New evidence casts doubt on the theory that Sinosauropteryx possessed 'protofeathers'.
Credit: American Museum of Natural History
PARIS: Palaeontologists are in fierce debate over a fossil which provides the key evidence backing the theory that birds descended from dinosaurs.
The row focuses on Sinosauropteryx, a fossil found in 1994 by a farmer in Liaoning province, northeastern China, a treasure trove of the Early Cretaceous period some 130 million years ago.
About the size of a turkey, the long-tailed meat-eating dinosaur was covered with a down of fibres that Chinese researchers claimed were primitive feathers. That claim had the effect of a thunderclap.
Although the "feathers" were clearly not capable of flight, their existence dramatically supported a theory first aired in the 1970s: that birds evolved from dinosaurs. As a result, a notion once considered outlandish has become the mainstream concept for the origin of Aves, as birds are classified.
But a paper published this week in the British journal Proceedings of the Royal Society B, casts serious doubt on the protofeathers claim.
Feathers or frills?
According to Theagarten Lingham-Soliar of the University of KwaZulu-Natal in South Africa, who led the study, the two-branched structures called rachis that were proclaimed as early feathers are simply the remains of a frill of collagen fibres that ran down the dinosaur's back from head to tail.
The evidence comes from a recently discovered specimen of Sinoauropteryx – found in the same Yixian Formation at Liaoning – that Lingham-Soliar scrutinised under a high-powered microscope.
"The fibres show a striking similarity to the structure and levels of organisation of dermal collagen," the kind of tough elastic strands found on the skin of sharks and reptiles today, the researchers said.
The fibres have an unusual "beaded" structure, but this was most likely caused by a natural twisting of these strands, and a clumping together caused by dehydration when the dinosaur died and its tissues began to dry.
The tough fibres could have been either a form of armour that protected the small dinosaur from predators, or could have had a structural use, such as stiffening the animal's tail.
The early bird
The first known bird is Archaeopteryx, which lived around 150 million years ago. What is missing are the links between Archaeopteryx and other species that would show how it evolved. But the fossil record is frustratingly small and incomplete and this is why debate has been so fierce.
The birds-from-dinosaurs theory is based on the idea that small, specialised theropod dinosaurs - carnivorous, bipedal dinosaurs with three-toed feet - gained an advantage by developing plant-eating habits, growing feathers to keep warm and taking to the trees for safety. From there, it was a relatively small step to developing gliding skills and then the ability to fly.
Lingham-Soliar's team do not take issue with the theory itself. But they are dismayed by what they see as a reckless leap to the conclusion that Sinoauropeteryx had the all-important protofeathers, even though the this dinosaur was phylogenetically far removed from Archaeopteryx.
The evidence in support of the primitive feathers has not been thoroughly investigated, Lingham-Soliar said. "There is not a single close-up representation of the integumental structure alleged to be a protofeather," Lingham-Soliar said.
Given that the evolution of the feather is a pivotal moment in the history of life, "scientific rigour is called for," he said.
