My Beloved Brontosaurus

by Brian Switek

  The damage on the Triceratops skulls was consistent with the idea that the animals often locked horns, and the pathology counts were significantly higher than the occurrence of lesions in the distantly related Centrosaurus. Within the sample of this dinosaur—an opposite of Triceratops, with a long nasal horn and short brow horns—a few individuals had lesions on their cheekbones, but the pattern of injury wasn’t the same. These dinosaurs were clearly doing something different. Indeed, Centrosaurus did not have a set of horns fit for interlocking, so, Farke and coauthors speculated, maybe these dinosaurs relied on visual displays while competing. This might in fact have been the predominant rule among ceratopsids. Ceratopsians had a fantastic variety of horn arrangements and frill shapes, many of which looked ill-suited for combat—either with rivals or with predators. In the recently described Kosmoceratops, for one, the short frill features a row of short horns folded over forward, and the dinosaur’s facial ornaments consist of two short horns jutting out sideways and a low, almost bladelike nasal horn. If these dinosaurs stabbed and battered each other with their heads, I have no idea how they did it.

  Indeed, many dinosaur ornaments probably had more to do with display than with defense. Dinosaur fashion was clearly focused on the bizarre: horns, spikes, plates, sails, and the like were common features, though each species wore them in a slightly different way. And for a long time, the purpose of much of this ornamentation seemed clear: the horns of Triceratops, the armor of Ankylosaurus, the domed head of Pachycephalosaurus, and the plates of Stegosaurus were defensive structures used to wound predators and, presumably, to win contests with rivals of the same species. But the way we think dinosaurs behaved is constrained by our imagination, or lack thereof. Just because an anatomical structure looks like a lance, a mace, or a battering ram doesn’t mean it was used as such. When scientists began to investigate the properties of the dinosaur arsenal, the difference between defensive weapon and display structure was obscured.

  Of all the dinosaurs with odd body structures, the thick-skulled pachycephalosaurs are among the most perplexing. These weren’t quadrupedal bruisers, but bipedal herbivores with domes of bone and accessory spikes on the tops of their heads. They seemed perfectly adapted for running headlong at each other and cracking skulls, much as bighorn sheep do today to determine dominance in their social groups.

  The most famous of all dome-heads, and the dinosaur from which the group derives its name, is Pachycephalosaurus itself. In profile, the dinosaur’s head was wedge-shaped, with a narrow nose decorated with bumps, an expanded and rounded skull ruff, and a series of bumpy ornaments around the back edge. Why any dinosaur should have such a head was a mystery, but, following the logic that bizarre structures were often for attack or defense, Edwin Colbert proposed that these dinosaurs frequently butted heads in competition. What else was a thick skull roof for?

  The pachycephalosaur-ram analogy was a rough one. The modern mammals have curved horns that contribute to a wide surface suited to absorbing shock. Pachycephalosaurus had a reinforced and rounded dome. When I visited the pachycephalosaur expert Mark Goodwin at Berkeley, I mused that contact between two such skulls would be like smacking two bowling balls into each other: all the force would be concentrated on one small area of contact where the domed surfaces met. “That’s right!” He laughed. If the dinosaurs ran at each other, they could fatally injure themselves.

  I wasn’t the first person to notice the drawback. Several paleontologists have suggested that pachycephalosaurs would have been rather poor head-butters, and Goodwin’s work with Jack Horner has underscored how lousy the structures were for going head-to-head. As the paleontologists found with other dinosaurs, the skulls changed dramatically as they aged, and the bone structure thought to make for good shock-absorbing powers was just a transitory state that disappeared before the animals reached full maturity. In Goodwin and Horner’s estimation, pachycephalosaur domes were probably signals to help members of a species recognize each other, and may have played a role in sexual competition and selection come mating season. The dinosaur “weapons” turned out to be social signals. Indeed, the weird ornaments among dinosaurs undoubtedly featured in their social lives, whether used for identifying members of their own species, for attracting mates, or for intimidating rivals. Of course, there were some cases—like Triceratops—where defense and display coincided, and a recently discovered fossil hints that this might have been true for Pachycephalosaurus, too.

