CRANIAL MORPHOLOGY OF THE LATE TRIASSIC SOUTH AMERICAN ARCHOSAUR NEOAETOSAUROIDES ENGAEUS: EVIDENCE FOR AETOSAURIAN DIVERSITY

Abstract

The cranial anatomy of Neoaetosauroides engaeus Bonaparte, 1969 from the upper part of the Los Colorados Formation, western Argentina, is addressed herein. This description is based on material collected recently, which permits a complete restoration of the skull; previously, a partial lower jaw and premaxillary and maxillary fragments were the only cranial remains known. Unlike other aetosaurs for which the premaxillary dentition is known, in N. engaeus the upper tooth row extends anteriorly to reach near the expanded tip of the snout; this condition is not compatible with the presence of a keratinous beak previously suggested for other aetosaurs. The conical shape of the teeth of N. engaeus differs from the slightly compressed teeth of Desmatosuchus, Stagonolepis and Typothorax, and the distinctly recurved teeth of Aetosaurus and Aetosauroides. This diversity of dental morphology suggests a variety of food‐item preferences among aetosaurs.

The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades

“…In the aetosaurs Longosuchus (TMM 31185-98), Aetosaurus (SMNS 5770), Stagonolepis (Walker, 1961), Neoaetosauroides (Desojo and Baez, 2007), Aetosauroides (Casamiquela, 1961), and Desmatosuchus (Small, 2002), the supratemporal fenestrae open more laterally than dorsally. The supratemporal fenestrae open dorsally in Revueltosaurus .…”

“…However, in the suchians Arizonasaurus (UCMP 36232; Nesbitt, 2005a) and Effigia (AMNH FR 30587; Nesbitt, 2007) and the aetosaurs Aetosaurus (Schoch, 2007), Desmatosuchus (TTU-P 9024; Small, 2002), Stagonolepis (Walker, 1961), and Neoaetosauroides (PVL 4363; Desojo and Baez, 2007) the maxilla creates part of the posterior border of the external naris.…”

“…Taxa known from disarticulated and incomplete orbital regions should be scored as unknown. At this point, Aetosaurus (Schoch, 2007), Neoaetosauroides (Desojo and Baez, 2007), Saurosuchus (PVSJ 32), Postosuchus kirkpatricki (TTU-P 9000), Postosuchus alisonae (UNC 15575), Polonosuchus silesiacus (ZPAL Ab III/563), Hesperosuchus ''agilis'' (Clark et al, 2000), Junggarsuchus sloani , and crocodyliforms can be scored as having palpebral(s) among non-crocodyliform crocodylian-line archosaurs.…”

The evolution of jaw mechanism and dental function in heterodont crocodyliforms

“…For example, various members of the Stagonolepididae (aetosaurs) show a complex dentition with labiolingually flattened, serrated teeth which, though the dentition is mostly homodont, bear some degree of dental wear (e.g. the anterior maxillary teeth of Stagonolepis, Walker 1961 or different teeth of other members of the clade, Desojo and Báez 2007). Walker (1961:134) suggested that "the crowns of the dentary teeth met the medial ones of the maxillary teeth in a slicing action".…”

A large archosauriform tooth with multiple supernumerary carinae from the Upper Triassic of New Mexico (USA), with comments on carina development and anomalies in the Archosauria

“…Among other Late Triassic archosaurs, it is obviously not the tooth of an aetosaur as these possibly herbivorous archosaurs have a reduced and secondarily generalised dentition (e.g. Heckert and Lucas 2000a;Desojo and Ba´ez 2007). Triassic theropod dinosaurs, even larger, younger taxa such as Liliensternus (teeth are not yet known from Gojirasaurus), are too small to yield such teeth (Carpenter 1997;Heckert and Lucas 2000b; A.B.…”