The most commonly cited apomorphy of Archosauriformes is an opening in the snout known as the antorbital cavity. Despite the ubiquity and prominence of the antorbital cavity, its function and importance in craniofacial evolution have been problematic. Discovering the significance of the antorbital cavity is a two step process: first, establishing the function of the bony cavity (that is, its soft-tissue relations), and second, determining the biological role of the enclosed structure. The first step is the most fundamental, and hence is examined at length. Three hypotheses for the function of the antorbital cavity have been advanced, suggesting that it housed (1) a gland, (2) a muscle, or (3) a paranasal air sinus. Thus, resolution is correctly viewed as a “soft-tissue problem,” and is addressed within the context of the extant phylogenetic bracket (EPB) approach for reconstructing the unpreserved features of fossil organisms. The soft-anatomical relations of the antorbital cavity (or any bony st...

The Evolution of the Antorbital Cavity of Archosaurs: A Study in Soft-Tissue Reconstruction in the Fossil Record with an Analysis of the Function of Pneumaticity

Allosaurus Fragilis: a Revised Osteology

A detailed osteological description of Tyrannosaurus rex Osborn, 1905 is presented, based primarily on the most complete specimen yet collected of this taxon (FMNH PR2081, popularly known as “Sue”) but also including observations from other specimens. Skull morphology of FMNH PR2081 is largely congruent with that described for previous specimens, but new details are added. Palatal morphology of FMNH PR2081 differs slightly from that of previously-described specimens—the internal choanae are slightly larger relative to skull size, and the anterior expansion of the fused vomers is elongate. Posteriorly, the vomers pass medially for nearly the entire length of the pterygoids. High-resolution x-ray computed tomographic (CT) analysis of the skull reveals internal details not previously observed. Complex recess systems can be traced in the jugal, lacrymal, ectopterygoid, quadrate, exoccipital, supraoccipital, prootic, and basioccipital. The exoccipital recess was perforated by a small foramen on the po...

Osteology of Tyrannosaurus Rex: Insights from a nearly complete Skeleton and High-Resolution Computed Tomographic Analysis of the Skull

Late Cretaceous (Cenomanian) fossils discovered in the Kem Kem region of Morocco include large predatory dinosaurs that inhabited Africa as it drifted into geographic isolation. One, represented by a skull approximately 1.6 meters in length, is an advanced allosauroid referable to the African genus Carcharodontosaurus. Another, represented by a partial skeleton with slender proportions, is a new basal coelurosaur closely resembling the Egyptian genus Bahariasaurus. Comparisons with Cretaceous theropods from other continents reveal a previously unrecognized global radiation of carcharodontosaurid predators. Substantial geographic differentiation of dinosaurian faunas in response to continental drift appears to have arisen abruptly at the beginning of the Late Cretaceous.

https://science.sciencemag.org/content/sci/272/5264/986.full.pdf

Predatory Dinosaurs from the Sahara and Late Cretaceous Faunal Differentiation

A reevaluation of early amniote phylogeny

696 Introduction -697 Type -699 Paratype -699 Generic diagnosis -699 Description of the skeleton -700 Skull -700 Frontals -701 Parietals -701 Prootic -702 Jugal -702 Lachrymal -702 Postorbital complex -703 Squamosal -703 Basioccipital -----703 Exoccipitals and paroccipitals 703 Supraoccipitals -704 Alisphenoids -----------704 Orbitosphenoids and ethmoids 704 Basisphenoids .-.--------------704 Ectopterygoid ---------------705 Lower jaw -705 Measurements of the skull 705 Vertebral column -706 Cervical vertebrae -706 Measurements of the cervical vertebrae -709 Dorsal vertebrae ---709 Measurements of the dorsal vertebrae -711 Caudal vertebrae 711 Measurements of the caudal vertebrae 714 Discussion of the vertebral spines 714 Chevrons 715 Ribs -716 Gastralia -716 Pectoral girdle -716 Coracoid -716 Pelvic girdle -717 Pubis -717 Ischium 717 Hind limb7J!9 Femur -718 Tibia -718 Fibula -719 Pes -719 Measurements of the hind limb and foot -720 Observations on the taxonomy of Altispinax -721 The relationships of Acrocanthosaurus 722 Conclusions 723 Acknowledgments -724 References 724

