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 suids (pigs and peccaries). Scientists earlier thought the hippo descended from another, now extinct, group.
This discovery, they say, bridges a gap in the fossil record. It officially separates these giants from the cetaceans – their closest modern-day cousins including whales, dolphins and porpoises.
All this is courtesy of a half-jaw and several teeth discovered at Lokone in the Lake Turkana basin in Kenya. The spectacular find now leads the scientific community to conclude that this was a new fossil species. It belongs to an equally new genus dating back to about 28 million years.
They named it Epirigenys lokonensis. The name is derived from two Turkana names – ‘Epiri’ which means hippo and ‘Lokone’, the site of the fossil discovery.
For a long time, palaeontologists 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. The secret of the hippo’s ancestry, therefore, remained a mystery until now.
Grooves in the teeth of the fossil (E. lokonensis) have similar patterns to those of anthracotheres. Anthracotheriidae are extinct relatives of hippos and whales. They 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 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.