Mark Loewen

This paper reports a new assemblage of social insect ichnofossils from the Brushy Basin Member of the Upper Jurassic Morrison Formation near Green River, Utah. At least seven distinct nests are visible in the locality horizon, identifiable at the outcrop scale by loci of anastomosing, and orthogonally connected hor-izontal burrows and vertical shafts. A boulder-sized block from the in situ horizon has eroded and rolled downhill, revealing the ventral aspect of the nest, showing a view of the overall nest architecture. Burrow and shaft clusters are organized into mega-galleries which have branching arms and ovate, bulbous cham-bers. The organization of distinct trace morphologies is consistent with ethological complexity of the social insects. A small sample was collected and analyzed by serial sectioning and petrographic thin sectioning to observe small-scale morphological features. Centimeter-scale analysis shows chamber, gallery, and burrow walls have complex topography. Pebble-si...

Allosaurus is one of the best known theropod dinosaurs from the Jurassic and a crucial taxon in phylogenetic analyses. On the basis of an in-depth, firsthand study of the bulk of Allosaurus specimens housed in North American institutions, we describe here a new theropod dinosaur from the Upper Jurassic Morrison Formation of Western North America, Allosaurus jimmadseni sp. nov., based upon a remarkably complete articulated skeleton and skull and a second specimen with an articulated skull and associated skeleton. The present study also assigns several other specimens to this new species, Allosaurus jimmadseni, which is characterized by a number of autapomorphies present on the dermal skull roof and additional characters present in the postcrania. In particular, whereas the ventral margin of the jugal of Allosaurus fragilis has pronounced sigmoidal convexity, the ventral margin is virtually straight in Allosaurus jimmadseni. The paired nasals of Allosaurus jimmadseni possess bilateral...

Caddisfly larvae construct underwater protective cases using surrounding materials, thus providing information on environmental conditions in both modern and ancient systems. Microbial bioherms associated with caddisfly cases are found in the Berriassian-Hauterivian (~140-130 Ma) Shinekhudag Formation of Mongolia, and yield new insights into aspects of lacustrine paleoecosystems and paleoenvironments. This formation contains the earliest record of plant-armored caddisfly cases and a rare occurrence of microbial-caddisfly association from the Mesozoic. The bioherms are investigated within the context of stratigraphic correlations, depositional environment interpretations, and basin-evolution models of the sedimentary fill. The bioherms form 0.5-2.0 m diameter mound-shaped bodies and are concentrated within a single, oil shale-bound stratigraphic interval. Each bioherm is composed of up to 40% caddisfly cases along with stromatolites of millimeter-scale, micritic laminations. Petrogra...

The Upper Cretaceous (middle-late Campanian) Wahweap Formation of southern Utah contains the oldest diagnostic evidence of ceratopsids (to date, all centrosaurines) in North America, with a number of specimens recovered from throughout a unit that spans between 81 and 77 Ma. Only a single specimen has been formally named, Diabloceratops eatoni, from the lower middle member of the formation. Machairoceratops cronusi gen. et sp. nov., a new centrosaurine ceratopsid from the upper member of the Wahweap Formation, is here described based on cranial material representing a single individual recovered from a calcareous mudstone. The specimen consists of two curved and elongate orbital horncores, a left jugal, a nearly complete, slightly deformed braincase, the left squamosal, and a mostly complete parietal ornamented by posteriorly projected, anterodorsally curved, elongate spikes on either side of a midline embayment. The fan-shaped, stepped-squamosal is diagnostic of Centrosaurinae, how...

ABSTRACT—The theropod genus and species Ornithomimus velox was erected based on a partial hind limb recovered from the late Maastrichtian Denver Formation. A partial manus, which likely belonged to the same individual, was also recovered and described in the same paper. Ornithomimus edmontonicus is the only other valid species currently recognized in the genus. The validity of Ornithomimus velox has been questioned due to its fragmentary nature and because the diagnostic features identified when the species was erected are now considered characteristic for the family. The pes and manus of Ornithomimus velox were never fully prepared. In the original description, reconstructed metatarsals were figured, but manual phalanges, although preserved, were not described. Here we describe and reevaluate Ornithomimus velox based upon a new preparation of the specimen. Metacarpal proportions are diagnostic for the genus, with metacarpal I longer than metacarpal II, which in turn is longer than metacarpal III. The pes and manus of Ornithomimus velox are smaller than in the type specimen of Ornithomimus edmontonicus. Ornithomimus velox can be distinguished from Ornithomimus edmontonicus based on the robusticity of the pes. Material previously referred to Ornithomimus velox from the Kaiparowits Formation of Utah is older and morphologically distinct and does not represent the same species. The morphological disparity and temporal separation observed in specimens referred to Ornithomimus edmontonicus suggest that it may represent a species complex. The redescription and diagnosis of Ornithomimus velox provides a new framework to investigate ornithomimid systematics.

