Pleistocene Horse, Senile

Here's a set of lower cheek teeth from a senile Equus horse.

The common condition in ungulates (excepting some tapirs and hippos) is that the first premolar, upper and lower, is greatly reduced in size or is lost. What's left is a row of six "cheek teeth", P2-M3 for uppers (upper case lettering) and p2-m3 for lowers (lower case). The sequence goes like this: P2-P3-P4-M1-M2-M3, front to rear.

Other taxa have different teeth arrangements