Wings! Specifically, dinosaurs

Feathered wings are among the most beautiful and captivating things in nature, and also among the most complex and difficult things to capture artistically. To aid in the quest to represent wings in fiber, I think it is important to understand the form and purpose of the parts of the wing.

There are about ten million different subjects we could talk about in relation to wings: non-flight uses for bird feathers and wings, the morphology (wing shape) between different birds to achieve different flight patterns, evolution of wings, the names and places of all the feathers, the function and chemistry of wing oils, the muscular and skeletal anatomy, the homology or synapomorphy between wings and human arms…etcetera etcetera etcetera. (Those links should take you to decent starting points, just in case any of those topics sounded particularly interesting to you. Except the synapomorphy links, three of which are actual scientific papers.)

Obviously, that’s too much for any one article (which is why I linked fifteen), so I’m narrowing my focus. I’ve been trying to design a Velociraptor, so we’re going to talk specifically about 1) the fossil evidence for dinosaur wings, because for some reason it’s still a debate and I relish the fact that there is really good evidence for fluffy dinos, and 2) what uses dinosaurs had for wings.

Velociraptor by ChrisMasna on deviantART. The coloring here is speculative, but the feather reconstruction is not.

Velociraptor was part of a family of dinosaurs called Dromaeosauridae, the members of which are referred to as dromaeosaurs. They are characterized by their body type–bipedal, with smaller arms, long tails, graceful necks, and probable covering of feathers. Many dromaeosaurs are known only from skulls or from incomplete skeletons, lacking evidence of feathers or even any particular kind of skin altogether. However, Velociraptor is known from almost complete skeletons.

hartman-velociraptor

Skeletal by Scott Hartman; above, the known parts of the skeleton, and below, the inferred complete reconstruction.

The specific skeletal evidence of feathers on Velociraptor? Quill knobs on the ulna (one of the two paired bones on the lower arm).

F1.large

A is a Velociraptor ulna; B is the closeup of the red box in A. C through F are comparative shots of what modern day turkey quill knobs look like. From Turner et. al. 2007.

Quill knobs are small bumps or marks on the bones of a bird. They exist because flight feathers often need to be attached more strongly than other feathers, due to the stress they endure. The absence of quill knobs doesn’t mean there were no feathers; flamingos lack quill knobs, but are still feathered. However, quill knobs are a direct indication of highly developed feathers such that modern birds have today. Other dromaeosaur species like the large, recently-discovered Dakotaraptor also had quill knobs, suggesting it was a trait shared among most dromaeosaurs (DePalma et. al., 2015).

Closely related species have been found with halos of feathers around their bones, showing where their feathers existed in life. I find these fossils a particularly haunting picture of these past animals, and one of the most interesting is Microraptor. A basal (belonging to a base; “less” evolved) dromaeosaur, Microraptor and animals like it are what the rest of the dromaeosaur family evolved from (Xu et. al., 2003).

Microraptor_gui_holotype

The Microraptor holotype, or definitive identifying fossil. From Hone et. al. 2010.

You can see a tail fan, wings on both front arms, and curiously enough, wings on the back legs. The feathers are marked out on the rock like they were burned there; in fact, they were well-preserved enough that scientists were able to collect melanosomes (organelles responsible for pigment in animals) and discover that Microraptor was black, with iridescent feathers like a raven (Li et. al. 2012).

Honestly, these kinds of discoveries are why I wanted to be a paleontologist when I was tiny. I remember dinosaur books when I was six or seven saying “We have no way of knowing what colors dinosaurs might have been!” and now here we are, and it turns out we can know. Sinosauropteryx and Anchiornis have also had significant amounts of their colors mapped by science, and this diagram by tumblr user albertonykus shows pretty well the other fragments of fossil dinosaurs we have colors from.

Microraptor was using its wings to fly, but despite being relatively small Velociraptor was too heavy to get off the ground. Plus, even huge predators like Yutyrannus (an arctic relative of Tyrannosaurus) had feathers. What were they using their wings for if not flight?

Feathers on their own are useful for display and heat regulation, but wings themselves seem specialized especially for aerodynamics. They are, of course, but that’s not the only thing they can be used for, just like our feet are specialized for walking but can also be used to deliver a mean kick.

