Images of an Ancient Hippo Ancestor
The new discovery confirms a notion that had long been suspected based on genetic data, but could not be confirmed because the fossil record was so scarce.
Fabrice Lihoreau, a paleontologist at the University of Montpelier in France, and his colleagues, were studying the collections in a museum in Nairobi when they noticed a jaw that may have come from an anthrocothere, a family of primitive, hippo-like creatures that lived about 40 million years ago.
Intrigued, they decided to go to the area in Kenya where the jaw was found, a promontory known as Lokone Hill, with 28-milion-year-old rocks teeming with ancient aquatic creatures.
The team found several teeth that looked like they came from anthrocotheres. The molars, such as the one shown here, had a distinctive trifoliate pattern, or three-leafed pattern, that is commonly found in hippos. Because mammal teeth are so unique, this distinctive pattern revealed that the tooth came from an ancient ancestor to hippos. The team named the animal Epirigenys lokonensis, which roughly translates to "original hippo from Lokone."
Here, scientists show how the teeth of the ancient anthrocothere (on the upper left) evolved into those of the Epirigenys lokonensis (upper middle) and then into those of modern-day hippos (upper right). The cusps are shown as black circles in the diagrams below, while the crests are depicted with black lines and the enamel islets shown in orange.
The ancient creatures would have looked a bit like a shrunken, slender hippo and wouldn't have been much bigger than a sheep, weighing in at about 220 pounds (100 kg). While animals from the family of anthrocotheres have been found throughout the world, only the current find is a direct ancestor to hippos. Here, a depiction of an anthrocothere, though not the Epirigenys lokonensis.
Anthrocotheres are part of lineage from which hippos, whales and dolphins evolved. Even though the hippo's portly body may resemble that of the pig, it is more closely relatd to whales, who shared a common ancestor with hippos about 53 million years ago.
The new study also reveals that, since the ancestor to all hippos evolved in Africa, the hippos is a truly native species to the continent, unlike other animals found on safaris, such as lions and antelopes, which evolved in Asia.