Now that my book’s turned in, I have a chance to catch up on the stack of biology papers I’ve had to neglect. I hope to be posting more about them in the next couple of weeks, but be aware that the Dreaded Edits to the book will come back when I’ve returned from Poland, and that, along with dealing with references, formatting, and the like, will probably take a few months of work.
But, in the meantime, there’s a a cool new paper in Nature Communications by Gang Han et al. (reference and download below) describing the discovery of a four-winged dinosaur in fossil deposits from the Early Cretaceous (about 125 million years ago) in China. As you know, most of the good feathered dino fossils come from China, for that country has marvelous deposits of silt that produced good preservation of feathers.
Your first question will be this: could it fly? The answer is “we don’t know.” (That’s often true of these feathered dinos, which could have been gliders rather than fliers). And this is not the first “four-winged” dinosaur. What’s notable about it is its size (BIG) and its highly feathered tail.
Also, do remember that four-winged dinosaurs didn’t really have four wings: they usually had front appendages that were winglike and highly feathered, but legs that were less feathered. They also had bony tails, like all dinos, which were also feathered.
None of them, as far as I remember, can definitely be said to have flown: they could have been gliders, and could have glided to escape predators, to move from tree to tree, to glide down on prey, or all of the above. The first one discovered was Microraptor gui, which looked something like this:
That out of the way, the new species is named Changyuraptor yangi. “Changyu” means “long feather” in Chinese, “raptor” refers to the fact that it was a predator—see teeth below—and the species name honors Professor Yang Yudong, who apparently provided the finances to purchase the fossil.
It’s a theropod dinosaur, the ancestors of birds, and falls in the family Dromaeosauridae, a group of bipeda (walked on its hind legs) and predatory theropods. The specimen, shown below, is remarkably well preserved, at least below the neck. But there are parts of the head and the teeth remaining. In the fossil below you can make out the feather impressions along the neck, the forelimbs, the hindlimbs, and along the long, bony tail (remember, this was a dinosaur, not a tailless bird!). The length of the black line at the bottom is 10 cm (about 4 inches), so the thing was about 132 cm long from the tip of the beak to the tip of the tail. That’s 51 inches, or about 4.25 feet, so this is a large specimen!
Here’s a reconstruction of the skeleton with the feather impressions shaded in. The section at the bottom is a bit of the femur impression, showing the “LAG,” or “line of arrested growth,” from which the authors conclude that this was an adult specimen, at least five years old.
Some details of the skeleton: a. tail vertebrae, b. some of its teeth (notice they’re sharp; these things, like other feathered dinos, these were predators; c. furcula (“wishbone”) and shoulder girdle, and d. a foot. The scale bar is 1 cm.
Here are impressions of the feathers (see caption below the photo for details). The authors conclude that this species had the longest feathers of any known “non-avian dinosaur” (I’m checking with the experts to see exactly what distinguishes a “non-avian dinosaur” from either an “avian dinosaur” or a “bird”). The tail feathers were up to 30 cm long—almost a foot. That exceeds by several inches the longest known feathers in similar dinosaurs, but of course this was one of the largest flying/gliding dinosaurs.
As I said, this is a well-feathered dino, but the authors still can’t conclude that it flew. That, I suppose would depend both on finding better feather impressions (flying feathers are asymmetrical) and knowing something about the musculature, which isn’t preserved. This is above my pay grade, but I suppose it’s almost impossible to conclude from a fossil of this type whether it flew, even if the feathers were asymmetrical. But at the very least it glided, and probably well.
The authors make a big deal about the feathered tail, wondering what function it served for a glider. They conclude it controlled “pitch”, or the ability of the animal to control its movement from “head up” to “head down”. That is, imagine the bird with wings extended and a rod stuck through the wings from one side to the other. You could then move the body up and down like a seesaw (head goes up, tail goes down) around this axis (see here for a demonstration). That would enable the bird to make a good landing if it were coming in from above. But here, I’ll let you read the conclusion, since it’s not too technical (my emphasis):
Combined with the possibility of passive flexion of the distal tail to take on both positive and negative angles of attack, this caudally oriented combination of lift and drag may have acted to reduce descent speed while simultaneously providing passive stability in the pitching axis, which could be critical to a safe landing or precise attack on prey. Such pitch stabilization could be particularly important for larger microraptorines (since they would tend to fly and/or descend more rapidly than small individuals), and this effect explains why the tail fan is exceptionally long in HG B016 [the specimen]. A pitch control function also explains why the feathered tails of microraptorines are proportionally much longer than in other maniraptorans, as this would extend the moment arm for pitch control by the tail. The discovery of HG B016 thus supports the hypothesis that the extended tail and long, fanned retrices of microraptorines played a key aerodynamic role, allowing them to retain aerial and/or semi-aerial competency at relatively large body sizes. The remarkably long-feathered tail Changyuraptor yangi helps us understand how such low-aspect-ratio tails operated as pitch control structures that reduced descent speed during landing.
If I had a time machine, and could go back to, say, five periods of evolutionary history, one of them would be this time, so we could see exactly what these beasts looked like and whether they flew. (A thought experiment I often think about is this; if you’re given a machine to go back to one time in evolutionary history, and were given only a notepad and pen, where and when would you go to answer the most pressing and difficult questions of evolution?)
Han, G., L. M. Chiappe, S.-A. Ji, M. Habib, A. H. Turner, A. Chinsamy, X. Liu, and L. Han. 2014. A new raptorial dinosaur with exceptionally long feathering provides insights into dromaeosaurid flight performance. Nature Communications : doi:10.1038/ncomms5382