dicynodont n : a kind of therapsid

The Dicynodontia are a taxon of Therapsids or mammal-like reptiles. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means 'two dog tooth'. They are also the most successful and diverse of the therapsids, with over 70 genera known, varying from rat- to ox-sized.

Characteristics

Dicynodonts first appear during Middle Permian, and underwent a rapid evolutionary radiation, becoming the most successful and abundant land vertebrates of the Late Permian. During this time they including a large variety of ecotypes, including large, medium-sized, and small herbivores and short-limbed mole-like burrowers.

Only two families survived the end Permian extinction, one of which, the Lystrosauridae, were the most common and widespread herbivores of the Induan (earliest Triassic). These medium-sized animals evolved into and were replaced by the Kannemeyeridae, stocky, pig- to ox-sized animals that were the most abundant herbivores worldwide from the Olenekian to the Ladinian age. By the Carnian they had been supplanted by Traversodont cynodonts and rhynchosaur reptiles. During the Norian (middle of the Late Triassic), when - perhaps due to increasing aridity - they drastically declined, and the role of large herbivore was taken over by sauropodomorph dinosaurs.

With the decline and extinction of the Kannemeyerids, there were to be no more dominant large synapsid herbivores until the middle Paleocene epoch (60 Ma) when mammals, descendants of cynodonts, began to diversify after the extinction of the dinosaurs.

It used to be thought that Dicynodonts died out completely before the end of the Triassic. Recently however, evidence has come to light showing the dicynodonts survived into the Cretaceous in southern Gondwana (now Queensland) (Thulborn and Turnmer, 2003).

Systematics

Taxonomy

• • Superfamily Kingorioidea
    • Family Kingoriidae
  • Clade Diictodontia
    • Superfamily Emydopoidea
      • Family Cistecephalidae
      • Family Emydopidae
    • Superfamily Robertoidea
      • Family Diictodontidae
      • Family Robertiidae
  • Clade Pristerodontia
    • Genus Dinanomodon
    • Genus Odontocyclops
    • Genus Propelanomodon
    • Family Aulacocephalodontidae
    • Family Dicynodontidae
    • Family Kannemeyeriidae
    • Family Lystrosauridae
    • Family Oudenodontidae
    • Family Pristerodontidae
    • Family Shanisiodontidae
    • Family Stahleckeriidae

Phylogeny

The cladogram presented here follows a synthesis from Mikko's Phylogeny Archive.

See also

• Dicynodon
• Dromasauria
• Evolution of mammals

References

• Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.
• Colbert, E. H., (1969), Evolution of the Vertebrates, John Wiley & Sons Inc (2nd ed.)
• Cox, B., Savage, R.J.G., Gardiner, B., Harrison, C. and Palmer, D. (1988) The Marshall illustrated encyclopedia of dinosaurs & prehistoric animals, 2nd Edition, Marshall Publishing
• Crompton, A. W, and Hotton, N. 1967. Functional morphology of the masticatory apparatus of two dicynodonts (Reptilia, Therapsida). Postilla, 109:1–51.
• King, Gillian M., "Anomodontia" Part 17 C, Encyclopedia of Paleoherpetology, Gutsav Fischer Verlag, Stuttgart and New York, 1988
• -- -- , 1990, the Dicynodonts: A Study in Palaeobiology, Chapman and Hall, London and New York
• Thulborn, Tony and Turner, Susan, 2003, "The last dicynodont: an Australian Cretaceous relict" Proceedings: Biological Sciences Vol 270, No 1518 / May 7, 2003; pp 985 - 993

External links

• Therapsida : Neotherapsida : Dicynodontia - Palaeos