IN THE EARLY stages of evolving flight, feathered dinosaurs tried an interesting experiment: they developed four wings.
These small dinosaurs – such as Microraptor, Anchiornis and Xiaotingia – had large flight feathers on their hind limbs as well as their fore limbs, and they had long bony tails, similarly replete with large feathers.
It appears that many early birds, such as Archaeopteryx, may also have had long feathers on their hind limbs. It was only later that birds developed the characteristically bald legs that (most) birds have today, and became aerodynamically stable on two wings and a much-reduced tail.
Microraptor was the first of the four-winged dinosaurs to be discovered, in 2003, and it was tiny for a dinosaur: approximately 1kg in weight and similar to a crow or a raven in size. Miniaturisation, experts thought, was an essential step in developing flight. But now a totally new four-winged dinosaur has been discovered, and it was much larger.
Largest four-winged dinosaur
Changyuraptor yangi – described for the first time today in the journal Nature Communications – would have been around 4kg in weight and about the size of a turkey. It also has a really unusual feature: an incredibly long tail with 30cm feathers that trailed out behind the body. These tail feathers were around 30 per cent of the length of the skeleton, making them the longest known feathers of any (non-bird) dinosaur.
The 125-million-year-old fossil of the species, discovered in China’s Liaoning Province, preserves the feathers of the animal in incredible detail. Liaoning has been the source of many thousands of specimens of more 35 species of feathered dinosaurs since the first was uncovered there in 1996 (here's a full list of feathered dinosaurs).
Some of the dinosaurs could fly - or at least glide - but the majority used their feathers for insulation or display.
The authors of the paper are an international team including Gang Han and Lizhua Han at Bohai University in China, and Dr Luis Chiappe at the Natural History Museum of Los Angeles County in the US.
They argue that the long flight feathers on Changyuraptor's tail were an adaptation that allowed this relatively large animal to land without fear of crashing into the ground, which becomes more of a problem for large flying animals. The tail would have helped it to control its speed of descent and also limited it from pitching backwards or forwards as it came down.
No ungainly crash landings for Changyuraptor
"The long bony tail of Changyuraptor, and the foot-long feathers it sported, are unlike the short tails in modern birds," co-author Dr Alan Turner of New York’s Stony Brook University told reporters. "So how it functioned aerodynamically would have been quite different from living birds. However, this is exactly the sort of tail we see in the earliest birds and their immediate precursors, which means avian flight evolved in animals with long tails. Changyuraptor provides an excellent opportunity to investigate just what this tail might have been good for."
"Numerous anatomical features and behaviours that we have long associated with birds in fact evolved in dinosaurs long before the first birds arrived on the scene," Alan said.
"This includes hollow bones, nesting behaviour, feathers, and possibly flight. There is a growing diversity of feathered dinosaurs close to the origin of birds that many research groups are looking at to understand how gliding or flight aerodynamics evolved, and whether these traits were inherited by the earliest birds."
Changyuraptor is just one of a fascinating series of new discoveries that are revolutionising our ideas about how birds first began to fly. And those discoveries are coming thick and fast. Watch this space!
John Pickrell is the author of Flying Dinosaurs: How fearsome reptiles became birds, published by NewSouth Books in June 2014. Follow him on Twitter @john_pickrell.