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We describe the basal sauropodomorph Eoraptor lunensis, based on the nearly complete holotypic skeleton and referred specimens, all of which were discovered in the Cancha de Bochas Member of the Ischigualasto Formation in northwestern Argentina. The lightly built skull has a slightly enlarged external naris and a spacious antorbital fossa with a prominent, everted dorsal margin and internal wall lacking any pneumatic extensions into surrounding bones. The tall quadrate is lapped along its anterior margin by the long, slender ventral process of the squamosal, and the lower jaw has a mid-mandibular joint between a tongue-shaped splenial process and a trough in the angular. All but the posterior-most maxillary and dentary crowns have a basal constriction, and the marginal denticles are larger and oriented more vertically than in typical theropod serrations. Rows of rudimentary palatal teeth are present on the pterygoid. Vertebral centra are hollow, although not demonstrably pneumatized, and all long...

The systematics and taxonomy of the large allosauroid Carcharodontosaurus are reviewed and a new species of this theropod is described from the Late Cretaceous (Cenomanian) Echkar Formation of Niger, which is roughly coeval with Cenomanian beds elsewhere in northern Africa. The type species, C. saharicus, was based originally on a pair of isolated teeth from Algeria, to which was referred a partial skull and skeleton from Egypt. All of this material was either lost or destroyed more than 50 years ago. Thus, a neotype is designated for C. saharicus, a well-preserved cranium from the Kem Kem beds in Morocco. Newly discovered material from Niger is distinct from that of C. saharicus, justifying the erection of a distinct southern species. C. iguidensis, n. sp. is represented by cranial (maxilla, braincase, dentary, lacrimal, teeth) and postcranial (vertebrae) remains and grew to the same large body size as C. saharicus. The skull displays several autapomorphies, including a laterally reduced externa...

(2003). A new notosuchian from the Early Cretaceous of Niger. Journal of Vertebrate Paleontology: Vol. 23, No. 2, pp. 477-482.

(2000). Forebrain enlargement among nonavian theropod dinosaurs. Journal of Vertebrate Paleontology: Vol. 20, No. 3, pp. 615-618.

We review the morphology and systematics of Lagosuchus from the Middle Triassic Los Chanares Formation. Two species have been named, Lagosuchus talampayensis and L. lilloensis. The holotype of Lagosuchus talampayensis is a fragmentary skeleton that does not exhibit any autapomorphies to distinguish it from contemporary dinosauromorphs, and the genus and species are regarded as nomina dubia. In contrast, the holotype of Lagosuchus lilloensis is a well-preserved skeleton that exhibits several distinctive features, allowing reference of additional specimens. We, therefore, designate a new genus, Marasuchus, for the species “Lagosuchus” lilloensis. Several synapomorphies unite Marasuchus and dinosaurs (as Dinosauriformes) to the exclusion of the contemporary dinosauromorph Lagerpeton and pterosaurs. These include an antitrochanter on the posterior wall of the acetabulum, an anterior (lesser) trochanter developed as a trochanteric shelf, and a posterior flange on the distal end of the tibia. These din...

We describe the skull and neck of Herrerasaurus ischigualastensis from specimens discovered recently in the Upper Triassic Ischigualasto Formation of northwestern Argentina. The skull has a rectangular profile and a transversely narrow snout. Marked supratemporal depressions for jaw adductor musculature on the skull roof and a well-developed, sliding intra-mandibular joint suggest that Herrerasaurus ischigualastensis was an active predator. The neck is relatively slender with prominent epipophyses on all of the cervical vertebrae. Diagnostic features of the species include the semicircular shape of the antorbital fossa and the long, slender posterodorsal process of the dentary. Other features of the skull, such as the loss of the postfrontal and small post-temporal opening, constitute dinosaurian synapomorphies. These synapomorphies, however, remain equivocal at the level of Dinosauria because they cannot be evaluated in immediate dinosaurian outgroups for which cranial information is lacking. Co...

