A new proterochampsid Chanaresuchus ischigualastensis (Diapsida, Archosauriformes) in the early Late Triassic Ischigualasto Formation, Argentina

Abstract

The proterochampsids are a group of crocodile-like archosauriforms usually considered as one of the potential successive sister taxa of the crown group Archosauria (e.g., Sereno and Arcucci,1990; Sereno, 1991; Dilkes and Sues, 2009; Ezcurra et al., 2010). The clade is currently endemic to the late Middle and early Late Triassic of South America. The best-known proterochampsids come from the Cha ˜ nares and Ischigualasto formations, which belong to the Ischigualasto-Villa Union Basin (Fig. 1), which formed during the breakup of Gondwana (Uliana and Biddle, 1988; Ramos and Kay, 1991). The tetrapod assemblage from the Chanares Formation (Anisian–early Carnian; Desojo et al., 2011) has been usually interpreted to differ from that of the Ischigualasto Formation (late Carnian–earliest Norian; Mart´ınez et al., 2011), and this traditional view also applies for proterochampsids. In the Cha ˜ nares Formation, the proterochampsid genera Chanaresuchus, Gualosuchus, and Tropidosuchus (Romer, 1971, 1972; Arcucci, 1990) are documented, whereas in the Ischigualasto Formation only the genus Proterochampsa has been reported (Reig, 1959). The latter highlighted a complete replacement at a generic level among these proterochampsid assemblages in southwestern Pangaea. However, an almost complete proterochampsid skeleton from the Late Triassic Ischigualasto Formation is given a preliminarily description here and assigned to the traditionally Middle Triassic genus Chanaresuchus (cf. Sill et al., 1994). Accordingly, the new proterochampsid record reported here changes the pattern of macroevolutionary history of the group during the Middle to Late Triassic in southwestern Pangaea.