With the dicynodonts, they form one of two lineages of therapsids that survived the End-Permian extinction and which diversified again during the Triassic, before the majority of them disappeared before or during the Triassic–Jurassic extinction, except for a lineage of cynodonts that later gave rise to mammals.
Classification
The clade was named in 1986 by James Allen Hopson and Herbert Richard Barghusen, the name meaning the "true Theriodontia". Within Hopson's system, the Eutheriodontia are the sister group of the Gorgonopsia within the Theriodontia.[1] A close relationship between therocephalians and cynodonts had been recognized for many years. In 2001 the Eutheriodontia were defined as the least inclusive clade including Mammalia and Bauria.[2] Even today, the taxon has a strong recognition among paleontologists and is regularly cited in several studies concerning therapsids.[3]
Evolutionary history and characteristics
The therocephalians and cynodonts are thought to have diverged in the Middle Permian, and each group independently evolved mammal-like features, including a secondary palate and the loss of a postorbital bar (these features were retained in mammals, which are considered a derived group of cynodonts). Mammalian features that both groups inherited from a common ancestor include the loss of teeth on the palate, the expansion of the epipterygoid bone at the base of the skull (an area called the alisphenoid in mammals), and the narrowing of the skull roof to a narrow sagittal crest running between large temporal openings.[4]
References
^Hopson J.A. and Barghusen H. 1986. "An analysis of therapsid relationships". pp. 83–106 in: Hotton N., MacLean P.D., Roth J.J., Roth E.C., eds. The Ecology and Biology of the Mammal-Like Reptiles. Washington, DC: Smithsonian Institution Press
^James A. Hopson and James W. Kitching, 2001, "A Probainognathian Cynodont from South Africa and the Phylogeny of Nonmammalian Cynodonts" pp 5-35 in: PARISH A. JENKINS, JR., MICHAEL D. SHAPIRO, AND TOMASZ OWERKOWICZ, EDITORS, STUDIES IN ORGANISMIC AND EVOLUTIONARY BIOLOGY IN HONOR OF A. W. CROMPTON Bullettin of the Museum of Comparative Zoology. Harvard University 156(1)
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