Scott D. Sampson

Denver Museum of Nature and Science

The skull and associated postcrania of Nasutoceratops titusi, a basal centrosaurine ceratopsid from the Upper Cretaceous (Campanian) Kaiparowits Formation of Grand Staircase–Escalante National Monument, southern Utah, are herein described. Autapomorphies of this taxon include: an ectonaris that comprises 75% of preorbital skull length; pneumatic na...

Fossil vertebrates from the Gokwe Formation (Fm) of central Zimbabwe have been known for over 50 years, yet remain poorly understood due in part to their poor preservation and the uncertainty surrounding their age, previously constrained to Upper Jurassic-Cretaceous. Collections from the Gokwe Fm include a diverse array of vertebrate fossils that b...

The Wahweap Formation preserves the most di-verse middle Campanian terrestrial fauna in North America, based largely on information gained by the study of micro-vertebrate fossils collected by wet screen washing. These studies have documented a minimum of fi ve freshwater shark species, three freshwater ray species, eight bony fi sh species, 11 amp...

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 t...

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 remarka...

Tetanuran theropods represent the majority of Mesozoic predatory dinosaur diversity and the lineage leading to extant Aves. Thus their history is relevant to understanding the evolution of dinosaur diversity, Mesozoic terrestrial ecosystems, and modern birds. Previously, the fragmentary and poorly sampled fossil record of basal (non-coelurosaur) te...

The American West once harbored multiple communities of dinosaurs simultaneously—a revelation that has scientists scrambling to understand how the land could have supported so many behemoths

Extended results of phylogenetic analysis, consisting of: 1) character taxa; and 2) taxon-character matrix. (0.09 MB DOC)

Phylogenetic relationships of Utahceratops gettyi and Kosmoceratops richardsoni within Ceratopsidae. Strict consensus of 3 most parsimonious trees (tree length = 263; CI = 0.6692; CI excluding uninformative characters = 0.6602; HI = 0.3308; HI excluding uninformative characters = 0.3398; RI = 0.7904; RC = 0.5289). Bootstrap values greater than 50%...

Background: 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 (la...

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 contentio...

The purpose of this application, under Articles 75.5 and 75.6 of the Code, is to replace the existing, non-diagnostic holotype of Megalosaurus crenatissimus Depéret, 1896 (currently Majungasaurus crenatissimus) by a neotype. The designation of a neotype is necessary to conserve the prevailing usage and concept of the species. 1. Charles Depéret (18...

The purpose of this application, under Articles 75.5 and 75.6 of the Code, is to replace the existing, non-diagnostic holotype of Megalosaurus crenatissimus Depéret, 1896 (currently Majungasaurus crenatissimus) by a neotype. The designation of a neotype is necessary to conserve the prevailing usage and concept of the species.

A new lambeosaurine hadrosaurid, Velafrons coahuilensis, is described as the first lambeosaurine from the Cerro del Pueblo Formation of Coahuila, Mexico, and the first lambeosaurine genus to be named from North America in more than 70 years. Although the holotype specimen is a juvenile individual—as evidenced by its incomplete crest development and...

We report the occurrence of a furcula (fused clavicles) in both species of the Early Jurassic coelophysid theropod dinosaur Syntarsus (Coelophysidae sensu Holtz, 1994; Coelo-physis and Syntarsus and all descendants of their most recent common ancestor). The furcula is a median pectoral element formed by ontogenetic fusion of the left and right clav...

The Mahajanga Basin Project, initiated in 1993 and centered in Upper Cretaceous strata of northwestern Madagascar, has resulted in the discovery of some of the most complete, well-preserved, and significant specimens of Late Cretaceous vertebrate animals from the Southern Hemisphere and indeed the world. Among the most important finds are various s...

SYNOPSIS Recent discoveries and analyses have drawn increased attention to Ceratosauria, a taxo-nomically and morphologically diverse group of basal theropods. By the time of its first appearance in the Late Jurassic, the group was probably globally distributed. This pattern eventually gave way to a primarily Gondwanan distribution by the Late Cret...

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A new species of the hadrosaurine hadrosaurid Gryposaurus was discovered in the late Campanian Kaiparowits Formation of southern Utah. Gryposaurus monumentensis, sp. nov. is distinguished from other Gryposaurus species by possessing a more robust skull, enlarged clover-shaped prongs on the predentary oral margin, an anteroposteriorly narrow infrate...

We review the historical sequence of discoveries of Majungasaurus crenatissimus, an abelisaurid theropod from the Upper Cretaceous (Maastrichtian) Maevarano Formation, Mahajanga Basin, northwestern Madagascar. For almost a century, beginning in 1895, periodic expeditions conducted by French, Japanese, and Malagasy teams yielded fragmentary and isol...

