Evolutionary Origins of Birds Precede Archaeopteryx, Study Suggests

Archaeopteryx, the Late Jurassic-era bird genus considered to be a key transitional species in the evolution of dinosaurs to birds, was preceded by a series of flying dinosaurs that simultaneously evolved to be smaller in size and have longer arms to support their feathered wings, according to a new evolutionary analysis.

Writing in the journal Evolution, University of Bristol Earth scientist Mark Puttick and his colleagues report their analysis of the rate of evolution in body size and forelimb length - two evolutionary characteristics that preceded animal flight - reveals that these shifts occurred concurrently.

"We were really surprised to discover that the key size shifts happened at the same time, at the origin of Paraves," Puttick said, referencing the dinosaur group more closely related to birds than the feathered dinosaurs called oviraptorosaurs. "This was at least 20 million years before the first bird, the famous Archaeopteryx, and it shows that flight in birds arose through several evolutionary steps."

Puttick and his colleagues learned that there was an entire group of dinosaurs that were small, lightweight and had wings of some sort, and that they all preceded Archaeopteryx. Most of these creatures, it appears, used their feathered wings to glide rather than as a means of powered flight, the researchers said.

"Out of all these flappers and gliders, only the birds seem to have been capable of powered flight," said co-author Mike Benton, a professor of Vertebrate Palaeontology at University of Bristol. "But you wouldn't have picked out Archaeopteryx as the founder of a remarkable new group."

The researchers applied a new calculation method to determine the rate of evolution of different characteristics related to flight and applied it across the ancient evolutionary tree, identifying where bursts of rapid evolution occurred.

"Up to now you could only have guessed roughly where the major evolutionary transitions occurred, but the new methods pinpoint the size changes. The small size of birds and their long wings originated long before birds themselves did," said study co-author Gavin Thomas of the University of Sheffield.

The first feathered dinosaurs were found in China in the 1990s, and at the time it was believed that birds were the result of a rapid evolution from dinosaurs. But now appears that the marked transformation occurred at a slower pace.

"The origin of birds used to be seen as a rapid transition," Puttick said "but now we know that the key characteristics we associate with them arose much earlier."