Anatomy and phylogenetic affinities of a new silesaurid assemblage from the Carnian beds of south Brazil

ABSTRACT

New specimens and the reassessment of many silesaurids have recently shed light on the origin and early evolution of dinosaurs and their close relatives. Yet, the group is relatively poorly represented in South America, an area that likely played an important role in dinosaurian origins. Since the discovery of Sacisaurus agudoensis from the Norian Caturrita Formation, only the fragmentary Gamatavus antiquus and Amanasaurus nesbitti have been reported from the Triassic of south Brazil. Here we describe disarticulated silesaurid remains from Waldsanga, one of the most important tetrapod-bearing localities of the Santa Maria Formation, which represent the second Carnian occurrence of the group in Brazil. The postcranial elements exhibit a combination of dinosauromorph symplesiomorphies and silesaurid diagnostic traits, showing that a conservative anatomy is pervasive among early dinosauromorphs. We also conducted a set of exploratory analyses to infer the phylogenetic relations of the new occurrence and the robustness of some of the most recent phylogenetic hypotheses in face of the increasing diversity of Silesauridae. This revealed a rather uncertain evolutionary scenario not only for Silesauridae, but for early dinosauromorphs in general.

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DATA AVAILABILITY STATEMENT

The raw CT-scan data are available in the following repository: https://doi.org/10.5281/zenodo.7939011

ACKNOWLEDGMENTS

We thank researchers, collection managers, and curators who provided access to the collections under their care, namely: A. Downs, A.M. Ribeiro, A. Silveira, C. Apaldetti, C. Schultz, C. Revuelta, F. Abdala, F. Novas, F. Pretto, G. Cisterna, G. Gurtler, J. Ferigolo, L. Haerter, L. Kerber, M. Ezcurra, M. Caldwell, M. Stocker, P. Ortíz, P. Hernández, R. Müller, R. Martínez, and S. Cabreira. Thanks also to V. Yarborough, Paleontology Laboratory Manager at Virginia Tech, who accurately improved the preparation of the fossils, and to R. Piechowski, University of Warsaw, for giving permission to use one photo of the Silesaurus opolensis maxilla. Thanks to D. Casali for his help, tips, and suggestions with Mesquite and TNT software. The authors also acknowledge the support provided by Centro para Documentação da Biodiversidade, FFCLRP, Universidade de São Paulo, Brazil, regarding the use of the CT-scan (computed tomography) machine. Thanks to the JVP editors M. D'Emic (Senior Editor), D. Schwartz (Editor, Journal of Vertebrate Paleontology), P. Godoy (Phylogenetics Editor, Journal of Vertebrate Paleontology), and two anonymous reviewers. Finally, the authors acknowledge the São Paulo Research Foundation (FAPESP), Coordination for the Improvement of Higher Education Personnel (CAPES), National Council for Technologic and Scientific Research (CNPq), and the National Science Foundation (NSF) EAR for funding this research.

The São Paulo Research Foundation awarded grants to Gabriel Mestriner (FAPESP 2022/00171-9, 2019/07510-0, and 2018/24031-6), to Júlio Marsola (FAPESP 2021/14560-4), and to Max Langer (FAPESP 2020/07997-4). Coordination for the Improvement of Higher Education Personnel supported Júlio Marsola (CAPES 88887.572782/2020-00). The National Council for Technologic and Scientific Development supported Átila Da-Rosa (CNPq 303972/2021-1). The National Science Foundation supported Sterling Nesbitt (NSF 1349667).

AUTHOR CONTRIBUTIONS

JCAM and AASDR played significant roles in the discovery and excavation of the fossil during a joint fieldwork expedition in 2014, which was conducted by the Laboratório de Paleontologia (Universidade de São Paulo—USP, Ribeirão Preto) and the Laboratório de Estratigrafia e Paleobiologia (Universidade Federal de Santa Maria—UFSM, Santa Maria). GM, JCAM, and ML designed the project. GM and SJN performed the mechanical preparation of the fossils. GM conducted the anatomical descriptions, created the figures, and drafted the manuscript. GM and JCAM carried out the phylogenetic analysis. AASDR contributed valuable geological information. All authors actively participated in editing the manuscript and engaging in fruitful discussions regarding the data, results, and implications of the new silesaurid specimen.

LIST OF SUPPLEMENTARY FILES

SUPPLEMENTAL DATA (APPENDICES S1 AND S2).

Matrix of Ezcurra et al., 2019: TNT and NEXUS files. Plus, MPTs of the parsimony analyses: 1, MPTs—Ezcurra et al., 2019—analysis corresponding to Fig. 3 of the supplementary material; 2, MPTs—Ezcurra et al., 2019—analysis corresponding to Fig. 16A of the Main Document; 3, MPTs—Ezcurra et al., 2019—analysis corresponding to Fig. 16B of the Main Document TNT file: Ezcurra et al., 2020.

Matrix of Muller & Garcia 2020: TNT and NEXUS files. Plus, MPTs of the parsimony analyses: 1, MPTs—Muller & Garcia 2020—Analysis corresponding to Fig. 16C; 2, MPTs—Muller & Garcia 2020—Analysis corresponding to Fig. 16D.

Raw images of the histology (Fig. 15): 1, Raw data—histology—Corresponding to Fig. 15C; 2, Raw data—Histology—Corresponding to Fig. 15D; 3, Raw data—Histology—Corresponding to the Fig. 15E.

Correction Statement

This article was originally published with errors, which have now been corrected in the online version. Please see Correction (http://dx.doi.org/10.1080/02724634.2023.2254075)