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

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. [ABSTRACT FROM AUTHOR]