- Department of Earth Sciences
Lower Mount Joy
Durham University
DH1 3LE - 0191 334 2320
Martin R Smith
Durham University, Department of Earth Sciences, Faculty Member
Research Interests:
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Research Interests:
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The present-day distribution of velvet worms corresponds neatly to the ancient supercontinent Gondwana — except for a puzzling outpost in southeast Asia. Jaw-dropping new fossil material now establishes when and how peripatid... more
The present-day distribution of velvet worms corresponds neatly to the ancient supercontinent Gondwana — except for a puzzling outpost in southeast Asia. Jaw-dropping new fossil material now establishes when and how peripatid onychophorans reached this isolated spot.
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The fossil record paints a thin picture of early terrestrial life. Useful diagnostic features are rare in the organic-walled fossils of the first land colonizers, and at first glance the Silurian–Devonian Tortotubus protuberans seems no... more
The fossil record paints a thin picture of early terrestrial life. Useful diagnostic features are rare in the organic-walled fossils of the first land colonizers, and at first glance the Silurian–Devonian Tortotubus protuberans seems no exception. Now, new material from New York, Gotland and Scotland reveals the ontogenesis and affinity of this problematic organism. Its filamentous early stages (previously referred to Ornatifilum lornensis) demonstrate simple septal perforations and a bilayered cell wall; threads of entwined filaments, bounded by an elaborately sculptured surface, arose via the retrograde growth and subsequent proliferation of secondary branches. This morphology and pattern of growth together indicate an affinity with the ‘higher’ fungi (Dikarya) and document the formation of differentiated mycelium. The presence of complex mycelial fossils in the earliest Silurian corroborates the likely contribution of fungi to the colonization of land and the establishment of modern sedimentological systems; their rise seemingly accompanied the diversification of early embryophytes and the vegetation of the terrestrial biosphere.
Research Interests:
Tabulation of fossil priapulid diversity, incorporating (a) valid and (b) invalid priapulid taxa
Tabulation of fossil priapulid diversity, incorporating (a) valid and (b) invalid priapulid taxa
The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land‐plant, despite the absence of a convincing modern analogue. Exceptionally well‐preserved nematophyte cuticle from the Late... more
The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land‐plant, despite the absence of a convincing modern analogue. Exceptionally well‐preserved nematophyte cuticle from the Late Silurian Burgsvik Sandstone Formation, Gotland provides additional insight into the organism’s anatomy, phylogenetic affiliations and ecology. Because this material exhibits additional characters not present in the type material we assign it to Nematothallopsis gotlandii gen. et sp. nov. The organism was constituted of a close‐packed layer of palisade‐like filaments covered by a cuticle that bears a characteristic pseudocellular pattern on its inner surface. Apertures in this cuticle are often encircled by a ring of multicellular filaments, which are sometimes associated with spheroidal, spore‐like entities. In the light of the conspicuous similarity of the palisade layers to the pseudoparenchymatous tissue of coralline red algae, and of the filamen...
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Wiwaxiids are a problematic group of scale-covered lophotrochozoans known from Cambrian Stages 3–5. Their imbricating dorsal scleritome of leaf-like scales has prompted comparison with various annelids and molluscs, and has been used as a... more
Wiwaxiids are a problematic group of scale-covered lophotrochozoans known from Cambrian Stages 3–5. Their imbricating dorsal scleritome of leaf-like scales has prompted comparison with various annelids and molluscs, and has been used as a template to reconstruct the articulation pattern of isolated Small Shelly Fossils. The first articulated specimens of Wiwaxia from the Cambrian Stage 3 Chengjiang Konservat-Lagerstätte show that the Wiwaxia scleritome comprised nine equivalent transverse rows associated with outgrowths of soft tissue, but did not possess a separate zone of anterior sclerites. This serial construction is fundamentally incompatible with the circumferential disposition of sclerites in early molluscs, but does closely resemble the armature of certain annelids. A deep homology with the annelid scleritome must be reconciled with Wiwaxia’s mollusc-like mouthparts and foot; together these point to a deep phylogenetic position, close to the common ancestor of annelids and molluscs.
