June 17, 2009

New Beaked Dino Sheds Light on Evolution of Birds’ Fingers

Scientists have uncovered a beaked dinosaur in China that is providing new clues into how birds' hands evolved to develop fingers.

Writing in the journal Nature, scientist James Clark of George Washington University and Xu Xing of the Chinese Academy of Science's Institute of Vertebrate Paleontology and Paleoanthropology in Beijing detailed the new discovery, which was found amidst 159-million-year-old deposits in the Junggar Basin of Xinjiang.

"This finding is truly exciting, as it changes what we thought we knew about the dinosaur hand," said Xu. "It also brings conciliation between the data from million-year-old bones and molecules of living birds."

The team has named it Limusaurus inextricabilis, or "mire lizard who could not escape". They noted that the dinosaur is the first known herbivore theropod to be discovered with a beak. The fossil shows that the animal's jaw was toothless. Limusaurus carried short arms, but lacked sharp claws. Previously discovered creatures of that family were carnivores.

But more importantly, scientists noted characteristics about Limusaurus' hand that could answer long disputed questions over the evolution of birds' hands.

"This new animal is fascinating, and when placed into an evolutionary context it offers intriguing evidence about how the hand of birds evolved," said Clark.

Modern-day birds are living ancestors of theropod dinosaurs. Scientists have theorized that the outer two fingers were lost during evolution, causing the other three to remain.

However, upon analysis of embryos of living birds, scientists have found evidence to suggest that birds have lost one finger from the outside and one from the inside of the hand.

Xu and Clark said that Limusaurus' hand shows the loss of the inner finger, which resulted in surrounding fingers to take on the shape of those next to them.

"The transition to tetanurans involved complex changes in the hand including a shift in digit identities, with ceratosaurs displaying an intermediate condition," said Xu.

"This work on dinosaurs provides a whole new perspective on the evolution of bird manual digits," said H. Richard Lane, program director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research.

Scientists have previously found other dinosaur skeletons in the fossil beds of the Junggar Basin, including the oldest tyrannosaur, the oldest horned dinosaur and a new stegosaur.


Image Caption 1:This image shows a reconstruction of Limusaurus; there is no evidence of feather structures.
Credit: Portia Sloan


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