Recent fieldwork in the Upper Cretaceous (Maastrichtian) Maevarano Formation, northwest Madagascar, has yielded important new skull material of the abelisaurid theropod, Majungasaurus crenatissimus. One of these specimens in particular—a virtually complete, disarticulated, and well preserved skull—greatly elucidates the craniofacial osteology of ab...

Recent fieldwork in the Upper Cretaceous (Maastrichtian) Maevarano Formation, northwest Madagascar, has yielded important new skull material of the abelisaurid theropod, Majungasaurus crenatissimus. One of these specimens in particular - a virtually complete, disarticulated, and well preserved skull - greatly elucidates the craniofacial osteology o...

The Kaiparowits Basin Project was initiated in 2000 in order to explore Upper Cretaceous deposits preserved within Grand Staircase-Escalante National Monument. In particular, emphasis has been placed on excavation and study of macrovertebrates from two Campanian-aged units—the Kaiparowits and Wahweap formations. Results to date have been abundant a...

The Kaiparowits Basin Project—a joint collaboration between the Utah Museum of Natural History and the University of Utah—has made significant additions to the previously recognized theropod dinosaur fauna of the late Campanian Kaiparowits Formation of southern Utah. Results of this project include: the discovery of Hagryphus giganteus, the first d...

Recent field expeditions to Upper Cretaceous deposits within Grand Staircase-Escalante National Monu-ment, southern Utah, have revealed a diverse dinosaurian fauna that includes a previously unknown oviraptorosaur theropod. Represented by a single partial specimen consisting of manal and pedal elements, this new taxon, Hagryphus giganteus, gen. et....

Here we redescribe the holotype and only specimen of Segisaurus halli, a small Early Jurassic dinosaur and the only theropod known from the Navajo Sandstone. Our study highlights several important and newly recognized features that clarify the relationships of this taxon. Segisaurus is clearly a primitive theropod, although it does possess a tetanu...

Therizinosauroids are an enigmatic group of dinosaurs known mostly from the Cretaceous period of Asia, whose derived members are characterized by elongate necks, laterally expanded pelves, small, leaf-shaped teeth, edentulous rostra and mandibular symphyses that probably bore keratinized beaks. Although more than a dozen therizinosauroid taxa are k...

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The Kaiparowits Basin, located mostly within Grand Staircase–Escalante National Monument, preserves an outstanding record of Late Cretaceous sedimentation in a foreland basin setting. Hosted in these rocks is one of the most continuous and complete records of this period's ecosystems known from any one geographic area in the world. Recent work in t...

This chapter focuses on the ceraptopsids, a monophyletic group of large-bodied (4–8 m long), quadrupedal, and herbivorous dinosaurs. Ceraptosids have elaborate horns and frills and complex dental batteries. Fossil remains have been confirmed only in the United States, Canada, and Mexico. Ceratopsidae consists of two well-defined clades: Centrosauri...

Project WEST (Water, the Environment, Science, and Teaching) is a graduate student fellowship program funded by a GK-12 grant from the National Science Foundation. WEST links the University of Utah, the Utah Museum of Natural History, and the Salt Lake City school district in enhancing inquiry based science teaching in grades 4, 8, and 9 and the in...

We review the available materials of Early Jurassic European theropods and confirm several as belonging to the clade Coelophysoidea. These include the holotypic partial skeleton of Liliensternus airelensis (France), fragmentary remains referred to as Sarcosaurus woodi and Sarcosaurus andrewsi (England), and a distal tibia (Scotland). Although incom...

Principal and supplementary reference sections provide data that clarify the stratigraphic relationships and depositional history of the Cerro del Pueblo Formation (CdP) - an important unit in Late Cretaceous paleobiogeographic studies in northeastern Mexico and the Western Interior of North America. At Saltillo, the CdP is 162 m thick, much thinne...

We describe the osteology of the new small theropod dinosaur Masiakasaurus knopfleri, from the Late Cretaceous Maevarano Formation of northwestern Madagascar. Approximately 40% of the skeleton is known, including parts of the jaws, axial column, forelimb, pelvic girdle, and hind limb. The jaws of Masiakasaurus are remarkably derived, bearing a hete...

We describe the osteology of the new small theropod dinosaur Masiakasaurus knopfleri, from the Late Cretaceous Maevarano Formation of northwestern Madagascar. Approximately 40% of the skeleton is known, including parts of the jaws, axial column, forelimb, pelvic girdle, and hind limb. The jaws of Masiakasaurus are remarkably derived, bearing a hete...

