My Beloved Brontosaurus

by Brian Switek

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  In order to appreciate how our understanding of dinosaurs has changed, though, we need to know what dinosaurs really are. That’s not as simple as it sounds. Here’s what dinosaurs are not: they are not just anything big, toothy, and prehistoric. A woolly mammoth wasn’t a dinosaur, the leathery-winged flying reptiles called pterosaurs weren’t dinosaurs, and fish-chasing aquatic reptiles such as the plesiosaurs and ichthyosaurs weren’t dinosaurs. Just because an animal’s name ends in “saur” doesn’t necessarily mean it’s a dinosaur. “Dinosaur” is a scientific term, not a colloquial one, and applies only to a restricted group of animals.

  The simplest way to visualize this is by picking two of the last members of each branch of the dinosaur family tree and tying them back to their last common ancestor. So if you were to take Triceratops and a pigeon (birds are dinosaurs, too) and go back to their last common ancestor, everything that rests within the resulting evolutionary tree would count as a dinosaur, all of them bound together by a mosaic of shared anatomical features. If an animal doesn’t fall within those brackets, it’s not a dinosaur. That’s a strange way to think of delimiting dinosaurian identity, but the proof is in their evolutionary relationships.

  Let’s dig a little deeper. The reason we pick Triceratops and a pigeon to outline the dinosaur family tree is because these animals represent the ultimate members of the two major dinosaur subgroups. The dyspeptic Victorian anatomist Harry Govier Seeley delineated these varieties in 1887 on the basis of dinosaur hips, of all things. While some dinosaurs (such as Allosaurus and Apatosaurus) had roughly lizard-shaped hips, others (such as Stegosaurus) had what Seeley thought were bird-like hips. He named the two varieties the Saurischia and Ornithischia, respectively (even though the latter name turned out to be ironic—although birds are dinosaurs, so-called bird-hipped ornithischian dinosaurs weren’t anywhere close to avian ancestry).

  While the names don’t exactly roll off the tongue, Ornithischia and Saurischia are essential labels for understanding who’s who among the dinosaurs. All the dinosaurs we know of fall into one group or the other. The myriad of bizarre dinosaur forms is staggering. Among the Ornithischians were dome-heads like Pachycephalosaurus; shovel-beaked hadrosaurs such as the crested form Parasaurolophus; armored dinosaurs such as Ankylosaurus; and Pentaceratops—a massive quadruped with curved brow horns and a flashy, elongated frill. As far as we know, all of these dinosaurs were principally herbivorous.

  The Saurischia, on the other hand, includes some of the largest, fiercest, and most charismatic dinosaurs of all. The two principal saurischian subgroups were the sauropodomorphs—long-necked herbivores that included Apatosaurus and its close kin—and the theropods. For a long time, “theropod” was synonymous with “carnivorous dinosaur,” but that isn’t true anymore. Tyrannosaurus, Allosaurus, and Giganotosaurus were all flesh-rending theropods, as were Velociraptor and its kin, but many theropod lineages became either omnivores or herbivores, and those include birds. While the carnivores have traditionally stolen the show, the weirdest theropods belong to recently discovered groups such as the alvarezsaurs—turkey-size dinosaurs thought to be the Mesozoic equivalent of anteaters—and potbellied feathery herbivorous dinosaurs with insanely long hand claws, called therizinosaurs.

  Our understanding of just how wildly divergent dinosaur body plans were is constantly changing. The word “dinosaur” technically includes everything from an Emperor penguin to one-hundred-foot behemoths such as Supersaurus, heavy-skulled bonecrushers like Tyrannosaurus, and spiky, armor-plated enigmas such as Stegosaurus. We probably don’t even know the full span of dinosaur body types. Within the past three decades alone, paleontologists have identified several kinds of dinosaurs that we had no conception of before. The ant-eating alavarezsaurs and totally weird therizinosaurs are two such groups, but there are also the abelisaurids—theropods with short, deep skulls and wimpy arms that even a tyrannosaur would laugh at—and croc-snouted, sail-backed carnivores called spinosaurs.

  And that’s to say nothing of the dinosaurs that lived after the mass extinction that closed off the Cretaceous, about 66 million years ago. Dinosaurs were not exclusively prehistoric animals—we now know that birds are the sole surviving dinosaur lineage. Indeed, birds are dinosaurs, but the majority of forms—the types that most immediately spring to mind when you think of the word “dinosaur”—are called non-avian dinosaurs. Many writers and paleontologists prefer to consider “non-avian dinosaur” and plain old “dinosaur” as synonyms because of the cumbersome jargon, but I think it’s about time we came to terms with the technical language. Yes, it can be a little unwieldy, but we insult dinosaurs if we ignore the fact that they are still with us.

