Smithsonian.com

Not only was Ornithomimus feathered, but the dinosaur’s fluffy coat changed as it aged. Lovely art by Julius Csotonyi.

Another week, another feathery dinosaur. Since the discovery of the fluffy Sinosauropteryx in 1996, paleontologists have discovered direct evidence of fuzz, feather-like bristles and complex plumage on over two dozen dinosaur genera. I love it, and I’m especially excited about a discovery announced today. In the latest issue of Science, University of Calgary paleontologist Darla Zelenitsky adds another enfluffled species to the dinosaurian ranks. Even better, the specimens raise hopes that many more dinosaurs might be preserved with their feathery coats intact.

Zelenitsky’s downy dinosaurs are not newly discovered species. Ornithomimus edmontonicus was initially described by famed bone hunter C.H. Sternberg in 1933, and it is one of the characteristic Late Cretaceous species found in Alberta, Canada’s fossil-rich Horseshoe Canyon Formation. In Sternberg’s time, these dinosaurs were thought to be scaly, but recent finds of so many feathery dinosaurs has raised the likeliehood that the “ostrich mimic” dinosaur was at least coated in some sort of dinofuzz.

A family tree of Saurischian dinosaurs, showing lineages within this group with direct evidence for feathers. From Zelenitsky et al., 2012.

The prediction of fluffy Ornithomimus came from the spread of feathers on the coelurosaur family tree. The Coelurosauria is a major dinosaur group that encompasses tyrannosaurs, compsognathids, ornithomimosaurs, alvarezsaurs, oviraptorosaurs, deinonychosaurs and birds. To date, evidence of feathers has been found in every coelurosaur lineage except one–the ornithomimosaurs. The spread of feathers hinted that some sort of plumage was present in the common ancestor of all coelurosaurs and therefore should have been inherited by the ornithomimosaurs, but, until now, no one had found direct evidence.

A trio of Ornithomimus skeletons have finally confirmed what paleontologists expected. Zelenitsky enthusiastically explained the details to me by phone earlier this week. In 1995, when Zelenitsky was a graduate student, paleontologists uncovered an articulated Ornithomimus with weird marks on its forearms. No one knew what they were. But in 2008 and 2009 a juvenile and an adult Ornithomimus turned up with preserved tufts of filamentous feathers. “When we found these specimens,” Zelenitsky said, “we made the link to the 1995 dinosaur.” All those strange marks on the arms of the previously discovered Ornithomimus, Zelenitsky and colleagues argue, are traces of longer, shafted feathers.

Even though paleontologists expected feathery Ornithomimus, the discovery was still a surprise. “I was in disbelief,” Zelenitsky said. “They’re the first feathered dinosaurs from the Americas, and the first ornithomimosaurs with feathers, as well. It was shocking to say the least.”

But there’s more to the find than simply adding another species of fluffy dinosaurs to the list. The fact that the adult and juvenile animals had different kinds of plumage adds new evidence that coelurosaurs changed their fluffy coats as they aged. “The one juvenile was completely covered in filamentous type feathers,” Zelenitsky said. What the adults looked like comes from the two other specimens. One adult skeleton, lacking forearms, preserves fuzzy feathers, and “the second adult had markings on the forearm.” Together, the specimens indicate that adult Ornithomimus were mostly covered in fuzz but developed more complex arm feathers by adulthood.

Sex is probably behind the plumage change. “We infer that because these wing feathers are not showing up until later in life, they were used for reproductive purposes,” Zelenitsky said. Perhaps adult Ornithomimus used flashy arm feathers to strut their stuff in front of potential mates. Then again, based upon the resting and brooding postures of other theropod dinosaurs, adult Ornithomimus could have used their proto-wings to cover their nests. We don’t know for sure, but the developmental change appears to be another example of dinosaurs undergoing significant changes as they approach sexual maturity. This discovery, and others like it, will undoubtedly play into the ongoing discussion about the role of sexual selection in dinosaur biology and evolution.

Best of all, the new study indicates that paleontologists may soon find more feathered dinosaurs in unexpected places. The Ornithomimus skeletons were found in prehistoric river deposits composed of sandstone. Since almost all feathered non-avian dinosaurs have been found in fine-grained sediment–such as those around Liaoning, China–paleontologists thought that coarser-grained sandstone deposits were too rough to record such fine details. Now we know better. “That’s the really exciting part of it,” Zelenitsky says. If traces of dinosaur feathers can be preserved in sandstone, the twist opens up the possibility that paleontologists might find fluff and feathers with a greater array of dinosaurs–including the tyrannosaurs, deinonychosaurs, therizinosaurs and other coelurosaurs of North America. The trick is recognizing the traces before they’re destroyed during excavation and preparation. Rock saws and airscribes can all too easily obliterate the delicate fossils. A word to researchers–keep your excavation tools sharp, and your eyes sharper.

