A new aetosaur (Reptilia: Archosauria) from the Upper Triassic of Texas and the phylogeny of aetosaurs

Abstract

ABSTRACT Coahomasuchus kahleorum, gen. et sp. nov. is a small (<1 m long) aetosaur from the Upper Triassic Colorado City Member of the Dockum Formation in West Texas. The holotype consists of a nearly complete articulated skeleton, including a well-preserved dorsal and ventral carapace. Several postcranial features diagnose Coahomasuchus, including: dorsal paramedian plates considerably (3.25:1) wider than long, unflexed, lack keels or horns, and bear faint sub-parallel to radial ornamentation, and lateral scutes that are also unflexed, flat, and bear a faint radial pattern of pits and grooves. Coahomasuchus co-occurs with the aetosaur Longosuchus and the phytosaurs Angistorhinus and Paleorhinus, indicating that it is of Otischalkian (early late Carnian) age. Detailed phylogenetic analysis reveals that several North American aetosaur taxa are junior subjective synonyms of previously named taxa. Lucasuchus was named from material from the type locality of Longosuchus and is a junior subjective synonym of that taxon. Acaenasuchus is known only from localities that also produce Desmatosuchus and probably represents juvenile individuals of Desmatosuchus. Stegomus, from various localities in the Newark Supergroup, is a junior subjective synonym of Aetosaurus, known previously from the German Keuper and Upper Triassic strata in Italy and Greenland. Paratypothorax andressi is properly called P. andressorum and is known from strata of Adamanian (latest Carnian) to Apachean (Rhaetian) age.