Adelobasileus cromptoni
First mammal
Pronunciation: uh-DELL-oh-ba-sill-ee-us KROMP-ton-eye
Meaning: From Greek adelos, "obscure" and basiliskos, "king."
Size: 4.7 inches/.12 meters long
Diet: Meat Eater
Age: Late Triassic (225 million years ago)
Specimen Number: NMMNH P-12971
Location: Crosby County, Texas
Image By: David Baccadutre
Date: Spring 2008

This is the skull of the oldest known mammal, Adelobasileus, a tiny mouse-sized inhabitant of the Late Triassic forests. Discovered by NMMNHS paleontologists in 1989, the skeletal structure of the ear region identifies the skull as mammalian. Adelobasileus first evolved during the Triassic.

See a reconstruction of Adelobasileus here.