Reference:

Zelenitsky, D., Therrien, F., Erickson, G., DeBuhr, C., Kobayashi, Y., Eberth, D., Hadfield, F. 2012. Feathered non-avian dinosaurs from North American provide insight into wing origins. Science. 338, 510-514

Triceratops at the Smithsonian National Museum of Natural History. Photo by the author.

Triceratops was an A+ dinosaur. But, awesome as the hulking ceratopsid was, it didn’t have mutant superpowers. Indeed, despite a website’s claim to the contrary, there’s no evidence that this three-horned behemoth defended itself with poisonous quills.

Even though it was posted over a year ago, I’ve received a few emails this week asking about a Listverse post by user “TyB” titled “Top 10 Dinosaurs That Aren’t What They Were.” For the most part, the list is a simple summary of how new discoveries and ideas have revitalized images of dinosaurs. When the article gets to Triceratops, though, the scientific accuracy careens off the rails.

Rather than being covered in smooth, wrinkly skin, the article states, Triceratops had “alligator-like, flat scales, called scutes, on its belly, and the rest of its body was covered in large scales and knobs.” I don’t know of any published study on Triceratops’ body covering, but it wouldn’t be surprising if, like other dinosaurs, Triceratops had bumpy skin with larger knobs or ornaments here and there. But here’s where things get strange:

Its back and tail also had a series of weird, fist-sized bumps, each one holding a nipple-like structure which has yet to be explained by scientists. These structures may very well be anchoring points for porcupine-like quills, like those found on Triceratops’ older cousin, Psittacosaurus. Or perhaps, some scientists suggest, they were poison glands, oozing toxins to protect the Triceratops’ hindquarters from T-Rex attacks.

I have no idea what this blogger is talking about. I had never heard the idea of a poisonous Triceratops before reading the list, and I don’t know of any paleontologist who has advocated such a notion. I think I know where the post’s author got the basis for their idea, though. For years, there have been rumors of a Triceratops–now on display at the Houston Museum of Natural Science–that was preserved with skin impressions and possible evidence of bristles along the tail. The scuttlebutt, along with evidence of feather-like bristles in the archaic ceratopsian Psittacosaurus, spurred artists to start putting tufts of quills on Triceratops tails.

No one has formally published a description of these structures, though. Whether they’re truly bristles, some other true body covering or a preservational artifact is unknown. It’s not unreasonable to think that Triceratops had patches of bristles, but the truth is that there’s no positive evidence that such ornamentation actually adorned the dinosaur, either.

But I’m confounded by the suggestion that the base of the quills provided space for “poison glands.” Bristles on Triceratops are iffy to start with, and no one has ever demonstrated that dinosaurs used venom or other toxins for defense. In 2009, one group of researchers proposed that the feathered, sickle-clawed Sinornithosaurus had a venomous bite, but their suggestion was quickly refuted. There’s so evidence that dinosaurs were venomous, poisonous, toxic or otherwise relied on biological warfare. As far as I can tell, the toxic Triceratops is entirely the invention of the list’s author.

That’s not all. In the same post, the author states that “After examining the beak and jaws, paleontologists reached the conclusion that Triceratops may have been partially carnivorous, probably scavenging after T-Rex, or even scaring smaller predators away from their kills.” Again, no one has actually studied this in detail, but, unlike the poison hypothesis, this idea is actually plausible.

Paleontologist and artist Mark Witton raised this point in a description of a gorgeous Styracosaurus illustration he drew a few years ago. As Witton pointed out, the scissor-like jaws of big ceratopsids were probably capable of slicing through flesh as well as plants, and it’s not unreasonable to think that these dinosaurs occasionally picked over meaty carcasses to supplement their diets with some protein. After all, as paleontologist Darren Naish has illustrated, cows and deer do the same thing today. Herbivores can indulge in a meaty meal, just as carnivores sometimes chomp fruit and greens. What we need now is someone to model how a Triceratops skull would handle munching on flesh and bone to put some more science behind the speculation.

