Tiny deer-like mammals were whales ancestors

December 20th, 2007 - 1:22 pm ICT by admin  

Washington, December 20 (ANI): Whales have evolved from tiny deer-like mammals that jumped into rivers to flee prehistoric predators, according to a new study.

Lead researcher Hans Thewissen, a palaeontologist at North-eastern Ohio Universities Colleges of Medicine and Pharmacy, has revealed that the semi-aquatic creatures called Indohyus lived in southern Asia some 48 million years ago.

According to him, the raccoon-size mammals were part of a large group of mammals known as artiodactyls, which includes pigs, sheep, hippos, and giraffes.

Recent studies of fossils have suggested that whales evolved from artiodactyls, and that the hippopotamus is their closest living relative.

The new study, however, shows that hippos do not appear in the fossil record until about 35 million years after whales diverged from their land-dwelling ancestors, and thus there exists a gap in the evolutionary chain.

During the study, hundreds of Indohyus fossils found in mudstone in Kashmir were examined.

“We think that Indohyus was living there in little herds and that a whole bunch of these animals died. Their bones were then washed into this river and they were all buried together,” National Geographic quoted Thewissen as saying in a paper published in Nature magazine.

He says that the distinct features of the fossils drop a hint that the ancient hoofed mammals may be the long-sought “missing links” in the evolution of whales.

He particularly points at the structure of the animal’s skull and ears that suggest that Indohyus was closely related to whales.

Given that Indohyus looked like a deer, Thewissen says that his teams findings are “very surprising”.

“It was only the size of a raccoon, but if you saw it in a zoo, you would think it was a miniaturized deer,” he said.

The researchers say that Indohyus spent much of its time in the water, and that the ratios of chemical clues called isotopes in its teeth are characteristic of animals that ingest water while feeding.

Analysing the fossil teeth’s chemistry, the researchers came to the conclusion that found that the creature was an herbivore. This finding contrasts with the age-old thought that the earliest whales took to the water in pursuit of fish.

“Clearly, this is not the case. Indohyus is a plant-eater and already aquatic. Apparently the dietary shift to hunting animals (as modern whales do) came later than the habitat shift to water,” Thewissen said.

The study also proposes that Indohyus might have been drawn to water to escape land predators. The researcher say that the African mouse deer, a tropical forest dweller that feeds on land but flees into rivers when in danger, also shows a similar behaviour.

However, University of Michigan paleontologist Philip D. Gingerich feels that more convincing information is needed than is provided by Thewissens team. He says that the crucial piece of evidence that would link Indohyus to whales is a full analysis of the ear bone covering the animal’s middle ear.

“(Thewissen and colleagues) say one side is much thicker than the other, and that that’s a whale characteristic, which it is. But it’s so surprising to see that in an animal that otherwise looks completely terrestrial,” he said.

He further said that since the ear bone is “absolutely the key feature, I cannot understand why they wouldn’t show us some kind of cross-section, computerized tomography scan, or anything that would convince a person that they hadn’t just measured (a fossil ear bone) that was broken.” (ANI)

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