  For years, critics of the head-butting pachycephalosaur idea noted that no one had ever found the kind of damage on these skulls that you’d expect if these dinosaurs were ramming each other. If the dinosaurs used their heads as weapons at all, they probably butted each other in the flanks. But in 2012, Joseph Peterson and Christopher Vittore identified a Pachycephalosaurus skull that had been injured by a traumatic impact and had suffered an infection following the incident. Peterson and Vittore concluded that head-butting behavior was the most probable explanation for the damage. As paleontologists look over their collections of pachycephalosaur skull domes, perhaps other examples will show up and fuel the ongoing oramentation debate.

  Pathologies like damaged frills and dented skull domes record fleeting interactions between dinosaurs, but the fact that the structures evolved at all can tell us something about dinosaur social lives. Horns, frills, domes, spikes, plates, and other features were multifunctional: they could be used for battle, and acted as visual signals, too. They were symbols that dinosaurs used to communicate, and, like bonebeds and tracksites, they offer us clues about how dinosaurs interacted with each other. Indeed, co-option is what evolution thrives on, and what a structure is currently used for doesn’t always reveal how that trait first evolved. Feathers are a perfect example. Even though many dinosaur ornaments were bony, feathers and their rudimentary, fuzzy precursors were a widespread dinosaur feature that undoubtedly played some role in dinosaur society. Indeed, even though plumage eventually allowed some dinosaurs to take to the skies, feathers originally evolved for other reasons related to display and insulation, and were only later repurposed for flight. Thanks to a fortuitous discovery, we can now start to understand how dinosaurs may have used color—even bright, gaudy color—to show off.

  Seven

  Dinosaur Feathers

  Sometimes I get a little selfish about dinosaur skeletons. As thrilled as I am that museum dinosaur exhibits are so well attended, the stampeding hordes of schoolchildren and waves of parents pushing their stroller-bound kids through narrow exhibit pathways can be more than a little agitating. Walking through dinosaur displays at peak hours requires serious agility to avoid the swarms of little ones buzzing around the place. And that’s not to mention the fact that few people seem to read the museum labels—any sharp-toothed predator is a Tyrannosaurus, and every supersized sauropod is a “Brontosaurus.” I want to butt in and point out the correct names, but when I’ve done so, I have often been met with annoyed glares. Better to keep my mouth shut and let the families enjoy their time in the midst of the fossilized superstars. “Be nice,” I have to remind myself, “… you’re just one of those irrepressible dinosaur fanatics all grown up.”

  I often watch the tide of visitors go by from the bench at the Natural History Museum of Utah’s paleontology lab. Behind a set of high glass windows, the other volunteers, technicians, and I go to work in a scientific fishbowl among tables stacked with fossils and covered in flecks of prehistoric rock. Sometimes I’ll be absorbed in my work—breaking off tiny pieces of sandstone from a fossil in the raw—and over the whine of the air-powered scribe I use to pick away at the encasing rock, I’ll hear a bang on the windowpane as a gaggle of kids catapults themselves onto the glass to get a better look. They’re so excited—until they realize that cleaning dead dinosaurs is a real pain in the ass, a war of millimeters between you and the matrix that surrounds the fossil bone.

  On some afternoons, when the flow of museum patrons has ebbed, I take a few minutes to amble throu
gh the exhibit halls. The quiet of the vast, dim space reminds me of my first trip to see New York City’s grand dinosaurs. The osteological galleries are among the few places where I can tune out the various distractions, always just a tap away on my smartphone, and let my mind drift as I walk past a pack of Allosaurus poised on tiptoe and gaze up to the ludicrously long neck of the museum’s titanic Barosaurus. I feel at home among the dinosaurs.

