Early archosauromorph remains from the Permo-Triassic Buena Vista Formation of north-eastern Uruguay.

Martín D Ezcurra,Melitta Meneghel,Graciela Piñeiro,Pablo Velozo

doi:10.7717/peerj.776

Martín D Ezcurra, Melitta Meneghel + Show 2 more

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https://doi.org/10.7717/peerj.776

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Abstract

The Permo-Triassic archosauromorph record is crucial to understand the impact of the Permo-Triassic mass extinction on the early evolution of the group and its subsequent dominance in Mesozoic terrestrial ecosystems. However, the Permo-Triassic archosauromorph record is still very poor in most continents and hampers the identification of global macroevolutionary patterns. Here we describe cranial and postcranial bones from the Permo-Triassic Buena Vista Formation of northeastern Uruguay that contribute to increase the meagre early archosauromorph record from South America. A basioccipital fused to both partial exoccipitals and three cervical vertebrae are assigned to Archosauromorpha based on apomorphies or a unique combination of characters. The archosauromorph remains of the Buena Vista Formation probably represent a multi-taxonomic assemblage composed of non-archosauriform archosauromorphs and a ‘proterosuchid-grade’ animal. This assemblage does not contribute in the discussion of a Late Permian or Early Triassic age for the Buena Vista Formation, but reinforces the broad palaeobiogeographic distribution of ‘proterosuchid grade’ diapsids in Permo-Triassic beds worldwide.

Highlights

Archosauromorpha is one of the major groups of diapsid reptiles, which includes around 10,000 species of living birds and crocodilians (Clements, 2007) and all extinct species more closely related to these extant groups than to lepidosaurs (Dilkes, 1998)
The oldest known archosauromorphs are represented by four nominal species restricted to Upper Permian rocks of Europe and Africa
The occipital condyle of most pelycosaurs possesses an extensive planar posterior surface, resulting in a sub-quadrangular structure in ventral or lateral view (Fig. 2B; but a sub-spherical occipital condyle is present in Varanops brevirostris: Campione & Reisz, 2010), the basioccipital component of the basal tubera are strongly restricted posteriorly, being approximately as long as broad (Fig. 2C), and lacks an embayment to receive the massive footplate of the stape (e.g. Dimetrodon limbatus: Romer & Price, 1940; Edaphosaurus pogonias: Romer & Price, 1940; Ophiacodon uniformis: Romer & Price, 1940; Aerosaurus wellesi: Langston & Reisz, 1981; Secodontosaurus obtusidens: Reisz, Berman & Scott, 1992; Haptodus garnettensis: Laurin, 1993; Varanops brevirostris: Campione & Reisz, 2010)

Summary

Introduction

Archosauromorpha is one of the major groups of diapsid reptiles, which includes around 10,000 species of living birds and crocodilians (Clements, 2007) and all extinct species more closely related to these extant groups than to lepidosaurs (Dilkes, 1998). The degree of anteroposterior elongation and the presence of a parallelogram-shaped centrum indicate that FC-DPV 2637 (Fig. 5; Table 2) belongs to a middle cervical vertebra after comparisons with other basal archosauromorphs (e.g. Prolacerta broomi: BP/1/2675; Proterosuchus alexanderi: NMQR 1484; Trilophosaurus buettneri: Spielmann et al, 2008).

Results

Conclusion