(cohort Ferungulata, superorder Protoungulata)
An extinct order of ungulates that, apart from one lower Eocene representative from N. America and a well-established representative from the late Palaeocene of eastern Asia, are exclusively S. American. They flourished on that continent during the Oligocene and survived to the Pleistocene, evolving into many forms. Their dentition was complete and the tympanic bulla was large, the structure of the ear being different from all other mammals. They were mesaxonic, many of them possessing only three digits. Some had claws, but others appear to have possessed hoofs, though none achieved an unguligrade gait. Some later forms became large. Toxodon, which may have been the most common large ungulate during the S. American Pleistocene, was about 2.75 m long, had a massive head, and hind legs that were much longer than the fore legs. In life it may have looked like a very large guinea-pig. In addition there were the homalodotheres, which resembled the Chalicotheriidae (the so-called ‘clawed horses’), and a range of large and small rodent-like animals referred to as hypotheres.
Subjects: Zoology and Animal Sciences.