A team of French and Kenyan researchers has finally solved an old hippo mystery. They have revealed that these fascinating ancient creatures are not related to suoids (pigs and peccaries) as earlier thought but instead descend from another, now extinct, group.

This discovery, they say, bridges a gap in the fossil record separating these animals from their closest modern-day cousins, the cetaceans who include whales, dolphins and porpoises.

They have been analysing a half-jaw and several teeth discovered at Lokone in the Lake Turkana basin in Kenya which has led them to conclude that this was a new fossil species belonging to an equally new genus dating back to about 28 million years.

They named it Epirigenys lokonensis. The name is derived from 2 Turkana names – ‘Epiri’ which means hippo and ‘Lokone’, the site of the fossil discovery.

For long, paleontologists have thought these semi-aquatic animals, with their unusual morphology, were related to the Suidae family. DNA comparisons performed in the 1990s and 2000s revealed that the hippo’s closest living relatives were actually the cetaceans.

This discovery seemed to contradict most paleontological interpretations. The additional lack of fossil evidence did not make things any better and the secret of the hippo’s ancestry remained a mystery until now.

Grooves in the teeth of the fossil (E. lokonensis) have similar patterns to those of anthracotheres, a family of extinct relatives of hippos and whales that lived about 40 million years ago in what is now South East Asia.

But the enamel on E. lokonensis’ teeth is thicker and the points are blunter. The shape of the premolars is also more similar to that of hippo relatives that roamed Uganda about 21 million years ago.

This new information extracted from the teeth of E. lokonensis’ is helping the team close in on how hippos got to Africa. Back then Africa was an isolated continent, separated from other landmasses from nearly 110 million to 18 million years ago.

About 35 million years ago, small groups of primates and anthracotheres migrated from Asia to Africa. More species of mammals migrated again later, around 20 million to 18 million years ago, when a land bridge connected Asia and Africa.

The presence of E. lokonensis in Africa 28 million years ago can only mean that hippos might be descendants of the first wave of anthracotheres (earliest large terrestrial mammals) to invade Africa.

Since these anthracotheres needed to be able to swim to come to Africa, they may have developed their semi-aquatic lifestyle quite early. Finding out when this skill evolved in anthracotheres could help scientists reconstruct the common ancestor between hippos and their closest living relatives.

Since you know how the hippo came to Africa, go see them at Lake Naivasha.