Dinocephalia

Lore & Background

Dinocephalians were generally large in size, and some were the largest animals of the Permian period, and the first synapsids to reach a body size around one tonne. Their skulls and lower jaws are unified by several characters, including loss of the vomerine process of the premaxilla, enlarged temporal fenestra, and a long posteriorly directed spur-like process of the premaxilla between the nasal bones. Most dinocephalians also developed a thickened and ornamented skull roof and braincase, sometimes with horn-like projections, making their skulls highly strong and resistant to fracture. All dinocephalians are characterized by interlocking incisor teeth, and in tapinocephalids all teeth interlock. Dinocephalians ancestrally have a pair of enlarged 'canine' teeth, though in some these are absent. The teeth generally have a pointed 'talon' and a 'heel' morphology, best developed in tapinocephalids.

Reader's Guide

Dinocephalians were the first non-mammalian synapsids to be scientifically described, with remains first reported in the 19th century from Russia and South Africa. They occupied a range of ecologies, with anteosaurs being carnivores and tapinocephalians including herbivores and omnivores. During the Middle Permian, they were dominant megaherbivores and apex predators. It has been disputed whether some dinocephalians were semi-aquatic like hippopotamuses. It has been widely suggested that tapinocephalids engaged in head-butting, and other dinocephalians may have also engaged in head butting, biting, and/or head interlocking or swiping combat. Many dinocephalians appear to have had an enlarged brain cavity, which may have hosted thick protective tissue surrounding the brain, possibly helping absorb blows from head-on combat. This has led authors to suggest at least some dinocephalians, particularly tapinocephalids, had complex, gregarious social behavior, though others may have been solitary. Their fossils provide key insights into the evolution of therapsids and the ecosystems of the Middle Permian.

Did You Know?

• Dinocephalians were the first non-mammalian therapsids to be scientifically described, with remains first reported in the 19th century from Russia and South Africa.
• The dinocephalian Estemmenosuchus is one of the few non-mammalian therapsids with preserved skin impressions, showing scaleless skin covered in small tubercles.
• Some dinocephalians, like the tapinocephalid Tapinocaninus, had as few as seven caudal vertebrae, while some anteosaurs had over 60.