First 'Rauisuchian' archosaur (Pseudosuchia, Loricata) for the Middle Triassic Santacruzodon assemblage zone (Santa Maria Supersequence), Rio Grande do Sul State, Brazil.

Marcel B Lacerda,Cesar L Schultz,Cristina Bertoni-Machado,Lorenzo Rook

doi:10.1371/journal.pone.0118563

Marcel B Lacerda, Cesar L Schultz + Show 2 more

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https://doi.org/10.1371/journal.pone.0118563

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Journal: PloS one	Publication Date: Feb 25, 2015
Citations: 21	License type: CC BY 4.0

Affiliation: Universidade Federal do Rio Grande do Sul

Abstract

The ‘Rauisuchia’ are a group of Triassic pseudosuchian archosaurs that displayed a near worldwide distribution. In Brazil, their fossils are found only in the Santa Maria Formation (Paraná Basin) of the Rio Grande do Sul State, specifically in the Middle Triassic Dinodontosaurus assemblage zone (AZ) and the Late Triassic Hyperodapedon AZ (Rauisuchus tiradentes). Between these two cenozones is the Santacruzodon AZ (Middle Triassic), whose record was, until now, restricted to non-mammalian cynodonts and the proterochampsian Chanaresuchus bonapartei. Here we present the first occurrence of a rauisuchian archosaur for this cenozone, from the Schoenstatt outcrop, located near the city of Santa Cruz do Sul and propose a new species, based on biostratigraphical evidence and a comparative osteological analysis.

Highlights

The ‘rauisuchians’ comprise a problematic group of Middle to Late Triassic pseudosuchian archosaurs that are traditionally bundled together due to shared similarities in cranial, pelvic and ankle morphologies, but may not represent a natural group [1,2,3,4,5]
The last 20 years have seen an increase in the number of discoveries and redescriptions e.g. [7,8,9,10,11,12,13,14,15,16,17,18,19] along with recent cladistic analyses [4, 6, 19] which have contributed to a better understanding of the diversity and relations among ‘rauisuchians’ within Archosauria
We describe the first occurrence of a ‘rauisuchian’ archosaur for the Santacruzodon assemblage zone (AZ), based on an incomplete pelvic girdle, and discuss its taxonomic status, proposing it as a new species

Summary

Introduction

The ‘rauisuchians’ comprise a problematic group of Middle to Late Triassic pseudosuchian archosaurs that are traditionally bundled together due to shared similarities in cranial, pelvic and ankle morphologies, but may not represent a natural group [1,2,3,4,5]. [7,8,9,10,11,12,13,14,15,16,17,18,19] along with recent cladistic analyses [4, 6, 19] which have contributed to a better understanding of the diversity and relations among ‘rauisuchians’ within Archosauria. The use of more taxa in recent phylogenies has contributed to a better understanding of the diversity found in these forms, their phylogenetic and taxonomic definitions still remain unclear and new studies and more complete specimens are needed to attempt to resolve many problematic topics [3, 4, 5, 6, 11].

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