the boreal Upper Jurassic and Neocomian. Journal of Geology and Geophysics (Moscow, Nauka), 458, 1–270[In Russian]. Z I T T E L , K. A. von. 1881–1885. Handbuch der Palaeontologie, Band 2, 1. Abteilung, Palaeozoologie. R. Oldenburg, München and Leipzig, 893 pp.