On the origins of Hippopotamidae togetherwith descriptions of two new species, a new genus and a new subfamily from the Miocene of Kenya

The discovery of Kenyapotamus coryndoni and K. ternani, two new taxa of Hippopotamidae, permits a reassessment of the origins of the family. Hitherto considered to have been derived from an anthracothere stock, it now seems more likely that Hippopotamidae evolved from Old World Tayassuidae early in the middle Miocene or in the lower Miocene. The new genus is known by two species, a small one at Fort Ternan and Maboko, a slightly larger one at Ngeringerowa and Nakali. The palaeoenvironments of large amphibious mammals of Eastern Africa are examined. It is noted that Anthracotheres which were common in lower Miocene deposits of Kenya became extinct locally by the time that the earliest hippopotamids came on the scene. A straightforward niche exchange may be visualised whereby hippopotamids either replaced anthracotheres in the East African large mammal amphibious niche, or evolved in response to the vacation of this niche by anthracotheres. The earliest true Hippopotamus appears in the Kenya fossil record rather abruptly at about 7 m.y. ago. So far the new genus and Hippopotamus have not been found together in the same deposits. © 1983.