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Temporal range: Lower PermianLower Cretaceous (non-mammalian)
Inostrancevia skull.JPG
Inostrancevia, a therapsid
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Eupelycosauria
Clade: Haptodontiformes
Clade: Sphenacomorpha
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Clade: Therapsida
Broom 1905

Therapsids, previously known as the mammal-like reptiles,[1] are an order of synapsids.

The clade includes the mammals, which are descended from the cynodont therapsids.

Characteristics[change | change source]

The jaws of therapsids had frontal incisors for nipping, large lateral canines for puncturing and tearing, and molars for shearing and tearing, and molars for shearing and chopping food.

Therapsid legs were positioned more vertically beneath their bodies than were the sprawling legs of Sauropsids and Pelycosaurs.

Evolution[change | change source]

The therapsids were seriously affected by the P/Tr extinction event. The successful gorgonopsians died out, and the remaining groups were much reduced.

The dicynodonts, now represented by a single family of large stocky herbivores, the Kannemeyeridae, and the medium-sized cynodonts (including both carnivorous and herbivorous forms), flourished worldwide, throughout the early to middle Triassic. They died out across much of Pangea before the end of the Upper Triassic, although they continued for some time longer in the wet equatorial band and the south.

At least three groups of eucynodonts survived. They appeared in the Upper Triassic. The extremely mammal-like family, the Tritylodonts, survived into the Lower Cretaceous. Another group, Morganucodon and similar animals, were mammaliaformes or the "stem-mammals" for the mammals.

Taxonomy[change | change source]

References[change | change source]

  1. They are not reptiles.
  • Kemp T.S. 2005. The origin and evolution of mammals. Oxford University Press
  • Benton M.J. 2004. Vertebrate Paleontology. 3rd ed. Blackwell, Oxford.
  • Carroll R.L. 1988 Vertebrate Paleontology & Evolution. Freeman N.Y.
  • Romer A.S. 1966. Vertebrate Paleontology. 3rd ed, University of Chicago Press.