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Acrocanthosaurus atokensis, a New Genus and Species of Lower Cretaceous Theropoda from Oklahoma

Total length, snout-vent length, and body mass are tightly correlated with length and other dimensions of the femur in Alligator mississippiensis. American alligator-based equations relating total length and body mass to femoral dimensions predict the sizes of other extant crocodylian species reasonably well, suggesting that alligator-based relationships should also work for extinct crocodylians and their close relatives. Size estimates from different femoral dimensions are most consistent when extinct forms have femora similar in size and shape to those of alligators. For many extinct mesoeucrocodylians, alligator femur-based total length estimates are close to length estimates based on reasonably complete skeletons or estimates made from osteological parameters other than femoral dimensions. However, the total length estimated for Pristichampsus is much larger than the length of the skeleton, indicating a relatively longer femur in this form, perhaps reflecting a more terrestrial lifestyle. In ...

Femoral dimensions and body size of Alligator mississippiensis: estimating the size of extinct mesoeucrocodylians

Numerous remains of the azhdarchid pterosaur Quetzalcoatlus sp., have been recovered over the last twenty years from the Late Cretaceous (Maastrichtian) rocks in Big Bend National Park in Trans-Pecos Texas. Among more than 200 bones found at one locality are four incomplete skulls and mandibles, which provide the most complete information about cranial structures in the Azhdarchidae. What is currently known indicates that the Azhdarchidae is the sister group of the Tapejaridae from Early Cretaceous deposits in northeastern Brazil.

Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from Late Cretaceous sediments of Big Bend National Park, Texas

Scabby Butte, a limited exposure of late Cretaceous sediments in southern Alberta, Canada, is an important source for the large ceratopsian dinosaur Pachyrhinosaurus Sternberg. New cranial material confirms this taxon's place among short-faced ceratopsids, and circumstantial evidence suggests that it possessed a spiked frill reminiscent of Styracosaurus. Postcranial bones associated with Pachyrhinosaurus skulls in a bonebed deposit probably belong to the genus and indicate a massive body approaching Triceratops dimensions. Another ceratopsian, Anchiceratops, is sparsely represented.All classes of gnathostomes, except birds, are represented by fragmentary material at Scabby Butte. Of 21 lower vertebrate taxa, fourteen are new to the St. Mary River Formation (Squatirhina, Squatina, Amia, Belonostomus, Paralbula, Platacodon, Opisthotriton, Boremys, Plioplatecarpus, a tyrannosaur, a coelurosaur, an ornithomimid, Troodon, Edmontosaurus, Edmontonia).

The Ceratopsian Dinosaurs and Associated Lower Vertebrates from the St. Mary River Formation (Maestrichtian) at Scabby Butte, Southern Alberta

Aerosaurus wellesi n. sp. is based upon two nearly complete articulated skeletons from the Lower Permian deposits near Arroyo del Agua, New Mexico. Study of these superbly preserved specimens indicates that the genus Aerosaurus is distinguishable from most other pelycosaurs, including Varanops and Varanodon, in having fewer maxillary and dentary teeth, all of which are more laterally compressed and more strongly recurved. The parasphenoid is uniquely expanded laterally and posteriorly, and bears rows of teeth on ridges. Aerosaurus also differs from all other pelycosaurs in which the braincase is adequately known in the formation of the dorsum sellae mainly from the basisphenoid. Aerosaurus was probably an aggressive predator of lizard-like habitus, with an unusually long tail for a pelycosaur. Aerosaurus, Varanops, and Varanodon are the only pelycosaurs that can be included in the family Varanopseidae with certainty; however, Basicranodon may also be a varanopseid. The possibility that the allege...

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Wann Langston

Papers

Acrocanthosaurus atokensis, a New Genus and Species of Lower Cretaceous Theropoda from Oklahoma

Femoral dimensions and body size of Alligator mississippiensis: estimating the size of extinct mesoeucrocodylians

Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from Late Cretaceous sediments of Big Bend National Park, Texas

The Ceratopsian Dinosaurs and Associated Lower Vertebrates from the St. Mary River Formation (Maestrichtian) at Scabby Butte, Southern Alberta

Aerosaurus wellesi, new species, a varanopseid mammal-like reptile (Synapsida : Pelycosauria) from the Lower Permian of New Mexico