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. The term pachyderm is commonly used to describe elephants, rhinoceroses, hippopotamuses and tapirs. The grouping was determined to be artificial as a biological classification due to genetic studies.