The Collaborative International Dictionary of English v.0.48:

Pachydermata \Pach`y*der"ma*ta\
   (p[a^]k`[i^]*d[~e]r"m[.a]*t[.a]), n. pl. [NL., fr. Gr.
   pachy`dermos thick-skinned; pachy`s thick + de`rma skin.]
   (Zool.)
   A group of hoofed mammals distinguished for the thickness of
   their skins, including the elephant, hippopotamus,
   rhinoceros, tapir, horse, and hog; the pachyderms. It is now
   considered an artificial group.
   [1913 Webster]