Poposaurus

Poposaurus, live reconstruction

• Wyoming ( Popo Agie - Formation)
• Arizona, Utah ( Chinle Formation)
• Texas ( Tecovas lineup, Cooper Canyon Formation)

• Poposaurus gracilis (Flour, 1915)
• Poposaurus langstoni ( Long & Murry, 1995)

Poposaurus is an extinct genus of archosaurs from the group of Crurotarsi that lived during the Late Triassic in North America. She is the namesake representatives of Poposauroidea, a relative of the crocodile group. So far, two species of this genus have been described: the type species Poposaurus gracilis and Poposaurus langstoni, the latter was originally known as Lythrosuchus. Although traditionally depicted as an ongoing, four-legged, recent studies prove that it was an obligate bipedal running ( bipedes ) animal. Poposaurus is named after the Little Popo Agie River in Wyoming, on the shores near the town of Lander, the first fossils were discovered.

Features and bipedalism

Poposaurus is estimated to have a length of 4 m and a weight of about 100 kg. Already Maurice G. flour ( 1915) conjectured that Poposaurus at least temporarily bipedal running ( bipedalism ), although this animal is usually shown in the following descriptions as a quadruped ( four-legged running). Only in 2011 it was proven that Poposaurus an obligate biped ( two-legged mandatory ) actually was. This bipedalism was probably a development of the semi- upright walking his quadrupedal ancestors, which is still seen in living crocodiles. The bipedal locomotion of Poposaurus be found in similar form in dinosaurs. However, in contrast to dinosaurs his hind legs under the body were columnar ( pillar - erect ): So the acetabulum showed ( acetabulum ) down the leg so was like a pillar directly below the hip. At dinosaurs the acetabulum showing the outside ( Buttress erect ), wherein the head of the femur in the acetabulum showing the side.

From related genera is Poposaurus be based on features of the ilium ( ilium ) differ: This has a long and low iliac blade ( iliac blade ) while the praeacetabulare extension ( a forwardly directed outgrowth ) shovel-shaped and the postacetabulare extension ( one after proximally directed outgrowth ) was extended like wings, similar to theropods.

Finds

Poposaurus was described by Maurice G. flour in 1915 for the first time scientifically, based on a fragmentary skeleton ( holotype, specimen number CFMNH UR357 ) consisting of two vertebrae, a caudal vertebra, the left iliac bone ( ilium ), the upper part of the left thigh bone ( femur ), the right thigh bone, and the lower part of the seat bone ( ischium ) is.

Since the initial description more fragmentary skeletons have been found, mostly consist only of pelvic bones, vertebrae and leg bones. The most complete skeleton to date ( copy number YPM 57100 ) is missing only the skull. The type species Poposaurus gracilis was discovered in the western United States and dates from the Popo Agie - Formation of Wyoming, from the Chinle Formation of Arizona and Utah, as well as from the Tecovas formation of Texas. The second type, Poposaurus langstoni, meanwhile, comes from the Cooper Canyon Formation of Texas.

System

Inside systematics

Another way Poposaurus langstoni was first described by Long and Murry (1995 ) described as a distinct genus - Lythrosuchus. A redescription of Poposaurus fossils, however, revealed that there probably is a second type of Poposaurus.

Outer systematics

Poposaurus fossils have been known for over 100 years, with the systematic classification because of only fragmentary discoveries was long unclear. So Poposaurus was already a bird Beck dinosaurs ( Nopsca, 1921), as Stegosaurus ( Huene, 1950), as well as a theropod (1961 Colbert ) described. Only Walker (1969 ) recognized that it was a pseudosuchiden Crurotarsi, a related to today's crocodiles, archosaurs. Newer copies of Poposaurus gracilis and other close related genera confirm the relationship with the Pseudosuchia ( Galton, 1977; Long and Murry, 1995; Nesbitt and Norell, 2006; Weinbaum and Hungerbuhler, 2007).

Poposaurus is the eponymous representative of Poposauridae and Poposauroidea. Both groups are considered by many researchers as identical, thus the name Poposauridae is rarely used. Traditionally, the Poposauroidea up a group of Rauisuchia - but recent studies suggest that the Rauisuchia are paraphyletic, so do not include all the descendants of an ancestor. The relationships within the Poposauroidea are unclear as possible with close relatives who are Shuvosaurus, Sillosaurus and Arizonasaurus.

It follows a recent cladogram example of Nesbitt (2011):

Qianosuchus

Arizonasaurus

Xilousuchus

Poposaurus

Lotosaurus

Sillosaurus

Shuvosaurus

Effigia