Abstract
ABSTRACT The braincase of the rauisuchian pseudosuchian archosaur Arizonasaurus babbitti, from the Middle Triassic of the western United States, is described from two specimens. There are no obvious braincase autapomorphies and most of the other braincase features of A. babbitti are plesiomorphic for pseudosuchians/crurotarsans. The results of phylogenetic analyses of archosaurian braincase characters indicate that A. babbitti is not especially closely related to other rauisuchians for which braincase anatomy is known (Batrachotomus kupferzellensis, Saurosuchus galilei, Postosuchus kirkpatricki, Tikisuchus romeri). Given that A. babbitti is a member of a clade that includes Poposaurus and chatterjeeids to the exclusion of most other rauisuchians, braincase data suggest that Rauisuchia are not monophyletic. This is in accordance with a recent appraisal of non-braincase data but, in contrast, our analyses suggest that Poposaurus and its closest allies are more distantly related to Crocodylomorpha than are other rauisuchians.
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