''Adelobasileus'' is a genus of

mammaliamorph Mammaliamorpha is a clade of cynodonts. It contains the clades Tritylodontidae and Mammaliaformes, as well as a few genera that do not belong to either of these groups. The family Tritheledontidae has also been placed in Mammaliamorpha by some ...

cynodonts from the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

(

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...

), about 225 million years ago. It is known only from a partial skull recovered from the

Tecovas Formation The Tecovas Formation is a geological formation in Texas.Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Triassic, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berk ...

in western

Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...

, southern United States, referred to the species ''Adelobasileus cromptoni''. Roughly contemporary with the

mammaliaform Mammaliaformes ("mammalian forms") is a clade that contains the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts. It is defined as the clade originating from the most recent comm ...

'' Tikitherium'', ''Adelobasileus'' predates the non-mammalian cynodonts Tritylodontidae and

Tritheledontidae Tritheledontidae, the tritheledontids or ictidosaurs, is an extinct family of small to medium-sized (about 10 to 20 cm long) cynodonts. They were highly mammal-like, specialized cynodonts, although they still retained a few reptile-like ana ...

by 10 million years. Distinct cranial features, especially the housing of the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory or ...

, suggest that ''Adelobasileus'' is a

transitional form A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross a ...

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 Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...

of all modern mammals. Though traditionally classified as a mammal by trait-based taxonomy, it is outside the crown group containing all true mammals.

References

Sources

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External links

Adelobasileus from Palaeos
Prehistoric prozostrodonts Prehistoric cynodont genera Late Triassic synapsids Triassic synapsids of North America Fossil taxa described in 1990 Taxa named by Spencer G. Lucas Taxa named by Adrian P. Hunt {{Triassic-animal-stub