New insights into vertebrate assemblages from the lower Chañares Formation (Ladinian−earliest Carnian, Ischigualasto−Villa Unión Basin), northwest Argentina

JULIA DESOJO; MARTIN EZCURRA; LUCAS FIORELLI; AGUSTIN MARTINELLI; JEREMIAS TABORDA; BELEN VON BACZKO; MARTIN HECHENLEITNER; MIGUEL EZPELETA ; TROTTEYN; SOLEDAD GOUIRIC-CAVALLI

Congreso; 13th Annual Meeting of the European Association of Vertebrate Palaeontologists; 2015

The Triassic witnessed the origin or early evolutionary radiation of multiple amniote clades, such as lepidosauromorphs, rhynchosaurs, archosaurs, turtles, and mammaliaforms. The major diversification of these lineages started during the Middle Triassic and the continental outcrops of the Chañares Formation (NW Argentina) are among the best that document this event worldwide. Recent fieldworks in the lowermost levels of the Chañares Formation at the type and three new localities (Brazo del Puma, El Torcido and Campo Córdoba) yielded unknown vertebrate groups and considerably improved the knowledge of other clades for this unit. We report for the first time the presence of lobe-finned fishes (Sarcopterygii, Actinistia), being represented by a fragment of skull roof. Among amniotes, several non-hyperodapedontine rhynchosaurid, doswelliid archosauriform and dicynodont partial skeletons were collected within the first five metres of the formation. The absence of proterochampsids and dinosauromorphs in the first 5 metres of the Chañares Formation suggests a different faunal association to that previously known from the upper levels of the lower member of the unit (e.g. Chañares type locality). The study of the lowermost levels of the Chañares Formation bridges a crucial gap between the well-known early Middle Triassic assemblages of southern Pangaea (e.g. the Manda beds of Tanzania, Yerrapalli Formation of India) and the younger type Chañares fauna and the Dinodontosaurus Assemblage Zone of southern Brazil. This more comprehensive knowledge of the faunal associations of Pangaea will shed light on the flourishing of archosaurs during the Late Triassic and subsequently later in the Mesozoic.