According to new research on the first birds and bird-like dinosaurs (Paraves) which lived 160 to 120 million years ago, bird wings and small body size arose much earlier than scientists previously believed.
Archaeopteryx lithographica, one of early birds. Image credit: H. Raab / CC BY-SA 3.0.
“We were really surprised to discover that the key size shifts happened at the same time, at the origin of Paraves,” said Mr Mark Puttick from the University of Bristol, UK, the lead author of a paper published in the journal Evolution.
“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.”
Being small and light is important for a flyer, and it now seems a whole group of dozens of little dinosaurs were lightweight and had wings of one sort or another. Most were gliders or parachutists, spreading their feathered wings, but not flapping them.
“Out of all these flappers and gliders, only the birds seem to have been capable of powered flight,” said study senior author Prof Mike Benton, also from the University of Bristol.
“But you wouldn’t have picked out Archaeopteryx as the founder of a remarkable new group.”
Rates of femur and forelimb evolution in Theropoda. Red branch leading to the Paraves indicates a 200-fold rate increase relative to the background rate. Image credit: Mark N. Puttick et al.
Mr Puttick and his colleagues applied new numerical methods that calculate the rate of evolution of different characteristics across a whole evolutionary tree, and identify where bursts of fast 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 co-author Dr Gavin Thomas from the University of Sheffield.
Birds owe their success to their flight, wings and feathers. Until the 1990s, when the first feathered dinosaurs were found in China, birds were thought to have originated rapidly, marking a major transition from dinosaurs.
Now, paleontologists know that Archaeopteryx was only one of a large number of small, flying dinosaurs.
“The origin of birds used to be seen as a rapid transition, but now we know that the key characteristics we associate with them arose much earlier,” Mr Puttick said.
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Mark N. Puttick et al. High rates of evolution preceded the origin of birds. Evolution, published online February 23, 2014; doi: 10.1111/evo.12363