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The Palaeozoic form-taxon Lobopodia encompasses a diverse range of soft-bodied ‘legged worms’ known from exceptional fossil deposits1, 2, 3, 4, 5, 6, 7, 8, 9. Although lobopodians occupy a deep phylogenetic position within Panarthropoda,... more
The Palaeozoic form-taxon Lobopodia encompasses a diverse range of soft-bodied ‘legged worms’ known from exceptional fossil deposits1, 2, 3, 4, 5, 6, 7, 8, 9. Although lobopodians occupy a deep phylogenetic position within Panarthropoda, a shortage of derived characters obscures their evolutionary relationships with extant phyla (Onychophora, Tardigrada and Euarthropoda)2, 3, 5, 10, 11, 12, 13, 14, 15. Here we describe a complex feature in the terminal claws of the mid-Cambrian lobopodian Hallucigenia sparsa—their construction from a stack of constituent elements—and demonstrate that equivalent elements make up the jaws and claws of extant Onychophora. A cladistic analysis, informed by developmental data on panarthropod head segmentation, indicates that the stacked sclerite components in these two taxa are homologous—resolving hallucigeniid lobopodians as stem-group onychophorans. The results indicate a sister-group relationship between Tardigrada and Euarthropoda, adding palaeontological support to the neurological16, 17 and musculoskeletal18, 19 evidence uniting these disparate clades. These findings elucidate the evolutionary transformations that gave rise to the panarthropod phyla, and expound the lobopodian-like morphology of the ancestral panarthropod.
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"The soft-bodied Cambrian organism Wiwaxia poses a taxonomic conundrum. Its imbricated dorsal scleritome suggests a relationship with the polychaete annelid worms, whereas its mouthparts and naked ventral surface invite comparison with... more
"The soft-bodied Cambrian organism Wiwaxia poses a taxonomic conundrum. Its imbricated dorsal scleritome suggests a relationship with the polychaete annelid worms, whereas its mouthparts and naked ventral surface invite comparison with the molluscan radula and foot.
476 new and existing specimens from the 505 million year old Burgess Shale cast fresh light on Wiwaxia’s sclerites and scleritome. My observations illuminate the diversity within the genus, and demonstrate that Wiwaxia did not undergo discrete moult stages: rather, its scleritome developed gradually, with piecewise addition and replacement of individually-secreted sclerites.
I recognize a digestive tract and creeping foot in Wiwaxia, solidifying its relationship with the contemporary Odontogriphus. Similarities between the scleritomes of Wiwaxia, halkieriids, Polyplacophora and Aplacophora hint that the taxa are related. A molluscan affinity is robustly established, and Wiwaxia provides a good fossil proxy for the ancestral aculiferan – and perhaps molluscan – body plan."
476 new and existing specimens from the 505 million year old Burgess Shale cast fresh light on Wiwaxia’s sclerites and scleritome. My observations illuminate the diversity within the genus, and demonstrate that Wiwaxia did not undergo discrete moult stages: rather, its scleritome developed gradually, with piecewise addition and replacement of individually-secreted sclerites.
I recognize a digestive tract and creeping foot in Wiwaxia, solidifying its relationship with the contemporary Odontogriphus. Similarities between the scleritomes of Wiwaxia, halkieriids, Polyplacophora and Aplacophora hint that the taxa are related. A molluscan affinity is robustly established, and Wiwaxia provides a good fossil proxy for the ancestral aculiferan – and perhaps molluscan – body plan."
We recently redescribed the Middle Cambrian organism Nectocaris pteryx, known from 92 specimens from the Burgess Shale (Smith & Caron 2010). In contrast to the single, ill-preserved specimen that formed the basis to earlier studies, this... more
We recently redescribed the Middle Cambrian organism Nectocaris pteryx, known from 92 specimens from the Burgess Shale (Smith & Caron 2010). In contrast to the single, ill-preserved specimen that formed the basis to earlier studies, this new material allowed us to identify new features consistent with a cephalopod affinity. But Nectocaris clearly lies outside the cephalopod crown-group, not least because it lacks a mineralized shell – a plesiomorphy of the crowngroup Cephalopoda. Mazurek & Zaton´ (2011) object to our classification of Nectocaris in the cephalopod stem lineage because of perceived differences between Nectocaris and crown-group cephalopods. As the authors themselves state, such differences are tangential to Nectocaris’s affinity. Rather, synapomorphies hold the key to classifying Cambrian oddballs: but Nectocaris shares no homologous characters with the anomalocaridids (stem-group Arthropoda), where the authors propose it belongs. Mazurek and Zaton´ present no meaningful challenge or alternative to Nectocaris’s interpretation as a ‘primitive’ – that is, stem-group – cephalopod.