We describe the osteology of the new small theropod dinosaur Masiakasaurus knopfleri, from the Late Cretaceous Maevarano Formation of northwestern Madagascar. Approximately 40% of the skeleton is known, including parts of the jaws, axial column, forelimb, pelvic girdle, and hind limb. The jaws of Masiakasaurus are remarkably derived, bearing a hete...

Here we report the discovery of a small-bodied (approximately 1.8 m) predatory dinosaur from the Late Cretaceous (Maastrichtian) of Madagascar. Masiakasaurus knopfleri, gen. et sp. nov., represented by several skull elements and much of the postcranial skeleton, is unique in being the only known theropod with a highly procumbent and distinctly hete...

We report the well preserved skeleton of a small theropod dinosaur, Nqwebasaurus thwazi, gen. et sp. nov., from the Lower Cretaceous Kirkwood Formation of South Africa. Nqwebasaurus has an elongate three-digit manus with a partially opposable first digit, a long and slender pes with a highly reduced metatarsal IV, and preserves gastroliths (stomach...

The Cleveland-Lloyd Dinosaur Quarry (CLDQ) of central Utah contains an extensive sample of Allosaurus fragilis, the largest known for any large theropod taxon. This collection, along with isolated articulated specimens, forms the material basis of a study of ontogenetic change in the hindlimb of this Late Jurassic theropod dinosaur. Previous resear...

The trunk-like proboscis of tapirs provides a prime case study in the evolution of anatomical novelty. Morphological study of this unique structure was undertaken employing several specimens and a combination of analytical techniques: gross anatomical dissection, radiographic imaging and histological sectioning. Evolution of the proboscis of tapirs...

A rich, newly discovered assemblage of exquisitely preserved vertebrate fossils from the Late Cretaceous of Madagascar provides an unparalleled opportunity to investigate the paleobiogeography of Gondwanan landmasses. Most current plate tectonic models depict widespread fragmentation of Gondwana prior to the Late Cretaceous. The discovery of mammal...

A growing body of research posits a central role for mating signals in speciation and the reproductive isolation of species, yet there has been relatively little consideration of mating signal evolution within macroevolutionary theory. Factors that influence the divergence of fertilization systems generally, and mating signals specifically, may inc...

In 1896 Charles Depéret described a fauna of dinosaurs from the Upper Cretaceous (?Campanian) Maevarano Formation from the Mahajanga Basin of northwest Madagascar. Among the dinosaurs was a titanosaurid sauropod that he named Titanosaurus madagascariensis. He attributed to the titanosaurid a large, thick circular osteoderm. His referral of an osteo...

Recent discoveries of fossil vertebrates from the Late Cretaceous of Madagascar include several specimens of a large theropod dinosaur. One specimen includes a nearly complete and exquisitely preserved skull with thickened pneumatic nasals, a median frontal horn, and a dorsal projection on the parietals. The new materials are assigned to the enigma...

Genus Correction The name Rahona, which we recently proposed as a genus name for a basal avian from the Late Cretaceous of Madagascar (Reports, 20 Mar., p. 1915), is already occupied by the lymantriid lepidopteran Rahona Griveaud, (1). We therefore propose the replacement name Rahonavis for this genus, whose type species is Rahonavis ostromi.

A partial skeleton of a primitive bird, Rahona ostromi, gen. et sp. nov., has been discovered from the Late Cretaceous of Madagascar. This specimen, although exhibiting avian features such as a reversed hallux and ulnar papillae, retains characteristics that indicate a theropod ancestry, including a pubic foot and hyposphene-hypantra vertebral arti...

Centrosaurine ceratopsians are characterized by well developed nasal horncores or bosses, relatively abbreviated supraorbital horncores or bosses, and adorned parietosquamosal frills. Recent study of several paucispecific (low diversity) bonebed assemblages in Alberta and Montana has contributed greatly to our understanding of ontogenetic and taxon...

Our knowledge of Mesozoic birds from Gondwana has been derived almost entirely from South America, Australia, and the Antarctic Peninsula. Several representing at least three distinct taxa of birds, were recently recovered from the Campanian Maevarano Fm., Mahajanga Basin, northwestern Madagascar. This avifauna provides the first pre Late-Holocene...

WE report the discovery of two exquisitely preserved specimens of a new, very primitive bird from the Late Cretaceous period of Madagascar. The new taxon, Vorona berivotrensis, is provisionally placed phylogenetically in an unresolved trichotomy with Enantiornithes and a clade consisting of Patagopteryx and Ornithurae. These specimens are the first...

Two new ceratopsid dinosaurs, Einiosaurus procurvicornis and Achelousaurus horneri, are described from the Two Medicine Formation (Upper Cretaceous) of Montana. E. procurvicornis is known from three skulls and numerous cranial and postcranial elements from two bonebed assemblages. A. horneri is based on three skulls, one with associated postcranial...