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

English

Noun

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

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

• Class Synapsida
• ORDER THERAPSIDA *
  • Suborder Biarmosuchia *
    • Family Biarmosuchidae
      • Biarmosuchus
    • Family Eotitanosuchidae
      • Eotitanosuchus
  • Eutherapsida
    • Suborder Dinocephalia
      • Family Estemmenosuchidae
        • Estemmenosuchus
      • Anteosauria
        • Family Syodontidae
        • Family Brithopodidae
        • Family Anteosauridae
      • Tapinocephalia
        • Family Titanosuchidae
        • Family Tapinocephalidae
    • Neotherapsida
      • Suborder Anomodontia *
        • Superfamily Venyukoviamorpha
          • Family Venyukoviidae
            • ''Suminia
        • Infraorder Dicynodonta
      • Theriodontia *
        • Suborder Gorgonopsia
          • Family Gorgonopsidae
        • Eutheriodontia
          • Suborder Therocephalia
          • Suborder Cynodontia *
            • (unranked) Mammaliformes *
• Class Mammalia

Phylogeny

Synapsida | Sphenacodontia |-Sphenacodontidae `-Therapsida |-?Tetraceratops `-+-Biarmosuchia | |-Eotitanosuchidae | `-?Phthinosuchidae `-Eutherapsida |-Dinocephalia | |-Anteosauria | `-Tapinocephalia `-Neotherapsida |-Anomodontia | |-Dromasauria | `-Dicynodontia `-Theriodontia |-Gorgonopsia | |-Lycaenops | `-Inostrancevia `-Eutheriodontia |-Therocephalia | `-Eutherocephalia | `-Bauria'' `-Cynodontia `-Mammalia

See also

• Vertebrate paleontology
• Evolution of mammals
• Timeline of evolution

External links

• "Therapsida: Mammals and extinct relatives" Tree of Life
• "Therapsida: overview" Palaeos
• "Therapsids in Detail". Stephen Priestley - Illustrator

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.