The Poposauridae were large carnivores closely related to the Crocodylomorpha ( Crocodiles and their kin). At least some forms were bipedal or capable of bipedal locomotion, much like the large theropod dinosaurs of the Jurassic and Cretaceous.
One paleontologist, Sankar Chaterjee of Texas Tech University, has even suggested that the Poposaurs were directly ancestral to the Tyrannosaurs [S. Chaterjee, 1985, "Postosuchus, a new thecodontian reptile from the Triassic of Texas and the origin of Tyrannosaurs"; Phil. Trans. R. Soc. Lond. B. 309, 395-460]. Certainly there are a number of extraordinary similarities between the two, as indicated for example by the form of the skull (shown here) and pelvis (hip-bone). Chaterjees' conclusion has been rejected by his co-workers, who point out that Postosuchus had a crocodile-like, rather than a dinosaur-like, wrist/ankle structure [Philip A. Murry, "Vertebrate Paleontology of the Dockum Group" in The Beginning of the Age of Dinosaurs, ed. Kevin Padian, Cambridge University Press, 1986; p.124].
What seems more likely is that creatures like Postosuchus were an example of parallel evolution, the same kind of creature evolving to fill the same ecological role; a morphogenetic preview of the large theropod archetype of the great dinosaurian carnivores of the later Mesozoic.
Length: 4.5 metres
Howard Post County., Texas, USA
|- Poposauridae - Links -||
Rauisuchia Translation and Pronunciation Guide - more than what the title indicates, this is an excellent description of every known genus of Prestosuchid, Rauisuchid, and Poposaurid thecodontian. Includes a sound file (.au) giving the correct pronounciation of each name. Unfortunately does not distinguish between Rauisuchidae and Prestosuchidae. Mirror site
Re: Postosuchus/Rauisuchus - Thomas R. Holtz, Jr.
Michael J. Benton, 1984, "Rauisuchians and the success of dinosaurs"; Nature, vol 310, p. 101
Palaeos Page (incorporates some of this material, plus a lot of additional material)