The Surprising Story of Europe’s Hippos

Hippopotamuses are the largest land animals living today after elephants and rhinoceroses. Today, the species occurs only in Africa, but remains have also been found in Europe.

They have been assumed to originate from the last interglacial period. This assumption is based on the fact that the hippopotamus is considered an indicator species of temperate climates and is thought to have gone extinct north of the Mediterranean at the onset of the Weichselian glaciation around 115,000 years ago.

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A recent study by Patrik Arnold and his colleagues has now brought surprising new insights concerning European hippopotamuses. The researchers analyzed Central European hippopotamuses by sequencing the genome of one individual, which revealed a close genetic relationship between these animals and modern African hippopotamuses.

In addition, they determined six other partial mitochondrial genomes, which confirmed that the European fossils belonged to the same species as present-day African hippopotamuses. The species therefore once had a much wider distribution than today and was not always restricted to sub-Saharan Africa.

The researchers also conducted radiocarbon dating of the fossils and were greatly surprised to discover that they were much more recent than previously believed. The remains dated to the middle phase of the Weichselian glaciation, a period beginning before 47,000 years ago and ending around 31,000 years ago—that is, during the later stages of the last Ice Age.

Because radiocarbon dates of woolly mammoth and woolly rhinoceros fossils from the same sites fall within the same time range, these animals also inhabited Europe at that time. Consequently, the fauna of our continent was very different from what had previously been assumed or from what we know today.

The researchers also analyzed genetic variation in the now fully sequenced hippopotamus genome and found its genetic diversity to be low. It is therefore likely that this individual belonged to a small population that lived in isolation from other hippopotamuses.

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