The newly discovered dinosaur's hand is unusual and provides surprising new insights into a long-standing controversy over which fingers are present in living birds, which are theropod dinosaur descendants. The hands of theropod dinosaurs suggest that the outer two fingers were lost during the course of evolution and the inner three remained. Conversely, embryos of living birds suggest that birds have lost one finger from the outside and one from the inside of the hand. Unlike all other theropods, the hand of Limusaurus strongly reduced the first finger and increased the size of the second. Drs. Clark and Xu and their co-authors argue that Limusaurus' hand represents a transitional condition in which the inner finger was lost and the other fingers took on the shape of the fingers next to them. The three fingers of most advanced theropods are the second, third and fourth fingers--the same ones indicated by bird embryos--contrary to the traditional interpretation that they were the first, second and third.The article will appear in the June 18 issue of Nature.
Thursday, June 18, 2009
More on Limusaurus inextricabilis
InSciences has an expanded article on the discovery of the beaked dinosaur with the more avian-like hand structure: