CHARACTERS AND ANATOMY
 

The dinocephalians were in many ways the most archaic of the higher therapsids and although these reptiles showed therapsid adaptations such as the expansion of the ilium and the general pose of the limbs, they retained various primitive characters of the pelyosaurs. For example they had no secondary palate and their dentary bone was of moderate size (in the more mammal-like and advanced group, the Cynodonts the dentary bone of the lower jaw grew increasingly large, until it constituted the entire jaw, which is the mammalian condition).

All dinocephalians (to varying degrees) featured pachyostosis, a great thickening of the bones on the top of the skull, which increased as the animal grew into adulthood. Using comparisons to extant taxa it is suggested that this feature was used in head-butting contests with the main force of the butt hitting the thickened dorsal shield of the skull and transmitting round the sides along thickened girders of bone to the neck, thus proecting the brain. The shock then passed onto the heavily muscled shoulders which provided much of the force for the initial charge (see picture below). However, these dinocephalian jousts would have been relatively sedate affairs and resemble a pushing contest.

 

Demonstrating the distribution of the forces acting on the skull during head butting (taken from The Therapsida Website - see Links page)

 

All Dinocephalians are distinguished by interlocking incisor or front teeth and a distinctly down-turned facial region. The synapsid opening for the attachment of jaw muscles remained relatively small so it is assumed that the power of the bite was provided by the sheer mass of the animals jaw. The apparatus of the jaw mechanism is shown below.

The lower jaw opens and closes with a simple hinge movement (adapted from Efremov, 1940).

The elaboration of the herbivorous incisors meant they had a degree of crushing or grinding ability (see picture below). The size of the crown was reduced and therefore their ability to tear up fleah was diminished.

 

Lower incisor of the tapinocephalidae (adapted from Efremov, 1940).