Temporal range: Late Triassic, 225 Ma
Lucas & Hunt 1990
Adelobasileus cromptoni is a species of an extinct genus of mammal-like synapsid from the Late Triassic (Carnian), about 225 million years ago. It is known only from a partial skull recovered from the Tecovas formation in western Texas, southern United States.
Roughly contemporary with the mammaliaform Tikitherium, Adelobasileus predates the non-mammalian cynodonts Tritylodontidae and Tritheledontidae by 10 million years. In fact, distinct cranial features, especially the housing of the cochlea, suggest that Adelobasileus is a transitional form in the character transformation from cynodonts to Triassic mammals. For this reason, it is thought to be the common ancestor of all modern mammals or a close relative of the common ancestor. Though traditionally classified as a mammal by trait-based taxonomy, it is outside the crown group containing all true mammals.
- Lucas, SG; Hunt, AP (1990). "The oldest mammal". New Mexico Journal of Science. 30 (1): 41–49.
- Lucas, SG; Luo, Z (September 1993). "Adelobasileus from the upper Triassic of west Texas: the oldest mammal". J. Vert. Paleont. 13 (3): 309–334. doi:10.1080/02724634.1993.10011512.
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