  And in those moments, I can’t help but wonder what the animals looked like when they were alive. Dinosaur skeletons are beautiful, exotic frameworks that supported flesh in life, and are the jumping-off point for my daydreams now. Fossil impressions of pebbly dinosaur skin fill in some of the details, but that’s just the canvas. Dinosaur color is another matter altogether. I can imagine sloshing buckets of polka-dot paint over the museum’s many-horned Utahceratops, but I doubt that in reality he would have looked so conspicuous. On the other hand, the traditional garb of drab green or gray isn’t very appealing, either. Maybe the horned dinosaur shared a palette with today’s African antelope, like the bongo—sienna shades set off with patches of black and thin white stripes. I can always revise the color scheme later.

  When I was a kid, books and museum displays told me that dinosaur color was one tantalizing aspect of Apatosaurus and company that we’d never be able to find out. The mystery was as frustrating as it was fascinating, and, from what I’ve heard, “What color were dinosaurs?” is still the question paleontologists field most often. For a long time, there was no answer. Whether working in paint or with the animatronic dinosaurs that terrified me the first time I saw them, artists could have free rein to pick any color scheme they wanted without fear of scientific reprisal.

  I used this to my advantage when I was still a young dinosaur fan and created a few dinosaur drawings for the paleontologist Peter Dodson. My father told me he was taking me to Dodson’s lecture at the local library, and I couldn’t wait. This was my chance to impress a real paleontologist! Someone who could open doors to fantastic collections and fossil-rich field sites! So I spent the afternoon sketching dinosaurs, including what turned out to be an atrocious drawing of the many-horned dinosaur Styracosaurus. This dinosaur had the same build as Triceratops, but with a vastly different head—a long nasal horn, short brow horns, and an array of intimidating spikes jutting backwards from its frill. And I honored this proud dinosaur by giving it a truly awful color scheme, too. The ceratopsid’s beak reminded me of a macaw, so I colored the dinosaur fire-engine red with a splash of white and black around the eye. I started with the eye first, and instantly regretted it. All the same, who could say? Later that night, I presented Dodson with the garish dinosaur. I’m forever grateful that he didn’t burst out laughing.

  That dinosaurs might have been so fantastically colored was a relatively new idea during my childhood in the 1980s, a concept that grew out of the notion that dinosaurs were more birdlike than anyone ever expected. Before that, dinosaurs traditionally wore stately, subdued colors. Olive green and mud brown were the default choices. Even movie dinosaurs, who were meant to be ferocious, vibrant creatures, had scaly hides duller than a pet-store lizard. The comically carnivorous “Brontosaurus” in King Kong (as well as the rest of Skull Island’s Mesozoic fauna, for that matter) flickered as gray monstrosities in weekend reruns of the film on my family’s television set, the grayscale colors a necessity of the early days of cinema. But dinosaurs in the age of color were lackluster, too. Ray Harryhausen’s anachronistic Triceratops and Ceratosaurus in 1966’s One Million Years B.C. wore uniform shades of brown and gray, and the brontosaur family of Baby: Secret of the Lost Legend were solid charcoal. Even Jurassic Park (which debuted two decades after artists and scientists took the colorful lessons of the Dinosaur Renaissance to heart) featured typically drab dinosaur stars. Apparently Steven Spielberg wanted classic Hollywood monsters rather than the most accurate dinosaurs science could offer. Jack Horner, who has been a paleontology consultant for blockbuster dinosaur films, once told me that the director drew a hard line on what the dinosaurs should look like, noting that Spielberg felt he couldn’t “scare people with Technicolor dinosaurs.”

  By the time Jurassic Park came out, the dull dinosaurs were behind the times. The realization that dinosaurs were extremely active, birdlike creatures opened a world of color possibilities to dinosaur artists. And some of those paleo-illustrators have had no trouble going overboard: think Deinonychus draped in neon colors, like a Cretaceous Cyndi Lauper. For the most part, though, artists turned to the natural world around them for some clues about dinosaur color. The paleoartist Gregory S. Paul, in his classic book Predatory Dinosaurs of the World, laid out a few rules for shading dinosaurs. “Since big living reptiles, birds, and mammals are never gaily colored like many small reptiles and birds,” Paul wrote, “one can assume that subdued colors were true of the big predatory dinosaurs, also, which to human sensibilities gives them a dignified air appropriate to their dimensions and power.” Stripes, spots, or patches of iridescent color around the snout are acceptable, Paul said, but duller color schemes are the most practical.

