Bird wings clearly share ancestry with dinosaur "hands" or forelimbs. A school kid can see it in the bones. But paleontologists have long struggled to explain the so-called digit dilemma.
Here's the problem: The most primitive dinosaurs in the famous theropod group (that later included Tyrannosaurus rex) had five "fingers." Later theropods had three, just like the birds that evolved from them. But which digits? The theropod and bird digits failed to match up if you number the digits from 1 to 5 starting with the thumb. Theropods looked like they had digits 1, 2 and 3, while birds have digits 2, 3 and 4.
That mismatch failed to support the widely accepted evolutionary link between dinosaurs and birds.
Now, newly described fossilized hands from a beaked, plant-eating dinosaur, called Limusaurus inextricabilis, reveal a transitional step in the evolution of modern wings from dino digits. The finding could resolve a debate over which fingers ultimately became embedded in the wing.
"Limusaurus is another one of those discoveries that makes one excited to be a paleontologist," said Matthew Lamanna of the Carnegie Museum of Natural History in Pittsburgh, who was not involved in the new study. "The discovery of a toothless, plant-eating Jurassic ceratosaur, from Asia of all places, is something that nobody in our field ever expected."
The remains of the dinosaur were discovered in the Junggar Basin of Xinjiang, in northwestern China. The deposits date back some 159 million years.
"This new animal is fascinating in and of itself, and when placed into an evolutionary context it offers intriguing evidence about how the hand of birds evolved," said James Clark of George Washington University. He and several colleagues have described the theropod dinosaur in the June 18 issue of the journal Nature.
Jack Conrad, vertebrate paleontologist at the American Museum of Natural History in New York, calls the finding a "spectacular discovery." Conrad was not involved in this current research.