Brain endocast of two non-mammaliaform cynodonts from southern Brazil: an ontogenetic and evolutionary approach

ABSTRACT

Computed tomography is a non-destructive method that facilitates the accurate analysis of the internal structures of fossils. Several paleoneurological studies concerning derived non-mammaliaform cynodonts, mammaliaforms and basal mammals using this technique have been published. However, little remains known regarding the brain anatomy of basal Cynodontia. Thus, it is relevant to increase knowledge concerning the basal members of this clade to obtain a better understanding of brain evolution during the descent of mammals from non-mammaliaform cynodonts. Therefore, the present study involved analysing the digital endocasts of two non-mammaliaform cynodonts (Probelesodon kitchingi and Massetognathus ochagaviae). To assess the rate of brain development, the encephalisation quotients for these species were calculated and compared with previous data. Compared to a previous study on the brain endocasts of Probelesodon sp. and Massetognathus sp. from Argentina, digital endocasts of the Brazilian specimens revealed new brain morphology features for these genera. Additionally, the 3D digital endocasts and EQ estimates are relevant for assessing intraspecific variation and possible ontogenetic changes in these fossil taxa.

KEYWORDS:

• Brain evolution
• cynodontia
• encephalization quotient
• triassic

Acknowledgments

The authors are indebted to João Borges and Dario Anschau, from Instituto do Cérebro (InsCer/PUCRS), for providing access to the medical CT-scan and for showing interest on palaeontological research. Vanessa Macedo and Jayme Marques (MCT-PUCRS) provided help with text revision and software use. Drs. Ana Maria Ribeiro (FZB), Cesar L. Schultz (UFRGS) and Julia B. Desojo (MLP) provided helpful comments to the original Msc volume of CAH. We also thank the modifications suggested by the blind reviewers that significantly allowed to improve the quality of this paper. CAH received an MSc scholarship from CNPq (2016–2018), and is currently funded by a CAPES PhD scholarship.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary Material

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Additional information

Funding

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico [830432/1999-0]; Paleontological Society [PalSIRP Sepkoski Grant 2016]