Hippopotamus Attack

The suggested subspecies were never widely used or validated by field biologists; the described morphological differences were small enough that they could have resulted from simple variation in non-representative samples. Genetic analyses have tested the existence of three of these putative subspecies. A study examining mitochondrial DNA from skin biopsies taken from 13 sampling locations, considered genetic diversity and structure among hippo populations across the continent. The authors found low but significant genetic differentiation among H. a. amphibius, H. a. capensis, and H. a. kiboko. Neither H.a.tschadensis nor H.a.constrictus have been tested.
Evolution
Until 1909, naturalists grouped hippos with pigs, based on molar patterns. Several lines of evidence, first from blood proteins, then from molecular systematics and DNA and the fossil record, show that their closest living relatives are cetaceans—whales, dolphins and porpoises. The common ancestor of hippos and whales branched off from Ruminantia and the rest of the even-toed ungulates; the cetacean and hippo lineages split soon afterwards.