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

@inproceedings{Gauthier2011TheBS,
  title={The Bipedal Stem Crocodilian Poposaurus gracilis: Inferring Function in Fossils and Innovation in Archosaur Locomotion},
  author={Jacques A. Gauthier and Sterling J. Nesbitt and Emma R. Schachner and Gabriel S Bever and Walter G. Joyce},
  year={2011}
}
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… 

Pedal Proportions of Poposaurus gracilis: Convergence and Divergence in the Feet of Archosaurs

A comparison of phalangeal, digital, and metatarsal proportions of Poposaurus with those of extinct and extant crocodile‐line archosaurs, obligate or facultatively bipedal non‐avian dinosaurs, and ground birds of several clades shows numerous instances of convergence in pedal morphology among disparate archosaurian clades.

Osteology of the Late Triassic Bipedal Archosaur Poposaurus gracilis (Archosauria: Pseudosuchia) from Western North America

The osteology of this specimen is described in detail and multiple skeletal adaptations and osteological correlates for soft tissue structures that support a hypothesis of digitigrady for this taxon are compared.

Pelvic and hindlimb myology of the basal archosaur Poposaurus gracilis (archosauria: Poposauroidea)

This reconstruction is based on the direct examination of the osteology and myology of phylogenetically relevant extant taxa in conjunction with osteological correlates from the skeleton of P. gracilis and provides a foundation for subsequent examination of variation in myological orientation and function based on pelvic and hindlimb morphology, across the basal archosaur lineage leading to extant crocodilians.

Cranial remains of Poposaurus gracilis (Pseudosuchia: Poposauroidea) from the Upper Triassic, the distribution of the taxon, and its implications for poposauroid evolution

The character states of P. gracilis demonstrate that the evolution of bipedalism, the origin/loss of a dorsal ‘sail’ and the shift to an edentulous beak are complex in poposauroids.

Femoral specializations to locomotor habits in early archosauriforms

This study illuminates how the evolution of femoral morphology in early archosauriforms was functionally constrained by locomotor habit and body size, which should aid ongoing discussions about the early evolution of dinosaurs and the nature of their evolutionary “success” over pseudosuchians.

Archosauria Ornithodira Suchia Paracrocodylomorpha Loricata Theropoda Aves Allosaurus fragilis Struthiomimus sedens Struthio camelus Velociraptor monogoliensis Tyrannosaurus rex Dinosauria

Comparisons of muscle leverage supports the inference that bipedal crocodile-line archosaurs and non-avian theropods had highly convergent hindlimb myology, suggesting similar muscular mechanics and neuromuscular control of locomotion.

Deep evolutionary diversification of semicircular canals in archosaurs

...

References

SHOWING 1-10 OF 125 REFERENCES

Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira

The analysis suggests that the dentition and diet of silesaurids, ornithischians and sauropodomorphs evolved independently from a plesiomorphic carnivorous form, and Asilisaurus demonstrates the antiquity of both Ornithodira and the dinosaurian lineage.

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

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.

Basal Archosaurs: Phylogenetic Relationships and Functional Implications

Erect posture has been identified as the key adaptation (possibly associated with locomotor stamina) that resulted in the archosaurian radiation.

Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly

The phylogeny of the Crocodylotarsi was re-examined based on study of most relevant fossil material of the early non–crocodyliform members of the clade.

The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida)

This analysis produces a well-resolved phylogeny, which recovers mostly traditional relationships within Avemetatarsalia, places Phytosauria as a basal crurotarsan clade, finds a close relationship between Aetosaurian and Crocodylomorpha, and recovers a monophyletic Rauisuchia comprised of two major subclades.

Bipedal locomotion in Tropidurus torquatus (Wied, 1820) and Liolaemus lutzae Mertens, 1938.

For the first time, bipedal locomotion on South American lizards, the sand-dweller Liolaemus lutzae and the generalist Tropidurus torquatus is described.

The origin of crocodilian locomotion

The widespread distribution of apparently homologous adaptations for erect gait among the archosaurs with crocodile-normal tarsi suggests that those structures are plesiomorphic for this group, which comprises the Aetosauria, "rauisuchians," "sphenosuchians,'" Hallopus, and the Crocodylia.

Adductors, abductors, and the evolution of archosaur locomotion

Fossil theropods document the stepwise evolution of a novel mechanism of limb adduction/abduction involving long-axis rotation of the femur, which accounts for the conspicuous absence of significant musculature ventral and dorsal to the hip joint in extant birds.

The evolution of locomotion in archosaurs

Scleromochlus taylori and the origin of dinosaurs and pterosaurs

A reanalysis of crown–group archosaur relationships confirms the split into Crurotarsi (crocodile relatives) and Ornithodira (bird relatives), as well as the clear division of Ornithadira into Pterosauria and Dinosauromorpha.
...