South American Crocodylomorphs (Archosauria; Crocodylomorpha): a review of the early fossil record in the continent and its relevance on understanding the origins of the clade

Abstract

Crocodylomorpha is a clade that has its origins during the Late Triassic and attained a global distribution early in their radiation. In this context, although limited to few geological units, the South American record has been relevant in the understanding of the origins of the clade. Additionally analyzing the South American crocodylomorph record and comparing it with the one in the rest of Pangea is relevant as, in recent years, provincialism has been proposed for different faunal assemblages. In this contribution we review the crocodylomorph Triassic record in South America by analyzing three units that have yielded fossils of the clade: the Santa María Supersequence in Brazil; and, the Ischigualasto and Los Colorados formations in Argentina. Our review does not support previous assignments of the taxon Barberenasuchus from the Santa María Supersequence as a non-crocodyliform crocodylomorph, as it displays traits that are absent in all known crocodylomorphs and are present in other earlier branching archosaurs. On the other hand, the Argentinian stratigraphic units remain as the only ones that have crocodylomorphs in the subcontinent. Here we report for the first time the occurrence of “large-bodied” crocodylomorphs in the Ischigualasto Formation, represented by a new yet undescribed taxon. The Los Colorados Formation has a diverse crocodylomorph record being represented by a non-crocodyliform crocodylomorph (Psedhesperosuchus) and two crocodyliforms (Hemiprotosuchus and Coloradisuchus). Here we present a putative new non-crocodyliform crocodylomorph taxon from Los Colorados Formation. When compared with other crocodylomorph bearing formations around Pangea, the Ischigualasto Formation bears similarities with the crocodylomorphs assemblages of North America due to the presence of early branching crocodylomorphs (Trialestes) including “large-bodied” taxa. The Los Colorados Formation reveals a transitional composition corresponding to Norian and Early Jurassic assemblages of Pangea, as it shares the presence of basal crocodyliforms (i.e., protosuchids) typical of Early Jurassic units (e.g., Upper Elliot) and basal non-crocodyliform crocodylomorphs, widely present in Norian assemblages.