Artist’s impression of Xiaotingia zhengi.
Credit: Xing Lida and Liu Yi
Skeleton of Xiaotingia zhengi.
Credit: Xu et al. Nature
DUBLIN: A newly discovered fossil of an unknown species of bird-like dinosaur from China has raised questions over whether Archaeopteryx really is the earliest and most primitive bird.
Using the new fossil, Chinese scientists concluded that Archaeopteryx belongs not at the base of the bird evolutionary tree, but among the non-avian dinosaurs. If true, bird evolution will need to be re-examined.
"Our analysis suggests that Archaeopteryx is not a bird, but ancestral to Velociraptor, a dinosaur featured in the film Jurassic Park," said lead author Xing Xu from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences in Beijing of the paper published in Nature.
Missing link
Resembling a cross between a bird and a reptile, Archaeopteryx has been famous since its discovery in 1861. Its transitional features supported the ideas Charles Darwin had recently set out in his book On the Origin of Species.
Ten Archaeopteryx fossils have now been found and was long believed to be the earliest and most primitive bird.
But Xing and his colleagues say that Archaeopteryx-like fossils belong at the base of the Deinonychosauria - dinosaurs known for their switchblade-like claws. They write that this challenges the view that Archaeopteryx represents a pivotal group for understanding the transition from dinosaurs to birds.
By analysing how its features and those of other bird-like dinosaurs are related, the researchers compiled a phylogenetic tree to show which fossils are most closely related. The newly-discovered "Archaeopteryx-like theropod" from the Jehol beds in China is a new species of small, long-armed, four-winged dinosaur, said Xu, who named it Xiaotingia zhengi.
Knocked off its perch
The new research moves Archaeopteryx out of the birds, but not far.
"Birds are dinosaurs and our basic views on the origin of birds are unchanged by this new finding," said Lawrence Witmer of Ohio University in the U.S. who wrote an accompanying commentary in today's Nature. Archaeopteryx has just slid over from being a basal avian dinosaur to a basal non-avian dinosaur, he added: "Seems subtle, but it changes how we view the evolution of birds."
Just about all of our theories about the early evolution of birds have been based on Archaeopteryx being the oldest bird, so we need to have another look at everything, Witmer said. However, he added that the evidence for the move is "pretty good but not rock solid." The next new fossil find could shake things up again.
Other experts dispute the fall of Archaeopteryx. Luis Chiappe of the Dinosaur Institute, Natural History Museum of Los Angeles County is not convinced by the analysis or the conclusions. He believes it exaggerates the importance of the new fossil for understanding bird origins. "Archaeopteryx, by far the most anatomically informative fossil in the immediate transition towards birds, will continue to play a key role, whether it is interpreted as a bird or just immediately outside them," he said.
"Keep in mind that Archaeopteryx is known from 10 specimens that collectively provide a wealth of anatomical information, as opposed to a single, partially complete specimen of Xiaotingia, whose age is not even well established."
