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[dinosaur] Lower Triassic age for Sanga do Cabral Formation in South America based on parareptile Procolophon




Ben Creisler
bcreisler@gmail.com

A recent paper not yet mentioned:


Sérgio Dias-da-Silva, Felipe L. Pinheiro, Átila Augusto Stock Da-Rosa, Agustín G. Martinelli, Cesar L. Schultz, Eduardo Silva-Neves & Sean P. Modesto (2017)
Biostratigraphic reappraisal of the Lower Triassic Sanga do Cabral Supersequence from South America, with a description of new material attributable to the parareptile genus Procolophon.
Journal of South American Earth Sciences (advance online publication)
https://doi.org/10.1016/j.jsames.2017.07.012
http://www.sciencedirect.com/science/article/pii/S0895981117302304

Highlights

An extensive, comprehensive, and up-to-date multidisciplinary review which also includes new paleontological information regarding the Western Gondwanan Sanga do Cabral Supersequence (SCS).

A detailed discussion of all available geological and paleontological data of the SCS with a comparison to the Argentinean Talampaya, Tarjados, and Puesto Viejo Formations.

A discussion regarding the biostratigraphic correlation of Lower Triassic units from South America with those from South Africa (Katberg Formation of the Karoo Basin).

A geological and paleontological framework that provide compelling evidence for a Lower Triassic age for the Sanga do Cabral Formation, which includes the Sanga do Cabral Formation from Brazil and the Buena Vista Formation form Uruguay.

An investigation of the largest Procolophon trigoniceps so far collected in Gondwana (UFSM 11409a), with its inclusion in a phylogenetic dataset, in order to test its previous taxonomic assignment based upon morphology, an also of isolated vertebrae and mandibular fragments that are consistent in size with UFSM 11409a.

Abstract

The Sanga do Cabral Supersequence (SCS), comprises the Brazilian Sanga do Cabral Formation (SCF) and the Uruguayan Buena Vista Formation (BVF). So far, the SCS has yielded temnospondyls, parareptiles, archosauromorphs, putative synapsids, and a number of indeterminate specimens. In the absence of absolute dates for these rocks, a biostratigraphic approach is necessary to establish the ages of the SCF and the BVF. It is well established that the SCF is Early Triassic mainly due to the presence of the widespread Gondwanan reptile Procolophon trigoniceps. Conversely, the age of the BVF is subject of great controversy, being regarded alternatively as Permian, Permo-Triassic, and Early Triassic. The BFV has yielded the definite procolophonid Pintosaurus magnidentis. Procolophonoidea is one of the most diverse and conspicuous terrestrial tetrapod groups of the Lower Triassic Lystrosaurus Assemblage Zone in the Karoo Basin of South Africa, which preserves tetrapods from the aftermath of the end-Permian extinction event. Based on a previous interpretation that the fauna of the BVF is Permian, and in the reinterpretation of disarticulated vertebrae from SCF with ‘swollen’ neural arches as belonging to either seymouriamorphs or diadectomorphs, it was recently suggested that at least part of the SCF is Permian in age, which prompted this comprehensive reevaluation of both SCS's faunal content and geology. Moreoever, new, strikingly large procolophonid specimens (skull, vertebra, and a mandibular fragment) from the SCF are described and referred to the genus Procolophon. The large procolophonid vertebra described here contradicts the recent hypothesis that similar specimens from the SCF belong to seymouriamorphs or diadectomorphs, because its morphology is consistent with that found in Procolophon. There is not a single diagnostic specimen that supports the inference of Permian levels in the SCS. Accordingly, because all diagnostic and biostratigraphically informative fossils from the SCF and the BVF are either Early Triassic or restricted to the Triassic, we conclude that the available biostratigraphic data reinforce an Early Triassic age assignment to the SCS.