Webster's Revised Unabridged Dictionary
Cf. F. solipède, It. solipede, Sp. solipedo,; apparently fr. L. solus, alone + pes, pedis, a foot; but probably fr. L. solidipes, solid-footed, whole-hoofed. See Solid, and Pedal
Chambers's Twentieth Century Dictionary
L. solus, alone, pes, pedis, a foot.
They are peculiar to solipeds.
"Special Report on Diseases of the Horse" by United States Department of Agriculture
The bones of the tarsus are not seven in all animals; they are fewer in ruminants and solipeds.
"Artistic Anatomy of Animals" by Édouard Cuyer