  To most people, “dinosaur” is something extinct. And recent discoveries—such as the spinosaurs and alvarezsaurs—are showing us how much there is left to be uncovered. Many of these discoveries have come from sites in South America, Africa, and Asia that were beyond the reach of early fossil hunters, but even North America and Europe—the continents that have been systematically sampled for the longest time—have yielded strange dinosaurs unlike anything anyone has seen before.

  All these fossil finds come from a distinct swath of prehistoric time. The Mesozoic span of the dinosaurs ran for more than 160 million years the world over. The dinosaurian heyday fell across three different geological periods—the Triassic (250 to 200 million years ago), the Jurassic (199 to 145 million years ago), and the Cretaceous (144 to 66 million years ago). That is a lot of time for evolution to usher new forms into existence. Even though we may never find all the dinosaur species, as some probably lived in habitats where there wasn’t the right combination of factors for fossilization, there are certainly thousands of as-yet-unknown dinosaurs waiting to be found.

  Dinosaurs aren’t only prehistoric animals, real monsters, or even objects of scientific scrutiny. They’re icons and cultural celebrities. As the journalist John Noble Wilford wrote in The Riddle of the Dinosaur, “Dinosaurs, more than other fossils, are public property, creatures as much of the public imagination as of scientific resurrection.” Dinosaurs invade our music, our movies, our advertising, and our idioms (although “going the way of the dinosaur” should really mean becoming undeniably awesome, rather than sinking into inevitable extinction). NASA even shot dinosaurs into space twice. Don’t ask me what for, but they transported dinosaur fossils into space all the same—maybe because the creatures have so utterly entranced us and there’s hardly a higher honor for our favorite monsters than for their bones to be granted a cherished place on a trip outside our atmosphere.

  With dinosaurs everywhere, it’s no surprise that going through a “dinosaur phase” is a common and almost expected part of American culture. There’s something about these creatures that has an immediate and inextricable appeal to children, and more than a few young dinosaur fans hold on to that passion to become paleontologists. I’ve never heard a good explanation for why this is. I don’t buy the pop-psychology logic that dinosaurs are so celebrated because they are animals that are big and fierce, but safe because they’re extinct. The appeal of dinosaurs doesn’t just lie in our ability to conjure them up and banish them at will. There’s something else at work, embedded in our curiosity about where we fit in the history of the world.

  Indeed, dinosaurs fueled rampant speculation about history and our place in it even before they had a name. From the Greeks to Native Americans, ancient cultures and aboriginal people concocted legends of hoary terrors and powerful heroes to explain the unusual animal bones they found crumbling out of the earth’s crust, and the first English naturalists to describe dinosaurs saw them as fearsome, sharp-toothed reptiles of untold destructive power. Their remains were so strange and frightening that we instantly recognized they were primordial beasts that vanished long ago. More than anything else, the attractive essence of the dinosaurs lies in their bizarre and terrifying nature. We can’t help wonder about creatures that, from the very start, we’
ve envisioned as Tennyson’s “Dragons of the prime, / That tare each other in their slime.”

  Those images of dinosaurs easily become entrenched in our minds, even as science continues to revise what we thought we knew about them.

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  Our understanding starts with finding the dinosaurs themselves. We can’t begin to reconstruct the identity of dinosaurs, and the details of their lives, without first collecting their bones.

  I thought about this undeniable fact, and the romance of fossil discovery, in 2011 as I stood on the balcony overlooking Douglass’s old quarry, now cleaned and dusted to show off the mass graveyard in detailed relief. This is the heart of Dinosaur National Monument, and the crowded graveyard exemplifies the very beginning of our struggle to reconstruct dinosaur biology. The vista is the result of countless hours of work. For years, experts picked away at the rock face to expose the bones right in front of museum visitors.

