by Brian Switek
Microraptor is one of more than thirty feathered non-avian dinosaurs found so far. (The white arrows point to feathers on this dinosaur, and the black arrows indicate more subtle feather traces that can be seen only under UV light.) By studying the microscopic structure of Microraptor feathers, paleontologists have even discovered that this dinosaur had dark, glossy feathers. In life, it looked something like a toothy raven. (Image from www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0009223)
At least thirty different feathery non-avian dinosaurs have been recognized since that first one. Some are more “birdlike” than others. Anchiornis—a roughly 160-million-year-old, pigeon-size dinosaur—had elongated feathers on its arms and legs that might represent an intermediate state between wholly terrestrial dinosaurs and early fliers. And even Velociraptor, a turkey-size predator that most certainly did not fly, had elongated feathers on its arms—a feature inferred from quill knobs preserved on the dinosaur’s arm bones. If there is ever a Jurassic Park 4, and that movie has Velociraptor reprise its role, the dinosaur should sport some exquisite plumage, Steven Spielberg’s sense of taste be damned.
Even bizarre dinosaurs further removed from the avian rootstock sported decorative, feather-like structures. Beipiaosaurus inexpectus—a potbellied dinosaur with long claws, an extended neck, and a beaked skull better suited to clipping plants than slicing flesh—was enveloped in two layers of differentiated, simplified, elongated feathers. Tyrannosaurs had feathers, too. A small form named Dilong and a much more formidable, 30-foot genus called Yutyrannus had filamentous coats of fuzz. Thanks to these finds, we can say that Tyrannosaurus rex was probably a feathery giant—an idea that will undoubtedly cause dinosaur traditionalists to have a conniption.
Feathers were not just a feature of birds and their closest non-avian predecessors. Birds are just one lineage of a wider theropod family called the Coelurosauria. Every lineage within the Coelurosauria has at least one representative with dinofuzz or full-blown feathers. More than that, we now know that feathery adornments were a common dinosaur feature. Two dinosaurs—each about as far removed from birds as possible—also displayed body coverings structurally very similar to simple feathers. Psittacosaurus, which looks like an animal with a parrot head and a ceratopsian body, had an array of bristles along its tail. Even though most of its body was covered in scales, the bristles were very similar to the fluffy coatings found on theropod dinosaurs. And another dinosaur named Tianyulong sported a row of similar bristly ornaments along its back. These dinosaurs were ornithischians—forms that existed on the other side of the evolutionary tree from the coelurosaurs. Since creatures on both sides of the dinosaur family tree had feathers or feather-like body coverings, the fuzz and bristles might have been a common dinosaur feature, inherited from the last common ancestor of all dinosaurs. And the description of a fuzzy juvenile dinosaur named Sciurumimus in 2012—a dinosaur near the base of the theropod family tree, far from birds—added another feathery data point to the idea that protofeathers were widespread among dinosaurs. Most, if not all, dinosaur lineages might have had dinofuzz, and that includes the impressive sauropods. (Just think of how cute a fuzzy little Apatosaurus juvenile would be.)
Thanks to exquisitely preserved skeletons with intact gut contents, we know that fuzzy dinosaurs such as Sinocalliopteryx fed on their feathery neighbors, including other non-avian dinosaurs (left) and early birds (right). (Art by Cheung Chung Tat. Image from www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0044012)
Even though there isn’t any direct evidence yet, the discovery that many dinosaurs were partially covered in protofeathers means that some sauropods—such as this juvenile Apatosaurus—might have been fuzzy, too. (Art by Niroot Puttapipat)
We are left with only two possibilities. Either the same kind of simple filaments evolved over and over again, or dinofuzz was an ancient trait that was present in all dinosaur lineages. I can almost hear the scaly-tyrannosaur fans weeping.
Even Tyrannosaurus rex itself was probably coated in fuzz. Despite complaints from fans of scaly T. rex, the carnivore wouldn’t have been any less fierce. (Art by Niroot Puttapipat)
The various types of prehistoric feathers cataloged so far outline how plumage has evolved. As far as paleontologists understand as of this writing, feathers started off as fuzz and in time were adapted into complex structures that allowed some dinosaurs to take to the air. Protofeathers were simple, single filaments. These are the kinds of structures seen on the bodies of Psittacosaurus, Tianyulong, and Sciurumimus. Archaic coelurosaurs—agile little dinosaurs like Sinosauropteryx, the first to be recognized with dinofuzz—had slightly more complex coats. Their protofeathers had multiple branches coming out of a central filament. These feathers were not all that different from those seen on oviraptorosaurs—beaked, omnivorous dinosaurs that were already quite birdlike to start with—as well as on parts of some true early birds. (Some feathered dinosaurs and early avians had multiple feather types on their bodies, just like modern birds.)
