The analysis of a new fossil ancestor of the modern hippo revealed secrets of the species' evolution.

In the past, researchers thought hippos were related to pigs, but this new work shows that hippos are not a part of the Suidae family, but instead descended from a group that has long been extinct. DNA analyses have also shown the hippo is actually more closely related to whales and dolphins (cetaceans) than pigs and peccaries.

The finding fills in a gap in the fossil record that had separated hippos from their closest cetacean ancestors still alive today, according to a news release. The revealing research also shows hippos colonized Africa long before other large mammals, as far back as 35 million years ago.

"The new fossils studied have made it possible to build the first evolutionary scenario that is compatible with both genetic and paleontological data," the researchers stated.

To make their findings, the researchers analyzed ancient bones and teeth found in Kenya, allowing them to describe a new 28-million-year-old related species, dubbed Epirigenys lokonensis. The characteristics of these fossils were compared with those of "ruminants, suoids, hippos and fossil anthracotheres (an extinct family of ungulates)" to show cetaceans are the hippos' closest living relatives.

The findings not only fill in 75 percent of the time gap separating hippos, but also completely change what we know about the history of the African animal kingdom. Africa was believed to have been an isolated continent between 18 million and 110 million years ago, and most of the animals seen there today are believed to have only arrived less than 20 million years ago. Researchers have always thought the same was true for hippos, but these new findings suggest their anthracothere ancestors may have moved over from Asia as far back as 35 million years ago.

The findings were published in a recent edition of the journal Nature Communications.