The origins and early diversity of social behaviour in mammalian ancestors

Reconstructing ancient behaviour is crucial to better grasping the evolutionary origins of mammals; however, fossilised evidence of behavioural complexity is elusive. Here we propose to use SRµCT to describe and compare the cranial bone histology, brain, nerves and inner ear of a carefully selected sample of mammalian ancestors (therapsids), which display a diversity of head ornamentations (horns, bosses, enlarged canines, etc.) that suggests male to male combat, face biting, and sexual display. Improved knowledge of the adaptations of the nervous system and cranial structure to withstand those fights will provide, for the first time, insight into the diversity of complex social behaviours in therapsids. This will be accompanied by a study of brain size to address whether sociality had an effect on encephalisation. This study has the potential to highlight the existence of complex social behaviours many millions of years before the origin of mammals.