Scales, Fuzz, and Feathers

February 10, 2017

 

Scales, Fuzz, and Feathers
With all the buzz about Jurassic World floating about the internet, you’ve probably wondered whether dinosaurs were scaly or feathery. The lack of feathery dinosaurs forms one of the more common complaints about the film coming from both armchair and professional paleontologists. Unfortunately, the tendency of the media to generalize and oversimplify muddles the issue into an either/or proposition. In fact, dinosaurs had a wide variety of skin textures and degrees of apparent featheriness or scaliness, much like the birds and reptiles of today.
How can we tell what dinosaur skin looked like? Rare fossils do leave skin impressions. Such fossils have shown that Diplodocus had an iguana-like mane of spiky-looking scales along its back, neck and tail. Carnotaurus had crocodile-like armor as portrayed here at the park. A juvenile Allosaurus was found with scaly skin impressions, contradicting depictions in children’s books of fluffy allosaur chicks. Numerous duck-billed hadrosaur “mummies” have been found, showing their skin had a pebbly texture like a giant basketball. The park has skin samples from a hadrosaur called Gryposaurus—feel free to ask about them at the Science Education Center located on the eastern end of the park.
Those dinosaurs that did have feathers in most cases had a variety of feather designs as well as scales or possibly bare skin on different areas of the body. Some of these feathery structures, often called “protofeathers,” looked more like hair than feathers on most birds today. Some dinosaurs also sported the more familiar pennaceous feathers, which have a stiff shaft with Velcro-like barbs, as found on the flight feathers of modern birds. A few types of dinosaurs may even have grown the floppy, decorative plumaceous feathers.
On the feathery side, the evidence comes from a few different lines. Again, skin impressions show feathers or protofeathers on small, bird-like theropods like Sciurumimus. Microraptor had flight feathers preserved on both its arms and legs. Larger dinosaurs like Therizinosaurus, Deinocheirus, or Yutyrannus may have had shaggy protofeathers on parts of their bodies. Scientists have also found different kinds of protofeathers preserved in Canadian amber which also give us an idea of color pattern (if not exact coloration). Finally, some Velociraptor arm bones show small bumps that served as attachment points for long, stiff feathers along their arms much like the primary feathers of a bird’s wing.
Most evidence for feathers comes from the theropod dinosaurs (the bird-like meat-eaters, for the most part), but some of the bird-hipped plant eaters had strange, feather-like structures covering their skin as well. Psittacosaurus—a housecat-sized relative of Triceratops—for example, had long whisker-like quills on its tail. Tianyulong, another small, bird-hipped dinosaur, sported long, stiff quills over much of its body. Discoveries like this led to a recent media story that may lead to the incorrect impression that all dinosaurs had feathers. The evidence does not support that generalization; any group of dinosaurs might have had feathers at some point in their evolutionary history, or something vaguely like them, but some species were clearly scaly. In fact, a 2015 study of available dinosaur skin fossils determined that other than theropods, most dinosaurs bore scales. The crucial evidence from early dinosaur times remains unknown, but the study concluded that a feathery dinosaur ancestor seems unlikely at this point.
With what we know so far, dinosaurs seem more likely to have experimented with skin coverings, which makes new discoveries even more important (and exciting). It’s more than just scales vs. feathers, too: some dinosaurs may have had skin coverings seen in no other animal. For most dinosaurs, we just don’t have clear evidence for what covered their skin, and we have to infer skin texture as a result. New fossil discoveries or study techniques can overturn those inferences at any time. —Jeff Bond

 

Barrett, Paul M., David C. Evans, and Nicolás E. Campione. "Evolution of dinosaur epidermal structures." Biology letters 11.6 (2015): 20150229. http://rsbl.royalsocietypublishing.org/content/11/6/20150229?TB_iframe=true&width=921.6&height=921.6

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