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Nectocaridids are soft-bodied early to middle Cambrian organisms known from Burgess Shale-type deposits in Canada, China, and Australia. Originally described as unrelated species, they have recently been interpreted as a clade; their... more
Nectocaridids are soft-bodied early to middle Cambrian organisms known from Burgess Shale-type deposits in Canada, China, and Australia. Originally described as unrelated species, they have recently been interpreted as a clade; their flexible tentacles, camera-type eyes, lateral fins, internal gills, axial cavity, and funnel point to a relationship with the cephalopods. However, aspects of this reinterpretation, including the relevance of the group to cephalopod evolution, have been called into question.
Here, I examine new and existing nectocaridid material, including a large new form that may represent a sexual dimorph of Nectocaris pteryx. Differences between existing taxa largely represent taphonomic variation between sites and specimens—which provides further constraint on the organisms' anatomy. I revise the morphology of the tentacles and fins, and describe mouthparts and phosphatized gills for the first time. A mathematical analysis supports the presence of the earliest known camera-type eyes, and fluid mechanical considerations suggest that the funnel is optimized for efficient jet propulsion in a low Reynolds number flow regime.
Nectocaridids closely resemble coleoid cephalopods, but a position deeper within Cephalopoda raises fewer stratigraphic challenges. Whether its coleoid-like construction reflects common ancestry or profound convergence, the Nectocaris body plan adds substantially to Cambrian disparity, demonstrating the rapid colonization of nektobenthic niches after the Cambrian explosion.
Here, I examine new and existing nectocaridid material, including a large new form that may represent a sexual dimorph of Nectocaris pteryx. Differences between existing taxa largely represent taphonomic variation between sites and specimens—which provides further constraint on the organisms' anatomy. I revise the morphology of the tentacles and fins, and describe mouthparts and phosphatized gills for the first time. A mathematical analysis supports the presence of the earliest known camera-type eyes, and fluid mechanical considerations suggest that the funnel is optimized for efficient jet propulsion in a low Reynolds number flow regime.
Nectocaridids closely resemble coleoid cephalopods, but a position deeper within Cephalopoda raises fewer stratigraphic challenges. Whether its coleoid-like construction reflects common ancestry or profound convergence, the Nectocaris body plan adds substantially to Cambrian disparity, demonstrating the rapid colonization of nektobenthic niches after the Cambrian explosion.
Research Interests:
"Rindal and Brower (2011) present the surprising conclusion that likelihood and parsimony criteria produce the same “optimal” tree topologies, based on a meta-analysis of studies from Molecular Phylogenetics and Evolution. I enlarged... more
"Rindal and Brower (2011) present the surprising
conclusion that likelihood and parsimony criteria produce the same “optimal” tree topologies, based on a
meta-analysis of studies from Molecular Phylogenetics
and Evolution. I enlarged this dataset, which is heavily
biased towards low taxonomic levels, by adding studies
that addressed relationships between higher taxa
(Table S1). Whereas parsimony and likelihood tree
topologies are often identical at species level, major
differences occurred in one-third of studies above the
familial level (Fig. 1)...."
conclusion that likelihood and parsimony criteria produce the same “optimal” tree topologies, based on a
meta-analysis of studies from Molecular Phylogenetics
and Evolution. I enlarged this dataset, which is heavily
biased towards low taxonomic levels, by adding studies
that addressed relationships between higher taxa
(Table S1). Whereas parsimony and likelihood tree
topologies are often identical at species level, major
differences occurred in one-third of studies above the
familial level (Fig. 1)...."
Research Interests:
The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land-plant, despite the absence of a convincing modern analogue. Exceptionally well-preserved nematophyte cuticle from the Late... more
The thalloid carbonaceous fossil Nematothallus Lang, 1937, has been widely interpreted as an early Palaeozoic land-plant, despite the absence of a convincing modern analogue. Exceptionally well-preserved nematophyte cuticle from the Late Silurian Burgsvik Sandstone Formation, Gotland provides additional insight into the organism’s anatomy, phylogenetic affiliations and ecology. Because this material exhibits additional characters not present in the type material we assign it to Nematothallopsis gotlandii gen. et sp. nov. The organism was constituted of a close-packed layer of palisade-like filaments covered by a cuticle that bears a characteristic pseudocellular pattern on its inner surface. Apertures in this cuticle are often encircled by a ring of multicellular filaments, which are sometimes associated with spheroidal, spore-like entities. In the light of the conspicuous similarity of the palisade layers to the pseudoparenchymatous tissue of coralline red algae, and of the filament-fringed apertures to their reproductive conceptacles, we reconstruct the Nematothallopsis organism as an extinct rhodophyte and re-evaluate the putative terrestrial habit of cuticular nematophytes in general.
