Although now exclusively African, the family (of which all the representatives may be included in the single genus Hippopotamus, with several subgeneric groups) is represented in the Pliocene of Europe and the Lower Pliocene of northern India.
They are divided into several subgeneric groups.
It is true, as was pointed out by Sedgwick, that the species from the same part of the world resemble one another more closely than they do species from other regions, but recent researches have shown that the line between them cannot be so sharply drawn as was at first supposed, and it is certainly not desirable in the present state of our knowledge to divide them into generic or subgeneric groups, as has been done by some zoologists.
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