Pachydermata

A hippopotamus (Hippopotamus amphibius)

An Indian rhinoceros (Rhinoceros unicornis)

Pachydermata (meaning 'thick skin', from the Greek παχύς, pachys, 'thick', and δέρμα, derma, 'skin') is an obsolete order of mammals described by Gottlieb Storr, Georges Cuvier, and others, at one time recognized by many systematists. Because it is polyphyletic, the order is no longer in use,^[when?] but it is important in the history of systematics. Outside strict biological classification, the term "pachyderm" is commonly used to describe elephants, rhinoceroses, hippopotamuses and tapirs.