Dinocephalia
Extinct clade of stem-mammals
From Wikipedia, the free encyclopedia
Dinocephalia is a clade of generally large-bodied therapsids that flourished during Middle Permian between approximately 275 and 260 million years ago (Ma),[1][2][3] but became extinct during the Capitanian mass extinction event. Dinocephalians included herbivorous, carnivorous, and omnivorous forms.[4] Many species had thickened skulls with many knobs and bony projections. Dinocephalians were the first non-mammalian therapsids to be scientifically described[5] and their fossils are known from Russia, China, Brazil, South Africa, Zimbabwe, and Tanzania.[6][7]
| Dinocephalia | |
|---|---|
 | |
| Restoration of two genera of dinocephalians : Titanophoneus (an anteosaur) devouring a Ulemosaurus (a tapinocephalian). | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Suborder: | †Dinocephalia Seeley, 1894 |
| Subgroups | |
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See Taxonomy | |
Description
Dinocephalians retain a number of primitive characteristics (e.g. no secondary palate, small dentary) shared with their pelycosaur ancestors, although they are also more advanced in possessing therapsid adaptations like the expansion of the ilium and more erect limbs.
They include carnivorous, herbivorous, and omnivorous forms. It has been disputed as to whether some dinocephalians were semi-aquatic like hippopotamuses.[8]
Size
Dinocephalians were generally large in size,[1] and some the largest animals of the Permian period. The herbivorous or omnivorous Jonkeria has been suggested to have weighed 989 kilograms (2,180 lb), while the large carnivore Anteosaurus has been estimated to weigh 400 kilograms (880 lb) based on scaled 3D models.[9]
Skull
All dinocephalians are characterised by the interlocking incisor (front) teeth, though this was formerly thought to be unique to the group, it is also found in biarmosuchians.[10] Correlated features are the distinctly downturned facial region, a deep temporal region, and forwardly rotated suspensorium. Shearing contact between the upper and lower teeth (allowing food to be more easily sliced into small bits for digestion) is achieved through keeping a fixed quadrate and a hinge-like movement at the jaw articulation. The lower teeth are inclined forward, and occlusion is achieved by the interlocking of the incisors. The later dinocephalians improved on this system by developing heels on the lingual sides of the incisor teeth that met against one another to form a crushing surface when the jaws were shut.
Most dinocephalians also developed a thickened (pachyostotic) and ornamented skull roof, sometimes with horn-like projections, with the tapinocephalids suggested to have engaged in head-butting.[1] Other dinocephalians may have engaged in biting or head interlocking combat against rival individuals.[11]
Evolutionary history
Dinocephalians first appeared during the early Roadian as evidence by remains found in Russia, but their geographic origin and early evolution like that of other therapsids in general is not clear.[12][13]
| Phylogeny of Dinocephalia following Fraser-King et al. 2019[14] |
During the Wordian and early Capitanian, advanced dinocephalians radiated into a large number of herbivorous forms, representing a diverse megafauna. This is well known from the Tapinocephalus Assemblage Zone of the Southern African Karoo.
At the height of their diversity (middle or late Capitanian age) all the dinocephalians suddenly died out, during the Capitanian mass extinction event. The reason for their extinction is not clear; although disease, sudden climatic change, or other factors of environmental stress may have brought about their end. They were replaced by much smaller therapsids; herbivorous dicynodonts and carnivorous biarmosuchians, gorgonopsians and therocephalians.
Taxonomy
- Class Synapsida
- Order Therapsida
- Suborder Dinocephalia
- ?Driveria
- ?Mastersonia
- Family Estemmenosuchidae
- ?Family Phreatosuchidae
- ?Family Phthinosuchidae
- Family Rhopalodontidae
- Infraorder Anteosauria
- Family Anteosauridae
- Family Brithopodidae
- Family Deuterosauridae
- Infraorder Tapinocephalia
- ?Dimacrodon
- ?Driveria
- ?Mastersonia
- Family Styracocephalidae
- Family Tapinocephalidae
- Family Titanosuchidae
- Suborder Dinocephalia
- Order Therapsida