The skeleton of Sciurumimus, seen under UV light. You can see traces of protofeathers alon the dinosaur’s tail. Photo by Helmut Tischlinger.

On Monday, the world met yet another fuzzy dinosaur. The little theropod – named Sciurumimus albersdoerferi – is beautifully preserved in a slab of roughly 150 million year old limestone found in Germany. (These deposits have also brought us Archaeopteryx and the also-fluffy Juravenator.) And, with a little evolutionary context, Sciurumimus hints that filament-like protofeathers were more common among dinosaurs than we previously expected.

Birds – the only surviving lineage of dinosaurs – are covered in plumage. No surprise there. But since 1996, paleontologists have identified about 30 genera of non-avian dinosaurs with feathers. Most of these dinosaurs are coelurosaurs – the major group of theropod dinosaurs that contains tyrannosaurs, the switchblade-clawed deinonychosaurs, the truly weird therizinosaurs, and, among others, birds. As the discoveries accumulated, it seemed that feathers originated at the base of this group, and were inherited by birds. And feathers were not only present an small, especially bird-like dinosaurs. As the recently-described Yutyrannus shows, even 30-foot-long tyrannosaurs were fluffy.

Up until a few years ago, birds and their closest non-avian relatives were the only dinosaurs known to have feathers. Simple enough. But then two ornithischians crashed the party.You see, the dinosaur family tree is split into two halves – the saurischians on one side, and the ornithischians on the other. The split goes back about 230 million years or so, nearly to the origin of the very first dinosaurs.

The feathery coelurosaurs belong to the saurischian side of the tree, but paleontologists have also discovered dinosaurs on the other side – on the ornithischian branches – with feather-like structures. In 2002, paleontologists discovered that the archaic ceratopsian dinosaur Psittacosaurus had a brush of bristle-like structures jutting from its tail. And in 2009, another team discovered Tianyulong – another ornithischian dinosaur with a row of similar filaments running down its back. The bristles were not just like the fuzz and feathers seen among the coelurosaurs, but they were structurally similar.

Paleontologists were left with two possibilities. Either protofeathers evolved multiple times in different dinosaur lineages, or simple “dinofuzz” was an ancestral dinosaur feature that was later lost in some lineages. We don’t have enough fossils yet to know for sure, but the discovery of Sciurumimus is a significant clue that most, if not all, dinosaur lineages were at least partially decorated with protofeathers.

Even though Sciurumimus is a theropod dinosaur – part of the saurischian side of the family – it isn’t a coelurosaur. Sciurumimus is a megalosauroid, which is a lineage of dinosaurs that’s closer to the base of the theropod group. In other words, Sciurumimus is a relatively archaic theropod that isn’t very closely related to birds, yet it still has dinofuzz.

Paleontologist Thomas Holtz helped provide some context on Twitter shortly after the new dinosaur was announced. Before Sciurumimus, only coelurosaurs were known to have fuzz. (What the bristles on Psittacosaurus and Tianyulong actually are is still unclear, but no one calls their filaments “fuzz.”) After Sciurumimus, fuzz has been moved down a branch to a group called the Carnosauria.

We are still left with two possibilities. The fuzz on Sciurumimus could have originated independently. But as paleontologists add fuzz to lineages of dinosaurs only distantly-related to birds, it seems less and less likely that protofeathers evolved from scratch in each and every lineage. It’s looking more and more like feathers were a common, ancestral feature of dinosaurs. In this case, Sciurumimus indicates that simple feathers were an early, common theropod trait that evolved close to the origin of the group. The diminutive dinosaur also fits in the wide gap between coelurosaurs and their very distant ornithischian dinosaurs, bringing us a little closer to the idea that dinofuzz was an early, widely-shared dinosaur feature.

And there’s something else. Pterosaurs – the flying archosaurs with leathery wings stretched over elongated wing fingers – were the closest relatives to the Dinosauria as a whole. They had fuzzy body coverings, too. No one knows for sure, but this might mean that wispy plumage was present in the last common ancestor of dinosaurs and pterosaurs, and those simple body coverings were subsequently modified or lost in different lineages as both groups evolved.

We need more fossils to test the idea that dinosaurs started out feathery. Additional fossils preserving fuzz – fluffy baby sauropods, maybe? – would help us understand the spread of feathers and their precursors among dinosaurs. And, even then, we’d still need to find exceptionally-preserved specimens of the earliest dinosaurs to see if they had any kind of filament-like body covering. The trouble is that the high-definition deposits that would even have a chance of preserving feathers are rare. It may be a very long time before we ever know for sure.

