Arizonasaurus

Lore & Background

Arizonasaurus is described from two braincase specimens, which show some ancestral features plesiomorphic for crurotarsans. Characteristics distinguishing Arizonasaurus include 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.

Reader's Guide

Arizonasaurus is significant as a Middle Triassic ctenosauriscid archosaur that helps clarify the early evolution of pseudosuchians. Its presence in the Moenkopi Formation suggests that the divergence of birds and crocodiles occurred earlier than previously thought. The ctenosauriscids, including Arizonasaurus, allow the distribution of Triassic faunas to be more widespread across Europe, Asia, North America, and Africa. The fauna of the Moenkopi Formation represents a stage transitional between older and younger faunas. Phylogenetic analysis places Arizonasaurus close to Ctenosauriscus, and together with other genera they form Ctenosauriscidae, which are more derived than rauisuchians. The pelvic girdle of Arizonasaurus unites it with Ctenosauriscus, Lotosaurus, Bromsgroveia, and Hypselorhachis, and newly identified pseudosuchian features support a monophyletic group including poposauroids and ctenosauriscids.

Did You Know?

• Arizonasaurus means 'Arizona reptile'.
• A fairly complete skeleton (~50%) was found in 2002 by Sterling Nesbitt.
• Its sail was similar to those of Ctenosauriscus, Bromsgroveia, and Hypselorhachis.