LOS ANGELES, Jan. 24 (Xinhuanet) -- The whale and the hippo, two animals look most unlike, are closest relatives with a common water-loving ancestor, scientists at the University of California,Berkeley, said Monday.

    In a paper appearing in the online edition of the journal Proceedings of the National Academy of Sciences, researchers overthrew the traditional concept that hippos were related to pigsor the peccaries, saying a group of four-footed mammals that flourished worldwide for 40 million years and then died out in theice ages is the missing link between the whale and the hippo.

    Whales don't look anything like hippos, because there is a 40-million-year gap between fossils of early cetaceans and early hippos, Jean-Renaud Boisserie, post-doctoral fellow at UC Berkeleywho led the research, said in the paper.

    Boisserie and colleagues filled in this gap by proposing 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, which blossomed over a 40-million-year period into at least 37 distinct genera on all continents except Oceania and South America, died out less than 2.5 million years ago, leaving only one descendent, the hippo.

    This proposal places whales squarely within the large group of even-toed ungulates, the group that includes cows, pigs, sheep, antelopes, camels, giraffes and most of the large land animals. Rather than separating whales from the rest of the mammals, the new study supports a 1997 proposal to place the legless whales anddolphins together with the cloven-hoofed mammals in a group.

    The origin of hippos has been debated for nearly 200 years eversince the animals were rediscovered. Earlier conclusion that hippos are closely related to pigs and peccaries was based primarily on their interpretation of the ridges on the molars of these species, Boisserie said.

    But in 1985, scientists found a much closer relationship between hippos and whales after analyzing blood proteins and othermolecular data of the two animals.

    Now most biologists agree that whales and hippos are first cousins, but they continue to clash over how whales and hippos arerelated, and where they belong within the even-toed ungulates, theartiodactyls. A major roadblock to linking whales with hippos was the lack of any fossils that appeared intermediate between the two.

    The latest analysis, according to Boisserie, finally brings thefossil evidence into accord with the molecular data, showing that whales and hippos indeed are one another's closest relatives,

    Boisserie and his colleagues conducted a phylogenetic analysis of new and previous hippo, whale and anthracothere fossils and were able to argue persuasively that anthracotheres are the missing link between hippos and cetaceans.

    While the common ancestor of cetaceans and anthracotheres probably wasn't fully aquatic, it likely lived around water, scientists said in the paper. And while many anthracotheres appearto have been adapted to life in water, all of the youngest fossilsof anthracotheres, hippos and cetaceans are aquatic or semi-aquatic.Enditem