We describe the holotype and referred material of the unusual Middle Triassic dinosaur precursor, Lagerpeton chanarensis. The autapomorphies of Lagerpeton chanarensis include the convex and fluted puboischial flange, hook-shaped femoral head, elongate femoral fourth trochanter, fused astragalocalcaneum, tall posterior ascending process on the astragalus, and functionally didactyl pes. Among ornithodirans, Lagerpeton chanarensis is more closely related to dinosaurs than are pterosaurs. We list tarsal and pedal synapomorphies shared by Lagerpeton chanarensis and other dinosauromorphs that are absent in pterosaurs and crurotarsal archosaurs. These include an increase in the relative size of the central metatarsals and subparallel orientation of pedal digit V. There is no evidence that Lagerpeton and other small-bodied dinosauromorphs in the Los Chanares fauna, namely “Lagosuchus” lilloensis, comprise a monophyletic group. The digitigrade pes and the elongate and erect hind-limbs of basal pterosaurs ...

New specimens of Herrerasaurus ischigualastensis shed light on the structure and function of the pectoral girdle and forelimb in early theropod dinosaurs. As in tetanurian theropods, the scapulocor...

The recent discovery of a nearly complete ceratopsid skull in the Aguja Formation of southwest Texas supports previous conclusions that the Aguja ceratopsid represents a distinct species, Chasmosaurus mariscalensis. The diagnostic features of C. mariscalensis include an extensive anteromedian projection of the nasal between the premaxillae, erect supraorbital horns, and laterally rounded squamosal. Nine cranial features that vary among Chasmosaurus species, Pentaceratops sternbergii, and other chasmosaurines are analyzed. Chasmosaurus mariscalensis appears to be most closely related to northern species of Chasmosaurus (C. belli, C. russelli), which also exhibit a transversely flattened nasal horn and modifications of the anterior margin of the external naris. The genus Chasmosaurus, in turn, appears to be most closely related to the other southern chasmosaurine, Pentaceratops sternbergii. The biogeographic history inferred from these relationships suggests that the biogeographic exchange between ...

We show that Procompsognathus triassicus, long held to be a primitive theropod, is actually a paleontological chimera composed of the postcranial skeleton of a Segisaurus-like ceratosaur and the skull of a basal crocodylomorph. We dismember the holotype of P. triassicus on convincing evidence—theropod synapomorphies in the postcranium and crocodylomorph synapomorphies in the skull and referred material. We demonstrate, furthermore, that the holotype skull and a referred skull and partial forelimb belong to the contemporary basal crocodylomorph Saltoposuchus connectens. Saltoposuchus connectens, now with a nearly complete skull, carpus, and manus, is compared in detail to other basal crocodylomorphs. Current opinion maintains that S. connectens is the sister-group to all other crocodylomorphs and that other sphenosuchians constitute a paraphyletic assemblage of sister-taxa to Crocodyliformes. This view is overturned by a quantitative cladistic analysis of 20 characters, which suggests that by the ...

The recent discovery of the Middle Jurassic stegosaur, Huayangosaurus taibaii has shed new light on the early phylogeny of Stegosauria. The skull of this taxon is described in detail and compared to those of other thyreophorans. Cranial and postcranial autapomorphies of Huayangosaurus include high premaxillary and maxillary tooth counts (7 and 25–30, respectively), small postorbital horn, intercostal articular flanges, and a carpus composed of a single coossified block. Nineteen synapomorphies unite Huayangosaurus and other stegosaurs and constitute a revised cladistic diagnosis for Stegosauria. Huayangosaurus is the sister-taxon to all other stegosaurs, which have lost premaxillary teeth, reduced the size of the antorbital fossa, increased the length of the prepubic process of the pubis, and lost lateral scute rows along the trunk.

Archosaurs first appeared in the Middle Triassic and within a short interval of time came to dominate all faunas of large vertebrates for the remainder of the Mesozoic. It is widely held that short...

(1999). A rationale for dinosaurian taxonomy. Journal of Vertebrate Paleontology: Vol. 19, No. 4, pp. 788-790.

(2007). The systematic utility of theropod enamel wrinkles. Journal of Vertebrate Paleontology: Vol. 27, No. 4, pp. 1052-1056.

A new psittacosaur species, Psittacosaurus meileyingensis, is based on a well preserved skull with referred cranial and postcranial remains. The skull is tall relative to its length and has a subcircular profile. Distinctive characteristics of the new species include a low horn on the quadratojugal and a prominent ventral flange on the dentary. The discovery of both Psittacosaurus meileyingensis and Psittacosaurus mongoliensis in the same formation strongly suggests their coexistence.