Research Interests:
"Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian ‘explosion’. However, the rarity of these fossil deposits... more
"Burgess Shale-type deposits are renowned for their exquisite preservation of
soft-bodied organisms, representing a range of animal body plans that evolved
during the Cambrian ‘explosion’. However, the rarity of these fossil deposits
makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive
chronicle of early animal evolution—but are difficult to interpret in the absence
of corresponding whole-body fossils. Here, we provide new observations on the
dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia
sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a
distinctive scaly microstructure and layered (cone-in-cone) construction that
together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus,
RushtonitesandRhombocorniculum—as spines ofHallucigenia-type lobopodians.
Hallucigeniids are thus revealed as an important and widespread component of
disparate Cambrian communities from late in the Terreneuvian (Cambrian
Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in
the latest Cambrian may be partly taphonomic. The cone-in-cone construction
of hallucigeniid sclerites is shared with the sclerotized cuticular structures ( jaws
and claws) in modern onychophorans. More generally, our results emphasize
the reciprocal importance and complementary roles of Burgess Shale-type
fossils and isolated microfossils in documenting early animal evolution."
soft-bodied organisms, representing a range of animal body plans that evolved
during the Cambrian ‘explosion’. However, the rarity of these fossil deposits
makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive
chronicle of early animal evolution—but are difficult to interpret in the absence
of corresponding whole-body fossils. Here, we provide new observations on the
dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia
sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a
distinctive scaly microstructure and layered (cone-in-cone) construction that
together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus,
RushtonitesandRhombocorniculum—as spines ofHallucigenia-type lobopodians.
Hallucigeniids are thus revealed as an important and widespread component of
disparate Cambrian communities from late in the Terreneuvian (Cambrian
Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in
the latest Cambrian may be partly taphonomic. The cone-in-cone construction
of hallucigeniid sclerites is shared with the sclerotized cuticular structures ( jaws
and claws) in modern onychophorans. More generally, our results emphasize
the reciprocal importance and complementary roles of Burgess Shale-type
fossils and isolated microfossils in documenting early animal evolution."
Research Interests:
Wiwaxia is a bizarre metazoan that has been interpreted as a primitive mollusc and as a polychaete annelid worm. Extensive material from the Burgess Shale provides a detailed picture of its morphology and ontogeny, but the fossil record... more
Wiwaxia is a bizarre metazoan that has been interpreted as a primitive mollusc and as a polychaete annelid worm. Extensive material from the Burgess Shale provides a detailed picture of its morphology and ontogeny, but the fossil record outside this lagerstätte is scarce, and complete wiwaxiids are particularly rare. Here we report small articulated specimens of Wiwaxia foliosa sp. nov. from the Xiaoshiba fauna (Cambrian Stage 3, Hongjingshao Formation, Kunming, south China). Although spines are absent, the fossils' sclerites – like those of W. corrugata – are symmetrically arranged in five distinct zones. They form rows across the body, and were individually added and shed throughout growth to retain an approximately symmetrical body shape. Their development pattern suggests a molluscan affinity. The basic body plan of wiwaxiids is fundamentally conserved across two continents through Cambrian Stages 3–5 – revealing morphological stasis in the wake of the Cambrian explosion.