There are three main theories that I know of: wing-assisted incline running, stability flapping/wings as balancers, and wings as weapons.

Wing-assisted incline running is the use of a flapping motion of the wings as the animal runs to create extra momentum and allow it to run up near-vertical slopes. This is employed by many modern birds, most notably the chukar partridge. Hatchlings of many other modern species who are not fully capable of powered flight yet use the technique, and interestingly enough, even adults capable of powered flight will preferentially use wing-assisted incline running to get to refuge (Dial 2003). Though of course no dromaeosaur has ever been documented doing any running, since they’re all dead, it fits neatly with locomotive analyses of dromaeosaurs as fast and agile predators. Using their wings to run up inclines, they could achieve even greater feats of agility, and even climb trees to catch prey or avoid larger predators.

http://emilywilloughby.com/gallery/paleoart/deinonychus-prey-restraint

Deinonychus on top of prey, using stability flapping to keep its balance. By Emily Willoughby.

Stability flapping is a theory based on the hunting abilities of dromaeosaurs. A key feature of the famous dromaeosaur species is the terrifying sickle claw on their feet, which would have been used to kill prey. Like modern predatory raptors, the dinosaur would then have used its feet to hold down its prey while it fed or finished the kill. Since its feet would be locked into a struggling animal, it couldn’t use them to keep its balance, so it would use its rigid, fanned tail and wings to stay upright (Fowler et. al. 2011). Alternatively, wings could be used as stabilizers while running, as this fascinating article about ostriches suggests.

The final theory, wings as weapons, is pretty much what it says on the tin. Many, many modern birds maintain spurs, claws, and clubs on their wings to increase their potential as weapons, and this ancient ibis had thickened forearm and hand bones so that it could swing its wing as a club. As a precursor to aggression, wings can also be used as a display to make the animal appear bigger.

And finally, we get to what I did with all this information.

wing

It’s late and all the lighting in my house is terrible.

This was a basic chevron pattern that I continued for a few rows, alternating FLO and BLO so that there would be extra loops on one side of the chevrons. Then I chained up the side and started making feathers in the unworked loops. Each long feather (remiges) is  (ch6, sk 1st ch, sc in next ch, sc in each ch st, sl st in next sc) and the middle feathers (coverts) start with a ch4.

It’s really scrunched up but I’m pleased with the look so far. I just need to adjust the chevron stitch (you’re really supposed to have at least one full W shape with the pattern I used, so stopping halfway made it do some funny things on the return rows) and where the feathers go so they lay more naturally. And then I need to mirror the entire thing to make the left wing… but for sure, I’m having fun.

I love dinosaurs.

Citations

DePalma, R. A., Burnham, D. A., Martin, L. D., Larson, P. L., & Bakker, R. T. (2015, October 30). The first giant raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation. Paleontological Contributions PC. doi:10.17161/pc.1808.18764

Dial, K. P. (2003, January 17). Wing-Assisted Incline Running and the Evolution of Flight. Science, 299(5605), 402-404. doi:10.1126/science.1078237

Fowler, D. W., Freedman, E. A., Scannella, J. B., & Kambic, R. E. (2011, December 14). The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds.PLoS ONE, 6(12). doi:10.1371/journal.pone.0028964

Hone, D. W., Tischlinger, H., Xu, X., & Zhang, F. (2010, February 15). The Extent of the Preserved Feathers on the Four-Winged Dinosaur Microraptor gui under Ultraviolet Light. PLoS ONE, 5(2). doi:10.1371/journal.pone.0009223

Li, Q., Gao, K., Meng, Q., Clarke, J. A., Shawkey, M. D., D’alba, L., . . . Vinther, J. (2012, March 08). Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science, 335(6073), 1215-1219. doi:10.1126/science.1213780

Turner, A. H., Makovicky, P. J., & Norell, M. A. (2007, September 21). Feather Quill Knobs in the Dinosaur Velociraptor. Science,317(5845), 1721-1721.
doi:10.1126/science.1145076

Xu, X., Zhou, Z., Wang, X., Kuang, X., Zhang, F., & Du, X. (2003, January 23). Four-winged dinosaurs from China. Nature, 421(6921), 335-340. doi:10.1038/nature01342

 

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