Fossil caddisfly (Insecta: Trichoptera) larval cases are preserved in some Eocene Green River Formation tufa, and well organized arrays of these calcified larval cases have been misidentified as “Oocardium tufa”. The arrays of caddisfly larval cases occur as superimposed layers of vertically oriented cases. The cases are parallel to each other, closely packed, equal in size, and are oriented perpendicular to the bedding planes of the tufa. In thin section, the cases are composed of detrital carbonate particles, ooids and quartz grains arranged in a single layer along the walls of the cases. The size and arrangement of the particles in the walls of the fossil caddisfly larval cases compares favorably with modern caddisfly larval cases. Correct identification of the origin of this unique tufa fabric enables us to better understand the important role of metazoans (Trichopteran larvae) in some Eocene Lake Gosiute paleoenvironments. Caddisfly larvae played direct and indirect roles in the deposition and erosion of tufa in Lake Gosiute during the deposition of the Laney Member of the Green River Formation.

... LITERATURE CITED. Brochu, CA 2003. Osteology of Tyrannosaurus rex: insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. ... CrossRef. Cifelli, RL, RL Nydam, JG Eaton, JD Gardner, and JI Kirkland. 1999. ...

During much of the Late Cretaceous, a shallow, epeiric sea divided North America into eastern and western landmasses. The western landmass, known as Laramidia, although diminutive in size, witnessed a major evolutionary radiation of dinosaurs. Other than hadrosaurs (duck-billed dinosaurs), the most common dinosaurs were ceratopsids (large-bodied horned dinosaurs), currently known only from Laramidia and Asia. Remarkably, previous studies have postulated the occurrence of latitudinally arrayed dinosaur "provinces," or "biomes," on Laramidia. Yet this hypothesis has been challenged on multiple fronts and has remained poorly tested.

Although upper Campanian dinosaur assemblages are well-known from Alberta, Montana, southern Utah, and New Mexico, specimens from Wyoming and central and eastern Utah are very rare. This area constitutes a biogeographic break between northern and southern biogeographic provinces, so any specimens from this region are critical to understanding the origin, evolution, and limits of upper Campanian biogeographic zones on the west margin of the Western Interior Seaway. We report the discovery of a theropod dinosaur partial hindlimb from the Book Cliffs area northeast of Green River, Utah. The specimen was recovered from the Palisade coal zone in the Neslen Formation (Mesaverde Group), which is dated to the mid-Campanian based on ammonite biostratigraphy and radioisotopic age constraints. The specimen, comprising a partial fibula, the distal half of metatarsal II, a complete metatarsal IV, and a partial metatarsal V, can be assigned to Tyrannosauridae based on a number of synapomorphies, including a bipartite iliofibularis tubercle on the fibula and a teardrop shaped articular surface for metatarsal III on the medial surface of the distal portion of metatarsal IV. This is the first unambiguous tyrannosaurid dinosaur reported from the Mesaverde Group and represents an important biogeographic record situated between northern and southern upper Campanian vertebrate assemblages. Specifically, we identify morphological evidence on the pes that separates northern (Montana and Alberta) and southern (southern Utah and New Mexico) tyrannosaurid dinosaurs, and suggests that the Book Cliffs specimen belongs to the northern group. This implies that either the biogeographic boundary between the northern and southern Campanian assemblages lies somewhere between central and southern Utah or that the Book Cliffs taxon represents a northern emigrant in the southern assemblage.

In 2001, the Utah Museum of Natural History (UMNH) of the University of Utah established a collaborative agreement with Grand Staircase-Escalante National Monument, initiating the Kaiparowits Basin Project. The primary goals of this multidisciplinary effort have been to survey and collect remains of dinosaurs and other vertebrates from the Upper Cretaceous Wahweap and Kaiparowits formations. The ultimate objective is to reconstruct the changing nature of these Late Cretaceous ecosystems and place them into context with other coeval ...

[Extract] A collaborative palaeontologicsl survey conducted by the Utah Museum of Natural History and the Bureau of Land Management in the Upper Cretaceous Kaiparowits Formation, in Grand Staircase-Escalante National Monument, southern Utah, has yielded remains of at least three new ceratopsid dinosaur taxa from multiple localities. Significant ceratopsid specimens excavated and collected from these localities provide the basis of a taphonomic study of ceratopsian deposition in the Kaiparowits Formation. Most ...

