''Adelobasileus'' is a genus of mammaliamorph cynodonts from the

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

(

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followe ...

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

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

, 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 ...

Tikitherium ''Tikitherium'' is an extinct genus of mammaliaforms from the Late Triassic. It is thought to be an insectivore and a close relative to Docodonta. ''Tikitherium'' refers to Tiki, the village located near the Tiki Formation where the specimen was ...

'', ''Adelobasileus'' predates the non-mammalian cynodonts

Tritylodontidae Tritylodontidae ("three-knob teeth", named after the shape of their cheek teeth) is an extinct family of small to medium-sized, highly specialized mammal-like cynodonts, bearing several mammalian traits like erect limbs, endothermy and details o ...

and Tritheledontidae 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 org ...

, 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 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 In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

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