AskDefine | Define therapsid

Dictionary Definition

therapsid n : probably warm-blooded; considered direct ancestor of mammals [syn: protomammal]

User Contributed Dictionary

English

Noun

  1. Any extinct reptile, of the order Therapsida; thought to be direct ancestors of the mammals

Extensive Definition

Therapsids are an order of synapsids (Class Synapsida). Traditionally, synapsids were referred to as reptiles and were known as the "mammal-like reptiles". However, they are now classified as a sister-group to the reptiles, and are phylogenetically closer to the mammals. Indeed, when the term is used cladistically, the taxon also includes the mammals, which are descended from the cynodont therapsids. All other lineages of the therapsids are extinct; the last known survivors of the non-mammalian therapsids lived in the Early Cretaceous period.

Characteristics

Therapsids' temporal fenestrae were larger than those of the pelycosaurs. The jaws of therapsids were more complex and powerful and the teeth were differentiated into frontal incisors for nipping, large lateral canines for puncturing and tearing, and molars for shearing and chopping food. Therapsids' legs were positioned more vertically beneath their bodies than were the sprawling legs of reptiles and pelycosaurs.

Evolutionary history

see also Evolution of mammals

External links

References

  • Benton, M.J. (2004). Vertebrate Paleontology. 3rd ed. Blackwell Science Ltd
  • Carroll, R.L. (1988). Vertebrate Paleontology & Evolution. W.H. Freeman & Company, NY
  • Kemp, T.S. (2005). The origin and evolution of mammals. Oxford University Press
  • Romer, A.S. (1966). Vertebrate Paleontology. University of Chicago Press, 1933; 3rd ed.
therapsid in Catalan: Teràpsid
therapsid in German: Therapsiden
therapsid in Spanish: Therapsida
therapsid in French: Therapsida
therapsid in Galician: Therapsida
therapsid in Italian: Therapsida
therapsid in Hebrew: תראפסידה
therapsid in Hungarian: Therapsida
therapsid in Dutch: Therapsida
therapsid in Japanese: 獣弓類
therapsid in Norwegian: Therapsider
therapsid in Polish: Terapsydy
therapsid in Portuguese: Therapsida
therapsid in Russian: Терапсиды
therapsid in Simple English: Therapsida
therapsid in Slovak: Therapsida
therapsid in Finnish: Terapsidit
therapsid in Chinese: 獸孔目
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