Adelobasileus

Adelobasileus is an extinct proto-mammal from the Upper Triassic, about 225 million years ago. There is only a partial skull from strata in western Texas.
Skull features, like the housing of the cochlea, suggest that "Adelobasileus" is a transitional form in the evolution from cynodonts to end-Triassic mammals. For this reason, it may be close to modern mammals' common ancestor. Their sleek body type suggests they moved very fast.