In the next stage of feather evolution, the individual filaments branched further along a central support. In dinosaurs such as Microraptor as well as in the earliest birds themselves, these individual filaments eventually formed true leaf-shaped feathers organized along a central vane. Some of these feathers, like those seen in the flightless raptors, couldn’t support dinosaurs in the air, but flying dinosaurs—including Archaeopteryx and the four-winged Microraptor—had specialized, more aerodynamic feathers that were thinner along the leading edge. These were the feathers that finally allowed dinosaurs to invade the skies. Feathers originally formed insulating coats and flashy displays, and at least one lineage co-opted the same structures to become the only flying dinosaurs. Regardless of what Archaeopteryx was or was not, the gradual flow of scientific discoveries has revealed dinosaurs as increasingly birdlike and inextricably connected avian dinosaurs to their non-avian forerunners. Fossil feathers solved the mystery.
There’s more to the dinosaur-bird connection than avian origins alone. Many of the fantastic new discoveries about dinosaur biology have been influenced by the fact that we have living dinosaurs to study. A chickadee isn’t an Ankylosaurus, and an emu isn’t a Diplodocus, but today’s birds can help paleontologists refine questions and ideas about how dinosaurs lived. Best of all, our avian dinosaurs can finally help us fill out the palette of their extinct relatives.
As Charles Darwin wrote, “[I]gnorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science.” Darwin was referring to humanity’s origin—a mystery complicated by elusive evidence and dogmatic religious strictures—yet the same argument applies to the question of dinosaur colors. The problem was not an absolute lack of evidence, but the fact that the stepwise process of scientific understanding has only very recently grasped where to look for the essential clues.
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I was reminded of Darwin’s line while waiting for a session to start at the Society of Vertebrate Paleontology’s 2011 meeting in Las Vegas—quite a setting for a conference on prehistoric life. The constant lights and buzz of Bally’s grated on my every nerve, but I tolerated the cigar-smoking gamblers and the bagpiper who played on the street below until the early hours of the morning, because this was the temporary haven for the best and most cutting-edge info on paleontology. I had been waiting all year to hear about the new discoveries being made in the field and the lab. I especially wanted to hear what Brown University graduate student Ryan Carney had to say: he was set to reveal the true color of the first Archaeopteryx specimen ever found—the isolated feather used to name the dinosaur 150 years earlier.
The paleoartist Bob Walters sat down to my left a few minutes before the presentation was scheduled to start, notepad at the ready. I jokingly asked if he was angry at paleontologists who stepped on his turf and told him what colors were now conside
red acceptable. Bob looked shocked. “Not at all!” he said. Artists like Bob had long been hoping for some scientific indication of dinosaur color, he said, and now paleontologists were going to give them just that.
Once Carney took the stage, he didn’t waste any time relaying the news of his team’s discovery. The Archaeopteryx feather was black. Whether the whole animal was black was impossible to say. The single feather was selected because it was a famous specimen and it was the sesquicentennial anniversary of when the beloved feathered dinosaur was named, but nevertheless, the analysis had finally attached a color to one of the world’s most important fossils.
The method by which Carney and his collaborators determined the dinosaur’s hue was developed several years ago, and it all started with a squid. A very, very old squid, but a squid all the same. Jakob Vinther, a molecular paleobiology graduate student at Yale University, was inspecting the ink sacs of a fossil cephalopod under a high-powered electron microscope when he noticed little blobs inside the membranous pocket. Paleontologists had seen structures like these before and had assumed that they were fossilized bacteria, locked in stone as they started to break down prehistoric soft tissues. But the fact that the microscopic spheres were restricted to the inside of the ink sac suggested something different. These were melanosomes—tiny organelles whose shape, density, and distribution create pigment. In the squid, the melanosomes gave a dark-brown color to the ink the cephalopod used to escape from predators, and Vinther wondered if melanosomes might be detected in other fossils.