Previous biogeographic studies of late Cretaceous (late Campanian) vertebrate faunas in the Western Interior Basin (WIB) of North America have suggested the presence of faunal and floral provincialism, characterized by distinct northern and southern 'biomes.'However, the “provincialism hypothesis” has been questioned based largely on the contention that the investigated faunas were recovered from a series of diachronous, time-transgressive deposits, and are therefore non-correlative. Extensive work in several fossiliferous units of ...

The fossil record of centrosaurine ceratopsids is largely restricted to the northern region of western North America (Alberta, Montana and Alaska). Exceptions consist of single taxa from Utah ( Diabloceratops ) and China ( Sinoceratops ), plus otherwise fragmentary remains from the southern Western Interior of North America. Here, we describe a remarkable new taxon, Nasutoceratops titusi n. gen. et sp., from the late Campanian Kaiparowits Formation of Utah, represented by multiple specimens, including a nearly complete skull and partial postcranial skeleton. Autapomorphies include an enlarged narial region, pneumatic nasal ornamentation, abbreviated snout and elongate, rostrolaterally directed supraorbital horncores. The subrectangular parietosquamosal frill is relatively unadorned and broadest in the mid-region. A phylogenetic analysis indicates that Nasutoceratops is the sister taxon to Avaceratops , and that a previously unknown subclade of centrosaurines branched off early in th...

The Late Cretaceous (,95–66 million years ago) western North American landmass of Laramidia displayed heightened non-marine vertebrate diversity and intracontinental regionalism relative to other latest Cretaceous Laurasian ecosystems. Processes generating these patterns during this interval remain poorly understood despite their presumed role in the diversification of many clades. Tyrannosauridae, a clade of large-bodied theropod dinosaurs restricted to the Late Cretaceous of Laramidia and Asia, represents an ideal group for investigating Laramidian patterns of evolution. We use new tyrannosaurid discoveries from Utah—including a new taxon which represents the geologically oldest member of the clade—to investigate the evolution and biogeography of Tyrannosauridae. These data suggest a Laramidian origin for Tyrannosauridae, and implicate sea-level related controls in the isolation, diversification, and dispersal of this and many other Late Cretaceous vertebrate clades.

—While many studies have described the paleontology and paleoecology of the Green River Formation in Fossil Basin, few have focused on the latter stages of Fossil Lake's history. The upper portion of the Fossil Butte Member and the Angelo Member of the Green River Formation represent the latter stages of Fossil Lake. Dolomite and evaporites characterize the upper unit. Desiccation cracks, flat pebble conglomerates and sediments disrupted by evaporites are common, suggesting an arid depositional environment. Sharp bottom contacts of lithologic beds suggest rapid changes in lake levels. The flora includes prokaryotic algae, stromatolites, algal tufa and vascular plants. Angiosperms are relatively scarce, and the palynoflora is dominated by gymnosperms. The fauna and other organisms include bacteria, protists, invertebrates, fish, birds and reptiles. Fish communities of the upper unit are restricted to facies deposited under relatively fresh conditions, and include Priscacara liops, P. hypsacantha, Lepisosteus, Knightia, Diplomystus and Asineops squamifrons. The shorebird Presbyornis is present in marginal facies. The latter stages of Fossil Lake exhibit different communities than those present during most of Fossil Lake's history. Stromatolites and tufa become common. The tiny fish Priscacara hypsacantha dominates fish populations, while the major predator was Lepisosteus. These fish adjusted to increasing alkalinity and salinity by retreating to nearshore freshwater environments. Cooler gymnosperm-dominated floras replaced subtropical angiosperm floras. The flora and faunas of the upper unit represent a unique paleocommunity that represents a response to the changing conditions of upper unit time. These organisms dealt with increasing alkalinity, salinity and fluctuating lake levels.

____________________ ABSTRACT—The Caddisfly (Trichoptera) larval cases from two sites in the Green River Formation of Eocene Fossil Basin are predominantly preserved as aggregates of calcareous tubes. The cases are tube shaped, slightly curved and generally lack sand grains or other particles in their case wall structure. Rare caddisfly larval cases from both sites show carbonate particles incorporated into the case structure. We believe that these caddisfly larval cases were constructed primarily of silk. The caddisfly larval cases are associated with lake-margin tufa, stromatolites and tufa-encrusted logs. This association illustrates the influence of metazoans in shaping the internal fabric of these Eocene lacustrine tufas. ____________________