Athena Review Image Archive ™
Adelobasileus cromptoni skull
Skull of Adelobasileus cromptoni (after Spencer and Luo 1993)
Adelobasileus cromptoni was a small stem mammal found in Crosby County, Texas in strata from the Dockum Formation, dating from the Late Carnian stage of the Triassic (225 mya). Fossils of a partial skull about 1.7 cm long, and teeth were discovered by Lucas and Hunt (1990).
While the lower, rear part of the skull (basicranium) shares numerous traits with early Jurassic mammals, other cranial features such as the petrosal region, which has only a small or incipient promontorium housing the ear cochlea, indicate only an intermediate stage of the character transformation from non-mammalian cynodonts to mammals. If they are mammalian, the Adelobasileus fossils would be at least ten million years older than than those of any previously described mammal (Lucas and Luo 1993).
References:
Spencer and Luo 1993
Spencer and Lucas 1990
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