Poposaurus

About: Poposaurus is a research topic. Over the lifetime, 13 publications have been published within this topic receiving 751 citations. The topic is also known as: Lythrosuchus.

Postosuchus, a New Thecodontian Reptile from the Triassic of Texas and the Origin of Tyrannosaurs

Abstract: Postosuchus kirkpatricki (n.g., n.sp.) is a large, gracile, carnivorous thecodontian from the late Triassic Dockum Group of Texas. The species is characterized by its erect and facultative bipedal gait, highly advanced pelvis with slightly open acetabulum and footed pubis. The teeth are large, highly serrated, deeply set in sockets, and show a wave-like replacement pattern. Some flexibility in the palate and the lower jaw permitted the animal to swallow large chunks of flesh. Postosuchus was the arch predator of its time, and lived in the interfluves or upland regions along with aetosaurs, coelurosaurs, and ictidosaurs. The quarry's thanatocoenose probably reflects autochthonous burials of a Dockum community, perhaps in consequence of a catastrophic event such as a flash flood. Although Postosuchus exhibits many carnosaurian traits, its ankle joint is of \`crocodile-normal' pattern, which suggests its pseudosuchian affinity. All Triassic reptiles previously thought to be carnosaurs are considered herein as advanced thecodontians; true carnosaurs probably appeared in post-Triassic time. Postosuchus is grouped with Poposaurus, Teratosaurus, Arizonasaurus and the unnamed \`Warwick archosaur' in the family Poposauridae. The Poposauridae and Rauisuchidae are placed in the infraorder Rauisuchia. Tyrannosaurs probably evolved from poposaurids, as indicated by the correlation between skull, pelvis and ankle structure.

The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa

Abstract: Effigia okeeffeae is named based on a well-preserved nearly complete skeleton from the Upper Triassic (?Rhaetian) “siltstone member” at Ghost Ranch, northern New Mexico. The skull is described and compared to other suchian and basal archosaurs. The maxilla and premaxilla are edentulous, and a rhamphotheca was possibly present in life. Effigia conclusively indicates that the skull of Shuvosaurus and the postcrania of “Chatterjeea” belong to the same taxon. Furthermore, the close relationship between Shuvosaurus and Effigia indicates that both taxa are nested within the suchian clade and not within Ornithomimisauria. However, the similarity in features in the skull and postcrania of Effigia and ornithomimids suggests extreme convergence occurred between the two clades. A clade containing Arizonasaurus, Bromsgroveia, Poposaurus, Sillosuchus, Shuvosaurus, and Effigia is suggested based solely on shared derived character states. Additionally, a clade (Clade Y) containing Sillosuchus, Shuvosaurus, and ...

Osteology of the Middle Triassic pseudosuchian archosaur Arizonasaurus babbitti

Abstract: Arizonasaurus babbitti is rediagnosed from a well-preserved partial skeleton from the early Middle Triassic Moenkopi Formation of northern Arizona. The skull, excluding the braincase, is described and compared to other “rauisuchians” and basal archosaurs. Two possible autapomorphies include a deep fossa hidden from lateral and medial views on the posteroventral edge of the ascending process of the maxilla and a tongue (pubic peduncle of the ilium) and groove (proximal portion of the pubis) articulation between the pubis and the ilium. The postcrania is described in detail. Tall neural spines form a sail that is similar to those of other basal archosaurs with unknown affinities (Ctenosauriscus, Lotosaurus, Bromsgroveia, “Hypselorhachis”). Additional characters in the pelvic girdle in Arizonasaurus unite this taxon with Ctenosauriscus, Lotosaurus, Bromsgroveia, and Hypselorhachus to form a group, the ctenosauriscids. Pelvic characters of the ctenosauriscids are also found in Poposaurus and “Chatterjeea”, su...

The Bipedal Stem Crocodilian Poposaurus gracilis: Inferring Function in Fossils and Innovation in Archosaur Locomotion

Abstract: We introduce a spectacular new specimen of a Late Triassic stem crocodilian identified as Poposaurus gracilis. It is part of a poorly known group, Poposauroidea, that, because of its striking similarities with contemporaneous stem avians (“dinosaurs”), has long puzzled archosaur paleontologists. Observed vertebrate locomotor behaviors, together with exceptional preservation of distinctive anatomical clues in this fossil, enable us to examine locomotor evolution in light of new advances in phylogenetic relationships among Triassic archosaurs. Because this stem crocodilian is unambiguously an archosaur, a diapsid, a tetrapod and a choanate sarcopterygian, we can safely infer major components of its locomotor behavior. These inferences, together with form-function constraints, suggest that P. gracilis was a fleet-footed, obligately erect-postured, striding biped. That behavior seems to have been superimposed on the ancestral archosaur's innovative locomotor repertoire, which includes the capacity to...

A revision ofPoposaurus gracilis (Archosauria: Suchia) based on two new specimens from the Late Triassic of the southwestern U.S.A.

Abstract: Two associated partial skeletons, one from the McCarty ranch (MOTTU site 0690) near Kalgary, Texas, Tecovas Formation, and the other from the Petrified Forest Member of the Chinle Formation, outside the Petrified Forest, Arizona, represent the most complete specimens ofPoposaurus gracilis found to date, and increase our understanding of the osteology of this rare pseudosuchian archosaur. The cervical centrum of TTUP-10419 possesses an accessory dorsal parapophyseal rib facet, as in “Lythrosuchus”. The ilia of these new fossils are the first ofPoposaurus to preserve the complete preacetabular blade, which is long and “blade-like” rather than “paddle-shaped” as previously thought. These specimens also confirm that isolated elements previously referred toPoposaurus (fused sacral vertebrae, the pubes and the ischia), but not present in the holotype indeed belong to that taxon. The morphology of the cervical centrum and the preacetabular blade of the ilium are identical to the much larger type of“Lythrosuchus” langstoni, suggesting that “Lythrosuchus” is a junior synonym ofPoposaurus. However, we retain the speciesPoposaurus langstoni nov. comb. on the basis of larger size, absence of a distinct ridge on the lateral surface of the ilium, and the lack of a pit on the proximal end of the ischium. A phylogenetic analysis suggests a monophyletic Poposauroidea and a paraphyletic “Rauisuchia”.