Feathers seemed a good place to look because many of their colors are created by melanosomes. If fossil feathers contained melanosomes, and zoologists could examine the feathers of modern birds to see how the organelles corresponded to certain colors, then they could reconstruct the colors of prehistoric creatures. Before Vinther and his collaborators could investigate non-avian dinosaur feathers, they had to establish that they were really seeing melanosomes and not bacteria. They did just that with a fossil feather from Cretaceous Brazil. The feather was banded white and black. If the little round bodies were bacteria, then they should have been found all over the feather’s surface. As the researchers discovered, though, the tiny spheres were constrained to the dark sections only. These were the bands that would have carried pigment, and so the scientists could be confident that they had identified real melanosomes.
Vinther knew that the findings had applications for dinosaurs, too. A beaked, birdlike dinosaur named Caudipteryx, he and his team pointed out, had a fan of banded tail feathers that might actually represent the true color pattern of the dinosaur. But his study didn’t catch the public’s attention. This was 2008. The key to dinosaur color had just been found, and yet the implications didn’t reach far beyond the small number of researchers who read the paper. Still, the scientists kept at it, and the following year, Vinther led another study on a 47-million-year-old feather found in Germany. This one, from a bird that lived about eighteen million years after the demise of the last non-avian dinosaurs, had an iridescent sheen in life.
Non-avian dinosaurs were next on Vinther’s list. But as often happens in paleontology, another team got there first. On January 27, 2010, the Chinese Academy of Sciences paleontologist Zhang Fucheng and a team of collaborators published online a letter in Nature about the colors of Cretaceous birds and, for the first time, non-avian dinosaurs. Among other specimens, the team had selected a Sinosauropteryx—the fuzzy dinosaur that had marked the onset of a flood of feathered dinosaurs from China starting in 1996. From the time the dinosaur was described, it was apparent that the protofeathers along its tail had a banded pattern. The team took only a very limited sample, but concluded that the darker patches had been reddish-brown. Sinosauropteryx had a candy-cane tail that could have been used as a visual signal among these dinosaurs.
A week after the online announcement, Vinther’s team countered with an even more detailed study in Science. It was the first time a non-avian dinosaur had been fully restored in color. The Beijing Museum of Natural History paleontologist Quanguo Li, Vinther, and collaborators worked with a specimen of Anchiornis. This small dinosaur was known from multiple, roughly 160-million-year-old specimens, and it looked something like a magpie. Anchiornis was black with swaths of white on its arm and leg feathers. But most impressive of all was a tuft of reddish plumage on the dinosaur’s head. I hadn’t seen anything like it before. Anchiornis looked rather plain, but in a strikingly beautiful way, made all the more wonderful by the fact that we could now tell what color dinosaurs were.
Both Archaeopteryx and Anchiornis were at least partly covered in black feathers. They looked like modern crows rather than birds of paradise. Vinther and colleagues found similar hues when they looked at the feathered dinosaur Microraptor. Using the same techniques on an absolutely gorgeous specimen of this sickle-clawed dinosaur, the team discovered that it boasted a glossy coat of complex feathers. Like Anchiornis and Archaeopteryx, Microraptor was a dark-colored dinosaur which wouldn’t look out of place perching with the ravens along a western highway.
It never ceases to amaze me that we can now tease out dinosaur colors from the fossil record. The implications go far beyond the artist’s palette choices. Whether stripes, spots, or iridescent plumage, feathered dinosaurs boasted visually arresting patterns. These dinosaurs were highly visual creatures who communicated with lovely, colorful displays. Even better, as we study more specimens from each species, we’ll be able to investigate whether dinosaurs had different color patterns in each sex or distinct breeding plumage. Color might be the key to other aspects of dinosaur biology.
So far, the technique works only for dinosaurs with preserved feathers. For species of dinosaur that didn’t have feathers, or even specimens of feathered species that were preserved without their plumage, we can’t investigate their colors. We’re also still looking for a way to detect and restore chemically created colors—some of the greens, blues, oranges, and yellows seen in many birds. As far as the science can reach, at least at the moment, there needs to be something to preserve the melanosomes and to be compared to modern analogs. You can’t draw blood from stone, but if you know how to look, you can get dinosaur colors.
We’re fleshing out the old bones that pack museums around the globe. We’ve uncovered intricately preserved specimens, reconstructed their body coverings, and now have a good sense of what they looked like. So with all of this in mind, how did dinosaurs see each other? Birds can see ultraviolet parts of the spectrum—could Microraptor have exchanged visual cues that we could never hope to see? What if there were a way to get inside a dinosaur’s head, see the world through her eyes, and understand how she perceived her surroundings?