  But dinosaur color is no longer strictly the realm of speculation and artistic taste. Living dinosaurs, as well as fossils bearing impressive plumage, have provided an unprecedented window into prehistory. The key to the whole puzzle is a simple, beautiful fact that has irrevocably changed the way we look at dinosaur lives. It is simply this: birds are dinosaurs. It’s a strange notion to think that the little hummingbirds that come to sip from the feeder planted just outside my window are part of the sole surviving dinosaur lineage, but there’s no doubt about it: the Age of Dinosaurs continues. Birds just so happened to be the one dinosaur lineage that survived the end-Cretaceous extinction. It took more than a century for scientists to agree on this point, and it’s worth taking a moment to consider the long history of the debate and how it relates to what our extinct dinosaur friends looked like.

  There has always been one critical fossil that comes up in the discussions paleontologists have about the origins of birds: Archaeopteryx. Described in 1861 from a feather and a partial, feathery skeleton discovered in a German limestone quarry, this mosaic of reptilian and avian traits has been the keystone for varying theories about how birds originated. Lately, a slew of dinosaurs with plumage has led paleontologists to question what Archaeopteryx really was.

  * * *

  I remember exactly where I was when Archaeopteryx was threatened with demotion from its place as an evolutionary icon. I was sitting at an Exxon station in the middle of nowhere Montana, waiting for my rented SUV to finish fueling so I could continue my journey from the isolated town of Ekalaka (where I had been looking for dinosaurs with the paleontologists Thomas Carr and Scott Williams and their field crews) down to Thermopolis, Wyoming. After running into the convenience store to buy the requisite snacks and caffeine for my seven-hour trip, I checked my messages to see if I had missed anything important while I was in the field. New dinosaur studies come out faster than you might imagine.

  E-mails trickled into my inbox. Mostly junk. But then there was a spate of messages from the ever-prolific Dinosaur Mailing List, titled “Greg Paul is right (again); or ‘Archie’s not a birdy.’” The title referred to an idea, suggested years ago by paleoartist Paul and others, that Archaeopteryx was not the earliest known bird, but in fact one of a variety of feather-covered dinosaurs more closely related to the famous predators Deinonychus and Velociraptor. The idea had been kicked around over the years without much enthusiasm, but a paper in Nature had been released that afternoon which shook up the bird family tree and punted Archaeopteryx off to the non-avian dinosaur branch.

  I cursed my luck that I couldn’t get the report at my roadside stop, but since I was the only one at the pumps, I didn’t feel bad about taking a few extra minutes to see what news services were saying about the theory. If there’s anything reporters love more than a story about Tyrannosaurus rex, it’s a story claiming that some facet of dinosa
uriana we had taken for granted has turned out to be wrong.

  The splash of articles on the study didn’t disappoint. “‘Oldest bird’ Archaeopteryx knocked off its perch in controversial new study,” said one. Another baited evolution denialists with the title “Newly discovered dinosaur could disprove ‘earliest bird’ theory,” although the article itself only stumbled through a litany of tidbits about Archie and a new feathered dinosaur dubbed Xiaotingia.

  Apparently, after analyzing the evolutionary relationships of Xiaotingia, the paleontologist Xu Xing and colleagues found that both Xiaotingia and Archaeopteryx were more closely related to feathered but non-avian dinosaurs like Velociraptor. Bizarre, poorly understood forms such as Epidexipteryx—a small theropod decorated with ribbon-like feathers, with a mouth full of procumbent teeth—fell out closer to the ancestry of birds in this new evolutionary tree.

  Depending on how you look at it, this was either a case of the best or worst possible timing. The entire reason I was on the road to Thermopolis—a tiny dot in the middle of Wyoming, best known for its hot springs—was to see the only Archaeopteryx specimen in the United States. If the report held true, the urvogel (original bird) had been cast down just a few hours before I was due to roll into town. “You’ve got to be kidding me,” I thought as I pulled out of Exxon and started my long interstate drive.