Fluffy Dinosaur Raises Questions About the Origin of Dinofuzz

Almost twenty years after fluffy little Sinosauropteryx hopped onto the scene, the existence of feathery dinosaurs is no longer much of a surprise. Paleontologists have found evidence of body coverings from “dinofuzz” to flight feathers on a score of non-avian dinosaur species, ranging from the pigeon-sized, magpie-patterned Anchiornis to the 30-foot long Yutyrannus. But despite this flood of fossil discoveries, paleontologists are still puzzling over the bigger questions behind the plumage. Among the most pressing is when these downy splashes of fluff and fuzz first evolved. A newly-named dinosaur found in Siberia only complicates the question.

Late last year, at the annual Society of Vertebrate Paleontology meeting in Los Angeles, experts and amateurs crowded into a presentation hall to see Royal Belgian Institute of Natural Sciences paleontologist Pascal Godefroit present a new feathered dinosaur. The buzz around the specimen, fueled by the conference program, was that the dinosaur in question was an ornithischian.

Most feathery and fluffy dinosaurs found so far are theropods. This is a major dinosaur subgroup that includes birds and their close relatives, as well as carnivorous terrors like Ceratosaurus and weirdos like Therizinosaurus, going all the way back to where this “beast footed” lineage split from all other dinosaurs. But the dinosaur Godefroit was set to unveil was all the way on the other side of the dinosaur family tree. Ornithischians included the armored, shovel-beaked, and horned dinosaurs, among others, and were as distantly-related to birds as it was possible to be while still being dinosaurs. That’s what made a fluffy ornithischian so strange.

Paleontologists had found two different ornithischians with peculiar body coverings before. In 2002 Gerald Mayr and colleagues announced bristle-like structures jutting from the tail of Psittacosaurus, an early horned dinosaur, and in 2009 Xiao-Ting Zheng and coauthors described Tianyulong, an archaic form of dinosaur called a heterodontosaurid with a mane of similar quills. Together, these animals raised two alternatives: either dinosaurs evolved feather-like body coverings multiple times, or wispy body coverings were an ancestral trait that went all the way back to the last common ancestor of all dinosaurs.

Godefroit’s animal promised to add one more data point to this cluster of flashy ornithischians. Sadly, he couldn’t present his animal during the SVP meeting. Excited dinomaniacs, myself included, trudged out of the hall and into other concurrent sessions. From a geologic perspective, though, the wait for the details hasn’t been long. Today, Godefroit and colleagues have presented their peculiar dinosaur, named Kulindadromeus zabaikalicus, in the pages of Science.

This new dinosaur is already known from a wealth of material. A pair of bonebeds, estimated to be between 169 and 144 million years old, yielded “six partial skulls and several hundred disarticulated skeletons” of Kulindadromeus scattered through the remnants of a Jurassic lake. The bones showed the five-foot-long dinosaur to be a neornithischian, a bipedal herbivore that was not so archaic as Tianyulong but not so specialized as the hadrosaurs or horned dinosaurs. And some of these skeletons not only included different types of scales, but what Godefroit and colleagues interpret as “avianlike feathers.”

In terms of typical dinosaur tubercles, Kulindadromeus had hexagonal scales on its lower legs, rounded scales around the hand and ankle, and rows of large scales along the tail. But the fossils also preserved a trio of feathery structures. Single filaments surrounded the dinosaur’s head, torso, and back, while the dinosaur’s upper arms and legs were covered in multi-filament plumes and the dinosaur’s lower leg sported “ribbon-shaped elements” that have not been seen in any other species so far.

The question is whether these fluffy structures are true feathers or fluffy imitations. This has major implications for when true feathers and their immediate forerunners evolved in dinosaurs. If the dinofuzz on Kulindadromeus really is equivalent to that borne by theropods like Sinosauropteryx, then the beginnings of feathers probably coincided with the origin of dinosaurs. If the structures are superficially the same, but not truly equivalent, then feather-like structures either evolved more than once or diverged from some earlier, as-yet-unseen type of integument.

For the moment, there’s still no way to distinguish between these alternative scenarios. At a basic anatomical level paleontologists have yet to discern whether the structures on Psittacosaurus, Tianyulong, and Kulindadromeus can truly be called feathers. Not to mention the need for better fossils of older dinosaurs, close to where the major lineages split, to follow feather origins, as well as a more refined understanding of the circumstances under which fluff, fuzz, and bristles are likely to be preserved.

But while the headline that “all dinosaurs had feathers” stretches the evidence too far, Godefroit and colleagues are correct that dinosaurs probably sported a variety of filamentous body coverings in addition to scales.

Feathers or scales aren’t mutually exclusive – look at the feet of a chickadee or pigeon sometime – but are different kinds of body coverings that non-avian dinosaurs wore in startling combinations. This opens up tantalizing possibilities for familiar dinosaurs whose outer appearances are still poorly known. Imagine Allosaurus with whisker-like wisps around its face to help it better nab prey, or an Apatosaurus with a shock of fluff running down its back. I have no doubt that as paleontologists uncover more and more dinosaurs with weird, fuzzy body coverings, our image of what a dinosaur is will become ever-stranger.

Reference:

Godefroit, P., Sinitsa, S. Dhouailly, D., Bolotsky, Y., Sizov, A., McNamara, M., Benton, M., Pagina, P. 2014. A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. Science. 345, 6195: 451-45