An examination of non-mammalian cynodont cranial endocasts

English: The palaeoneurology (study of the nervous system of extinct animals) of nonmammalian cynodonts, which were the ancestors of mammals, is poorly understood. It is thought that the relative brain size of cynodonts increased with time, and that this change significantly affected their physiology and behaviour. Forty-four cynodont skulls belonging to eleven genera from Permian, Triassic and Jurassic strata were scanned and analysed using neutron computerized tomography (NCT), at the SAFARI-1 Nuclear Research Reactor of the Nuclear Energy Corporation of South Africa (Necsa). Data concerning the endocranial casts was hereby obtained in a non-destructive manner. Four specimens, namely Galesaurus, Platycraniellus, Langbergia and Tritylodon produced successful scans and were used for further study. Measurements of the cranial material were used to calculate the size of the brain endocasts and the approximate body masses were determined from an equation using skull length. The encephalization quotient (EO), a measure of brain size relative to body size, was determined for each specimen using brain volume and body mass. Changes in the position of the brain inside the skull, and an overall increase in size of the brain in the more derived cynodonts indicate some development towards the mammalian condition. Taxonomic variation regarding the shape and size of the olfactory bulbs and other parts of the brain endocasts is discussed and related to differences in ecology or behaviour. The relatively deep and large olfactory bulbs in some cynodonts may be an adaptation to either nocturnal behaviour, dietary or habitat preferences. Relatively large cranial endocasts in Galesaurus, Platycraniellus, Massetognathus, Tritylodon, Chiniquodon and the tritheledonts may be related to habitat preference or social behaviour. The basal epicynodonts Galesaurus and Platycraniellus have the largest cranial endocasts of all the cynodonts studied. Their large cranial endocasts may be related to behavioural or ecological preferences, but the results require confirmation from a larger sample size. The present study provides an important foundation from which further cranial endocast studies on cynodonts can be developed.