Adelobasileus predates and descends from the non-mammalian cynodonts Tritylodontidae and Tritheledontidae by 10 million years. Distinct cranial features, especially the housing of the cochlea, suggest that Adelobasileus is a transitional form in the character transformation from non-mammaliaform cynodonts to mammaliaforms. For this reason, it is thought to be a close relative of the common ancestor of all modern mammals. Though formerly classified as a mammal by trait-based taxonomy, it is outside the crown group containing all true mammals.[1]
Lucas, SG; Luo, Z (September 1993). "Adelobasileus from the upper Triassic of west Texas and central Arizona: the oldest mammal". J. Vertebr. Paleontol. 13 (3): 309–334. doi:10.1080/02724634.1993.10011512.