Eight
Hadrosaur Harmonics and Tyrannosaur Tastes
What is a dinosaur without a roar? From awkward, jerking robots in traveling museum exhibits to the best special effects Hollywood can muster, the ability to thunder an ear-shattering, gut-shaking primal scream is what brings dinosaurs to life. Unknown Island—the 1948 stinker that was the first to show rampaging dinosaurs in color—wouldn’t have been the same without the chaotic cacophony of Ceratosaurus screeches, and Jurassic Park wouldn’t have seemed so dangerous without the terrifying bluster of Tyrannosaurus. And it’s not just the carnivores. Imposing herbivores like Triceratops, Brachiosaurus, and Ankylosaurus come to life through their hoots, snorts, and snuffles, too. Even in Discovery’s docudrama Dinosaur Revolution, dinosaurs are all about grunting and snarling their archosaurian hearts out. If cinema and basic-cable documentaries are to be believed, dinosaurs were some of the chattiest creatures of all time.
Like many intricate details of dinosaur lives we see on screen, these distinctive sounds are speculative. Dinosaur noises in pop culture are often composed from various animal sounds spun together in a blender. The bone-rattling roar of Tyrannosaurus in Jurassic Park is actually a combination of elephant, alligator, tiger, dog, and penguin sounds. I learned early on in elementary school
art class that mixing enough colors made brown, and it would seem that if you blend enough animal noises together you ultimately get a dinosaur bellow.
Far too much time spent in front of flickering screens taught me that dinosaurs must have had impressive voices to match their imposing frames, but I have always wondered what they really sounded like. The Fayetteville State University paleontologist Phil Senter has pondered the same question in his paper “Voices of the Past: A Review of Paleozoic and Mesozoic Animal Sounds.” I hoped Senter had had access to both prehistoric dinosaurs and a high-fidelity recording device. Sadly, this wasn’t the case, and as he reminds readers, “The fossil record does not include audio recordings.” Damn.
Lacking direct access to dinosaur sounds, Senter resorted to the tried-and-true method of using modern animals to investigate what prehistoric creatures might have sounded like. In the case of the dinosaurian multitude, of course, this meant turning to crocodylians and avian dinosaurs for clues. The trouble is that the two archosaur groups don’t produce sound in the same way. While crocodylians vocalize through their larynx, birds sing and chirp via a different organ, called the syrinx—a series of cartilage rings deeper down in the upper respiratory tract. Since these structures are so different, Senter argued, the sound-producing abilities of crocs and birds must have evolved independently of each other. Therefore, Senter concluded, dinosaurs probably didn’t scream, sing, or roar. As a consolation, he proposed that dinosaurs made sounds by other means—hissing, clapping their jaws together, rubbing their scales, splish-splashing in the water, and, for Apatosaurus and similarly equipped sauropods, cracking their whiplike tails. That’s not especially satisfying to someone raised on especially vocal Tyrannosaurus and Triceratops.
I hadn’t considered all the different ways dinosaurs could have made sounds. When rival Spinosaurus met on ancient floodplains, did they clap their crocodile-like jaws to threaten each other? Did a mother Oviraptor hiss at intruders who ambled too close to her nest? Scenarios like these are certainly possible, but I still believe that dinosaurs had voices, too. After all, even though living dinosaurs—birds—and the closest living cousins of dinosaurs—crocodylians—vocalize differently, their common ancestor wasn’t necessarily mute. Birds still have a larynx, even though they don’t use it to make sounds, and crocodylians are vocal enough via the same structure. Perhaps most non-avian dinosaurs had a more croc-like mode of expressing themselves before the specializations that allow birds to sing evolved. When I visited some baby alligators in their rooftop greenhouse at the University of Utah, I mostly heard hisses—the sharp-toothed babies were not very happy that I had stopped in. But take just a few minutes with YouTube and you’ll find that you can sample a few other crocodylian noises too. Take the short clip of a male American alligator at the St. Augustine Alligator Farm Zoological Park. The alligator’s rumble sounds like a cross between a clogged drain that’s suddenly unstuck and a failed attempt to start a lawn mower. Another clip, filmed in the Everglades National Park, shows a pair of males—heads raised, tails lifted high out of the water—making similar noises in territorial displays. The water dances over their armor-covered backs as they call to each other.