Rodhocetus, a whale that lived 47 million years ago is based on new Eocene fossils from Pakistan. The ankle bones indicate a close relationship of early whales to land mammals such as hippopotami and pigs. FOTO – REUTERS
How whales evolved and who their ancestors were has been hotly debated for decades.
Scientists knew they were related to land mammals but the fossil evidence of the whale‘s 10-million-year transition from land to water has been sketchy.
Paleontologists have discovered 50-million-year-old fossils of early whales that lived on land, and ankle and skull bones from primitive aquatic whales that fill in the gaps.
„With these new discoveries the whale fossil record is now so complete,‘‘ Hans Thewissen, of Northeastern Ohio Universities College of Medicine, said.
„It shows us so well how whales became aquatic that it is probably the best, or one of the best, examples of evolution where these major changes are documented with fossils,‘‘ he added in a telephone interview.
Thewissen and his colleagues uncovered fossils of a fox-size mammal called Ichthyolestes, and Pakicetus which resembled a wolf .
The ankle bones are seen only in a group of animals known as artiodactyls such as cows, pigs and hippos. But the heads of the creatures have whale-like features. „They are whales that were still living on land. Their relatives are a group of even-toed ungulates,‘‘ Thewissen said, using another term for artiodactyls.
In a separate report in the journal Science, Professor Philip Gingerich, of the University of Michigan in Ann Arbor described a skeleton of a later aquatic whale that included both ankle and skull bones that he and his colleagues discovered in a different part of Pakistan.
The ankle bone was also of an artiodactyl.
„Now I even admit the possibility that hippos are a side line of artiodactyls that might be closer to the whales than any other living animals,‘‘ Gingerich said in a statement.
Until now paleontologists thought whales had evolved from mesonychians, an extinct group of land-dwelling carnivores, while molecular scientists studying DNA were convinced they descended from artiodactyls.
„The paleontologists, and I am one of them, were wrong,‘‘ Gingerich said.
Christian de Muizon of the Museum of Natural History in Paris described the discovery of the land whales as one of the most important events in the past century of vertebrate paleontology.
„The newly discovered fossils show the first whales were fully terrestrial, and were even efficient runners,‘‘ he said in a commentary in Nature. Reuters
