Whales and hippos are first cousins
24 January 2005, CIESM News

A group of four-footed mammals that flourished worldwide for 40 million years and then died out in the ice ages is the missing link between the whale and its not so obvious nearest relative, the hippopotamus. This new finding, published in the Proceedings of the National Academy of Sciences, puts an end to the long standing idea that the hippo is actually related to the pig or its close relative, the South American peccary.

Scientists from France, Chad and the United States found that whales and hippos had a common water-loving ancestor 50 to 60 million years ago that evolved and split into two groups: the early cetaceans, which eventually spurned land altogether and became totally aquatic; and a large and diverse group of four-legged beasts called anthracotheres. The pig-like anthracotheres -- at least 37 distinct genera -- existed over a 40-million-year period on all continents except Oceania and South America, then died out less than two and a half million years ago, leaving only one descendent: the hippopotamus.

Two hundred years ago the famous French paleontologist Georges Cuvier used fossil teeth to classify the relationship between hippos and pigs, however teeth comparisons turned out to be unreliable. All this changed in 1985 when an eminent scientist in the field of molecular evolution analyzed blood proteins and saw a close relationship between hippos and whales. A subsequent analysis of mitochondrial, nuclear and ribosomal DNA solidified this relationship. Also new whale fossils discovered in Pakistan in 2001, some of which have limb characteristics similar to artiodactyls, drew a more certain link between whales and artiodactyls. The team conducted a phylogenetic analysis of new and previous hippo, whale and anthracothere fossils and were able to persuasively argue that anthracotheres are the missing link. However researchers still disagree how they are related and where they belong within the even-toed ungulates, the artiodactyls.