Friday, October 9, 2009

Clue to ear's evolution

WASHINGTON - RESEARCHERS digging in north-eastern China say they have discovered the fossil of a previously unknown chipmunk-sized mammal that could help explain how human hearing evolved.

Paleontologists unearthed the 123-million-year-old creature, which is just 15cm long, in fossil-rich Liaoning Province, near the Chinese border with North Korea.

What is most surprising, and thus scientifically interesting, is the animal's inner ear,' said Zhe-Xi Luo, a curator at the Carnegie Museum of Natural History in Pittsburgh and one of the study's authors. The condition of the 'remarkably well preserved' three dimensional fossil has allowed an international team of researchers to reconstruct how the creature's middle ear was connected to its jaw.

The find could be the link that explains how the three bones of the mammalian middle ear became separated from the jaw hinge - where the reptilian ear is found - to form a complex and highly-performing hearing system. 'Mammals have highly sensitive hearing, far better than the hearing capacity of all other vertebrates, and hearing is fundamental to the mammalian way of life,' said Mr Luo.

The development of the ear is seen as key to understanding survival techniques that steered mammals, including human ancestors, through the dinosaur-infested mesozoic period around 250 to 66 million years ago. 'The mammalian ear evolution is important for understanding the origins of key mammalian adaptations,' he said.

But there are still doubts where the creature, Maotherim asiaticus, fits in the evolutionary chain, and the novel ear connection could simply be a adaptation caused by changes in development, rather than an evolutionary link. The report is published in the Oct 9 issue of the journal Science. -- AFP

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