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Research Interests:
The Middle Cambrian lophotrochozoans Odontogriphus omalus and Wiwaxia corrugata have been interpreted as stem-group members of either the Mollusca, the Annelida, or a group containing Mollusca + Annelida. The case for each classification... more
The Middle Cambrian lophotrochozoans Odontogriphus omalus and Wiwaxia corrugata have been interpreted as stem-group members of either the Mollusca, the Annelida, or a group containing Mollusca + Annelida. The case for each classification rests on the organisms' unusual mouthparts, whose two to three tooth-rows resemble both the molluscan radula and the jaws of certain annelid worms. Despite their potential significance, these mouthparts have not previously been described in detail. This study examined the feeding apparatuses of over 300 specimens from the 505-million-year-old Burgess Shale, many of which were studied for the first time. Rather than denticulate plates, each tooth row comprises a single axial tooth that is flanked on each side by eight to 16 separate shoehorn-shaped teeth. Tooth rows sat on a grooved basal tongue, and two large lobes flanked the apparatus. New observations—the shape, distribution and articulation of the individual teeth, and the mouthparts' mode of growth—are incompatible with an annelid interpretation, instead supporting a classification in Mollusca. The ancestral molluscan radula is best reconstructed as unipartite with a symmetrical medial tooth, and Odontogriphus and Wiwaxia as grazing deposit-feeders.
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Palaeoscolecid worms are a ubiquitous group of Early Palaeozoic ecdysozoans that are curiously lacking in the archetypal Cambrian Lagerstätten, the Burgess Shale. Here I describe Scathascolex minor gen. et sp. nov, the first unequivocal... more
Palaeoscolecid worms are a ubiquitous group of Early Palaeozoic ecdysozoans that are curiously lacking in the archetypal Cambrian Lagerstätten, the Burgess Shale. Here I describe Scathascolex minor gen. et sp. nov, the first unequivocal palaeoscolecid from this site. Scathascolex is armoured with simple Hadimopanella-like plates, but lacks smaller platelets, pointing to a close affinity with the Palaeoscolecida sensu stricto. Neither preservational nor environmental factors account for the scarcity of palaeoscolecids in the Burgess Shale, which presumably represents an ecological phenomenon.
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The stem-group priapulid Ottoia Walcott, 1911, is the most abundant worm in the mid-Cambrian Burgess Shale, but has not been unambiguously demonstrated elsewhere. High-resolution electron and optical microscopy of macroscopic Burgess... more
The stem-group priapulid Ottoia Walcott, 1911, is the most abundant worm in the mid-Cambrian Burgess Shale, but has not been unambiguously demonstrated elsewhere. High-resolution electron and optical microscopy of macroscopic Burgess Shale specimens reveals the detailed anatomy of its robust hooks, spines and pharyngeal teeth, establishing the presence of two species: Ottoia prolifica Walcott, 1911, and Ottoia tricuspida sp. nov. Direct comparison of these sclerotized elements with a suite of shale-hosted mid-to-late Cambrian microfossils extends the range of ottoiid priapulids throughout the middle to upper Cambrian strata of the Western Canada Sedimentary Basin. Ottoiid priapulids represented an important component of Cambrian ecosystems: they occur in a range of lithologies and thrived in shallow water as well as in the deep-water setting of the Burgess Shale. A wider survey of Burgess Shale macrofossils reveals specific characters that diagnose priapulid sclerites more generally, establishing the affinity of a wide range of Small Carbonaceous Fossils and demonstrating the prominent role of priapulids in Cambrian seas.
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The robust spines and sclerites of the early to middle Cambrian ‘mollusc’ Wiwaxia are ubiquitous in suitably-preserved deposits – but are strikingly absent from the Chengjiang Lagerstätten (Cambrian Stage 3, Yunnan Province, southwest... more
The robust spines and sclerites of the early to middle Cambrian ‘mollusc’ Wiwaxia are
ubiquitous in suitably-preserved deposits – but are strikingly absent from the
Chengjiang Lagerstätten (Cambrian Stage 3, Yunnan Province, southwest China).
Here we provide the first record of Wiwaxia sclerites from this rich deposit, extending
the record of the genus to earliest Cambrian Series 2. This reinforces the cosmopolitan
distribution of this iconic Cambrian lophotrochozoan and demonstrates the strong
faunal continuity that unites distant Cambrian Lagerstätten.
ubiquitous in suitably-preserved deposits – but are strikingly absent from the
Chengjiang Lagerstätten (Cambrian Stage 3, Yunnan Province, southwest China).
Here we provide the first record of Wiwaxia sclerites from this rich deposit, extending
the record of the genus to earliest Cambrian Series 2. This reinforces the cosmopolitan
distribution of this iconic Cambrian lophotrochozoan and demonstrates the strong
faunal continuity that unites distant Cambrian Lagerstätten.