Dinocephalia

Dinocephalians are a group of therapsids that flourished for a brief time during the Middle Permian period, roughly 270-260 million years ago. They are part of the clade Therapsida which includes mammal-like reptiles and mammals.

Dinocephalians reached large sizes for their time, with some weighing as much as two tons.

Size
Dinocephalians include some very large forms, such as the 5-6 meter carnivore Anteosaurus or the 3-5 meter long herbivorous ''Jonkeria. However, most dinocephalians were in the 2-3 meter range, such as misleadingly named Titanosuchus''.

Classification
Dinocephalians include the estemmenosuchids, phreatosuchids, phthinosuchids and rhopalodontids along with the larger and more diverse clades Anteosauria and Tapinocephalia.

Extinction
Though dinocephalians diversified rapidly, they suddenly became extinct at the peak of their diversity around 260 million years ago. The cause of this extinction is uncertain, though climate change or competition by smaller therapsids because of environmental stress has been suggested.