Source : Webster's Revised Unabridged Dictionary (1913)

Pachydermata \Pach`y*der"ma*ta\, n. pl. [NL., fr. Gr. ?
   thick-skinned; pachy`s thick + ? skin.] (Zo["o]l.)
   A group of hoofed mammals distinguished for the thickness of
   their skins, including the elephant, hippopotamus,
   rhinoceros, tapir, horse, and hog. It is now considered an
   artificial group.