Nevertheless, there’s still a possibility that all dinosaur lineages had some kind of bristly or feathery body covering. It’s a hypothesis that needs testing, but not an unreasonable one. Think about this for a moment. Imagine a Stegosaurus with patches of long, stiff filaments covering its body, or a Ceratosaurus with a little splash of brightly-covered fuzz on its already well-decorated head. And I think a huge sauropod – like Apatosaurus – with a partial covering of dinofuzz would look absolutely spectacular. These visions are wholly different than the scaly dinosaurs I grew up with, but they are not so fantastic as to be fiction. We are only just beginning to understand how fuzzy dinosaurs were.

For more on Sciurumimus, see my Nature News article and paleontologist Oliver Rauhut’s blog post about the discovery.

The skull of Yutyrannus. Photo by Zang Hailong.

Science is awesome. I know this because paleontologists have just announced the discovery of a giant, feather-covered tyrannosaur.

The freshly described dinosaur—dubbed Yutyrannus huali by Xu Xing and co-authors—stretched about 30 feet long as an adult. Thanks to the fine preservation of three skeletons that represent this roughly 125-million-year-old carnivore, we know that much of this dinosaur’s body was covered in fine, wispy feathers. These were not flight feathers or down that you might see on a modern bird, but simpler structures best described as dino-fuzz. This makes Yutyrannus the largest creature with observed plumage ever to have lived.

I have been waiting for Yutyrannus or something like it for a long time. The dinosaur is a beautiful confirmation of an evolutionary hypothesis made years ago. In 2004, Xu and collaborators described a much smaller tyrant: Dilong paradoxus, which lived only about five million years before Yutyrannus, was a small coelurosaur with a coat of simple fuzz. And Dilong appears to have been an archaic tyrannosauroid, a dinosaur near the base of the family that contained later tyrants such as Gorgosaurus and Teratophoneus. If a tyrannosauroid had feathers, and almost every other lineage closely related to the tyrannosauroids had feathers, then even Tyrannosaurus rex might have been at least partly coated in plumage.

Giant tyrannosaurs with feathers was a respectable idea, but there was no direct evidence. In North America, at least, tyrannosaurs were not entombed in the kind of environments with the high-fidelity preservation potential for feathers to make it into the fossil record. And, while they have frustratingly never been published, rumored specimens of tyrannosaur skin have hinted that adult animals had naked hides. Maybe tyrannosaur chicks were fluffy while adults, no longer needing an insulating coat, lost their feathers.

Not everyone has been on board with the idea of fluffy tyrannosaurs. The humor website Cracked.com listed an illustration of a feather-covered Tyrannosaurus one as of “17 Images That Will Ruin Your Childhood,” and the same image posted at BuzzFeed attracted more than a few negative responses. (“Dear god no!” wailed on commenter.) The smooth-skinned monsters of the Jurassic Park franchise remained the canonical pop culture image of everything a Tyrannosaurus should be.

A restoration of Yutyrannus , with the therizinosaurs Beipiaosaurus in the foreground, by Brian Choo. Caption added by the author.

I was ecstatic when news of Yutyrannus reached by inbox. Killjoy that I am, I loved the idea that the dinosaur made it all the more likely that other big tyrannosaurs were at least partly covered in filamentous protofeathers. I have no sympathy for immature attachment to traditional visions of scaly, drab tyrannosaurs. And, despite all the cries of “Ow! My childhood!” in reaction to feathered dinosaurs, Tyrannosaurus and kin would have been just as fearsome as ever. As tyrannosaur expert Thomas Holtz pointed out in a National Geographic news item, feathers “might make [Tyrannosaurus] a little more amusing, but only until the point right before it tears you to shreds.”

The extent of feathers on Yutyrannus and other tyrannosaurs isn’t entirely clear. Although I think Brian Choo’s illustrations of Yutyrannus are fantastic, and a full coat of fuzz is a fair hypothesis, patches of feathers were only found in a few places among the three specimens: the tail, hip, foot, neck and arm. That’s enough to hypothesize that much of the dinosaur was covered in feathers, but there’s always the possibility that non-avian dinosaurs had feathers on some parts of their bodies and not on others. Any restoration opting for either pattern is a hypothesis based on the available evidence.

