Arizonasaurus

Arizonasaurus was a ctenosauriscid archosaur from the Middle Triassic (243 million years ago).[1] Arizonasaurus is found in the Middle Triassic Moenkopi Formation of northern Arizona. A fairly complete skeleton was found in 2002 by Sterling Nesbitt. The taxon has a large sailback formed by elongate neural spines of the vertebrae. The type species, Arizonasaurus babbitti, was named by Samuel Paul Welles in 1947.

Discovery and naming
The type species, Arizonasaurus babbitti, was named by Samuel Paul Welles in 1947 on the basis of a few teeth and a maxilla, labelled as specimen UCMP 36232.[2] A fairly complete skeleton was found in 2002 by Sterling Nesbitt.

Description
It had a sail made of tall neural spines, that was similar to those of other basal archosaurs like Ctenosauriscus, Lotosaurus, Bromsgroveia, and Hypselorhachis.

Braincase
Arizonasaurus is described from two specimens of braincases. Some ancestral features of the braincase of Arizonasaurus are plesiomorphic for crurotarsans.

Distinguishing characteristics
Below is a list of characteristics found by Nesbitt in 2005 that distinguish Arizonasaurus:[4]
 * a deep fossa hidden from view on the posteroventral edge of the upward-pointing process of the maxilla;
 * and a tongue-groove attachment between the pubis and the ilium.