Name:

Adelobasileus (Greek for "obscure king"); pronounced ADD-ell-oh-BASS-ih-LAY-us

Habitat:

Woodlands of North America

Historical Period:

Middle Triassic (225 million years ago)

Size and Weight:

About 5 inches long and a few ounces

Diet:

Insects

Distinguishing Characteristics:

Small size; mammal-like inner ears

 

About Adelobasileus:

Like many Mesozoic mammals, the mouse-sized Adelobasileus is known by frustratingly incomplete fossil remains: in this case, only a small portion of this wee creature's skull.


However, even this fragment is enough to establish that Adelobasileus possessed a very mammal-like inner-ear structure, which places it in the grey zone between the advanced therapsids (mammal-like reptiles) of the middle Triassic period and the first true mammals into which these creatures evolved. Some paleontologists even go so far as to identify Adelobasileus as the world's first mammal, though this conclusion would be on sounder footing with more extensive fossil evidence.