Still, the discovery of any feathers at all means that we might find out what color Yutyrannus was. Microscopic studies of dinosaur feathers have helped establish the palettes of small feathered dinosaurs such as Anchiornis, Archaeopteryx and Microraptor. Now there’s the possibility of unlocking tyrannosaur colors, too. Was Yutyrannus mostly covered in dark plumage, like the other dinosaurs studied so far? Or did the tyrannosaur have a different color scheme? I guess we’ll have to wait and see—according to an interview with Xu on the Nature podcast, this research is already underway.

In spite of my overwhelming excitement about all this, though, there are two wrinkles in the story. The first is that there is a slight possibility that Yutyrannus may not actually be a tyrannosaur. As paleontologist Darren Naish points out at Tetrapod Zoology, Yutyrannus shows some subtle similarities to carcharodontosaurids, a subgroup of large predatory dinosaurs more closely related to Allosaurus. Exactly where Yutyrannus fits in the dinosaur family tree awaits confirmation by way of future analyses.

Should Yutyrannus turn out to be something other than a tyrannosauroid, that would immediately make the predator that much more important. At first, it seemed that only coelurosaurs—the group containing tyrannosauroids and sundry other theropod lineages, including birds—had feathers. Then paleontologists discovered feather-like structures on two very distantly related dinosaurs—the small ceratopsian Psittacosaurus and the diminutive, bipedal herbivore Tianyulong. (Following that, the carcharodontosaurid Concavenator supposedly showed evidence of bristles on its arms, but this evidence has been disputed.)

The spread of feathers and feather-like structures among dinosaurs might mean that secondary body coverings evolved at least twice on two different sides of the dinosaur family tree. Or it might indicate that simplified integument was a common trait shared among dinosaurs—a very old feature that was retained in some groups and lost in others. And here’s where Yutyrannus comes in. If Yutyrannus is not a coelurosaur but a carcharodontosaurid or something else, then it adds another feathery point in the dinosaur family tree and suggests that a wider array of dinosaurs had feather-like body coverings.

Yutyrannus isn’t even the only dinosaur that may shake things up. A smaller, earlier theropod called Juravenator was preserved with traces of dinofuzz, and there have been rumors that this dinosaur might turn out to be something other than a coelurosaur. Much remains to be established and tested, but the emerging picture is that several dinosaur lineages—very distantly related to birds—had secondary body coverings of one sort or another. It wouldn’t be altogether surprising if Yutyrannus turned out to be additional evidence of this trend. For now, though, the primary hypothesis is that Yutyrannus was an archaic form of tyrant dinosaur.

According to comments Xu made during a Nature podcast interview, the behavior of Yutyrannus may have made the predator even sexier still. The paper mentions three Yutyrannus individuals of different sizes, all found together. Other bonebeds of multiple tyrannosaurs have been used to propose that tyrant dinosaurs were highly coordinated pack hunters, and Xu follows suits with this discovery. Since the three predators were found together in the same quarry, and a sauropod skeleton has also turned up at the site, Xu says that the Yutyrannus were members of a pack that attacked the even bigger sauropod. For some unknown reason, all died together.

I’m not convinced that this was the case. Bonebeds are tricky things—there are many reasons why multiple skeletons may come to rest in the same place. The animals could have been forced into a relatively small area by flooding or storms, they could have died elsewhere and all been washed into the same place, or the site could have been some sort of predator trap. Very careful analysis of the geology and taphonomy of such sites is required to figure out why all those bodies wound up in the same place, and we shouldn’t take the association of skeletons at face value when trying to reconstruct dinosaur behavior. Could tyrannosaurs have hunted in groups? Certainly. But solid evidence for rapacious packs of big tyrannosaurs has yet to be found.

Alone or in coordinated social groups, though, Yutyrannus must have been a fantastic sight. Discoveries like this beautifully underscore just how wonderful dinosaurs really were. If previous discoveries hadn’t led us to expect the existence of this fuzzy dinosaurian hypercarnivore, I sincerely doubt that we could have imagined such a creature.

See also: Posts about Yutyrannus by Dave Hone and Ed Yong.

References:

Xu, X., Norell, M., Kuang, X., Wang, X., Zhao, Q., & Jia, C. (2004). Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids Nature, 431 (7009), 680-684 DOI: 10.1038/nature02855

Xu, X., Wang, K., Zhang, K., Ma, Q., Xing, L., Sullivan, C., Hu, D., Cheng, S., & Wang, S. (2012). A gigantic feathered dinosaur from the Lower Cretaceous of China Nature, 484 (7392), 92-95 DOI: 10.1038/nature10906