Merycoidodon skull and endocast

Merycoidon skull and endocast (Merycoidon culbertsoni)

Merycoidodontidae were extinct mammals related to camels, sheep and pigs. They roamed woodlands and grasslands of North America from about 34 million years ago to 5 million years ago. They were grazers, and because their fossil remains are found in large numbers in small areas, they probably lived in herds.

This specimen was collected in Wyoming in 1931. It is unusual because the jaw and skull are complete and articulated. Preservation with the mouth open is rare as well.
An endocast is a fossil mold of the brain, not the brain itself. The natural mold, made of sediment that washed into the cavity after the brain was gone, fossilized with the skull but eventually the skull was exposed and eroded away leaving the harder endocast. This specimen is not the same individual as the skull but is from the same family of animal.