Fossil find 'may rewrite history'
(China Daily)
Updated: 2006-02-23 05:34

NANJING: With its front legs upright like a dog and hind legs stretching out like a lizard, experts say a newly discovered fossil may rewrite the history of mammalian evolution.

The two distinct bone characteristics in the fossil of a sharp-mouthed mammal were collected by Chen Piji, a Nanjing-based researcher of the Chinese Academy of Sciences (CAS), in the western part of Northeast China's Liaoning Province.

The British research journal, Nature, reported the unprecedented discovery, which is believed by some as holding the potential to change the traditional theory on the evolution of mammals.

Li Gang, the co-author of the paper alongside Chen, said existing mammals are classified into two groups viviparous therians, which have fully evolved bones, such as dogs, and oviparous monotremes, which have more primitive bones, such as lizards.

The newly discovered fossil, however, has the characteristics of both, a trait that has never been observed before, said Li, also a researcher with CAS Nanjing Institute of Geology and Palaeontology.

An analysis of the fossil shows the mammal, which lived some 120 million years ago in the early Cretaceous period, was about 12 centimetres long and weighed between 15 and 20 grams. It looks very much like a gecko, but with the help of a microscope, experts saw it had straight front legs, while its hind legs resemble those of a lizard, with a 90-degree angle between the thigh and calf.

Li guessed the mammal might have finished its evolution to become a therian, but its hind legs reverted into a more primitive form in order to survive in certain conditions.

(China Daily 02/23/2006 page3)