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

Article

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”.

Keywords

Poposaurus Lythrosuchus” Late Triassic crurotarsan Suchia “rauisuchian” 

Kurzfassung

Zwei assoziierte Teilskelette, gefunden in der Tecovas Formation auf der McCarty Ranch (MOTTU Lokalität 0690) bei Kalgary, Texas, und im Lower Petrified Forest Member der Chinle Gruppe außerhalb des Petrified Forest National Park in Arizona, sind die bisher vollständigsten Individuen vonPoposaurus gracilis und geben neue Einblicke in die Osteologie dieses seltenen Pseudosuchiers. Die neuen Funde bestätigen, dass isoliert gefundene postcranial Elemente, welche dem Holotypus-Exemplar fchlen (verschmolzene Sacralwirbel, Pubes und Ischia), korrektPoposaurus zugerechnet worden sind. Wie in “Lythrosuchus” zeigt ein Halswirbelzentrum von TTUP-10419 eine zusätzliche, dorsal gelegene Parapophysenfacette. Die Ilia der beiden beschriebenen Individuen zeigen einen charakteristisch langen und scharf klingenartigen prae-acetabularen Fortsatz. Die Morphologie der Halswirbelcentra und des prae-acetabularen Fortsatzes vonPoposaurus gracilis ist identisch mit dem des deutlich größeren Holotypus von“Lystrosuchus” langstoni. Wir betrachten beide Gattungen als Synonyme, aber erkennenPoposaurus langstoni nov. comb. als separate Art an aufgrund der Größe und dem Fehlen sowohl eines markanten Grates an der lateralen Seites des Ischiums als auch einer Grube am Proximalende des Iliums. Eine phylogenetische Analyse vonPoposaurus im Rahmen der crurotarsalen Archosaurier ergibt Belege für eine monophyletische Gruppe Poposauroidea und bestätigt die Ansicht, dass die traditionelle Zusammensetzung der “Rauisuchia” eine paraphyletische Ansammlung abgeleiteter Suchier ist.

Schlüsselwörter

Poposaurus Lythrosuchus” Obere Trias crurotarsale Archosaurier Suchia “Rauisuchia” 

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Copyright information

© E. Schweizerbart’sche Verlagsbuchhandlung 2003

Authors and Affiliations

  1. 1.Department of Biological SciencesTexas Tech UniversityLubbockU.S.A.
  2. 2.Mesalands Community CollegeTucumcariUSA

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