  A view of life in Jurassic Utah, 150 million years ago. This was the habitat of Apatosaurus—the bulky sauropod seen crossing the floodplain at center. (Art by Robert Walters and Tess Kissinger, courtesy of Dinosaur National Monument, Utah)

  Today, the work has stopped. Almost everything there is to find has been uncovered, and I’m a little disappointed that I can’t watch the diligent fossil excavators go about their work (or even have a crack at carefully chipping out a few bones myself). Finding and digging dinosaurs is grueling, sweat-drenching work, punctuated by brief periods of excitement. When I’m in a quarry, in the lab, or in the field looking for dinosaurs in the rough, uncovering a fossil is an exhilarating experience—when my eyes settle on a freshly exposed bone or fragment, I can’t help but wonder what sort of animal it belonged to and where it fit in the organism’s skeleton. As George Gaylord Simpson, one of the greatest paleontologists of the twentieth century, once wrote:

  Fossil hunting is far the most fascinating of all sports. I speak for myself, although I do not see how any true sportsman could fail to agree with me if he had tried bone digging. It has some danger, enough to give it zest … and the danger is wholly to the hunter. It has uncertainty and excitement and all the thrills of gambling with none of its vicious features. The hunter never knows what his bag may be, perhaps nothing, perhaps a creature never before seen by human eyes. Over the next hill may lie a great discovery!… The fossil hunter does not kill; he resurrects. And the result of his sport is to add to the sum of human pleasure and to the treasures of human knowledge.

  That same spirit is what led Earl Douglass to devote his life to uncovering his great Jurassic bonebed, and this romance fueled the institutional “My dinosaur is bigger than yours” contest that yielded splendid reconstructions of Apatosaurus—née “Brontosaurus”—in the exquisite museum halls of Pittsburgh, Chicago, and New York City. Those fantastic displays, like those all over the world, were petrified trophy rooms that showed off what toiling in the badlands might teach us about prehistory and our place in nature. The delicately mounted skeletons speak of a past so far beyond the reach of human memory that we can’t even fully comprehend the depth of that time, and their stock-still skeletons place our own existence in context. (Consider this: Tyrannosaurus lived closer to us in time—66 million years ago—than it did to Apatosaurus, which lived 84 million years prior.) Indeed, although Douglass’s dinosaurs gave his quarry its fame and eventual protection as a museum, the teeth and bones of tiny mammals are needles in this dinosaurian haystack. Our ancestors and cousins snuffled through the undergrowth and hid in the darkness of the Jurassic world, without so much as an inkling that the seemingly indomitable reign of the dinosaurs would someday end.

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  As fun as fieldwork can be, though, paleontology is far more than a trophy hunt. Finding a dinosaur is only the very start, and the little secret of fossil hunters is that if you pick the right geological setting, and can tell bone from rock, it’s not all that hard to find dinosaurs. The exercise relies almost as much on luck as on science. And, after finding a few myself, I discovered that uncovering a dinosaur bone doesn’t feel quite the way it’s so often portrayed on television. In the endless stream of dinosaur documentaries I watched growing up, a paleontologist would often rhapsodize about being the first pair of eyes to see the freshly uncovered dinosaur bones in 66 million years or more. The scientists were apparently enthused just by the success of the hunt.

  But that’s not what I thought about as I carefully scraped the sediment off a dinosaur femur in Ghost Ranch, New Mexico; when I plucked up a handful of dinosaur teeth in the ranchlands outside of Ekalaka, Montana; or even when I stared at Dinosaur National Monument’s beautiful Jurassic cemetery. Dinosaur fossils are vestiges of ancient life. So many questions can be asked of even a single bone: how the dinosaur moved, what colors adorned its skin (or feathers), what the creature ate, how it died, and where it fit in the wider panorama of life on Earth, just to start. That’s the passion of paleontology. Dinosaurs are old, yes, but they are also mind-bogglingly strange. The persistent questions about how such creatures could have evolved and thrived for so long are what drive me, and many other dinosaur fans, to keep digging into their history. And this is not just a dry academic exercise. This is personal. If I can uncover the secrets of their evolutionary success, maybe I can start to comprehend my endless fascination with them.

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  I had so many questions as a child that I was told we’d never answer. Slowly, and amazingly, we’re starting to envision dinosaurs as they truly were. Paleontologists are painting a more intimate portrait of dinosaurs than has ever been composed before. The days of headhunting for prize skeletons and then leaving those bones to collect dust on museum shelves are over. The bones now form the basis of intense research programs that probe, scan, and dissect the fossil remains for whatever clues we can find about the lifestyles of the fierce and extinct. The Dinosaur Renaissance drastically changed dinosaur imagery, but, as the University of Maryland paleontologist Thomas Holtz once told me, it’s the new Dinosaur Enlightenment that is outlining the details of how the animals lived.

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  Science is not just the stepwise accrual of facts that are written down and then forgotten. Fact and theory are intertwined, fostering our ever-changing perception of nature. The more we learn about dinosaurs, the stranger they become and the more questions we have about their biology. And the mystery of the dinosaur is wrapped up in two complementary themes—how they lived and why almost all of them disappeared. In order to solve those conundrums, we need to solve a slew of other dinosaur mysteries—how they mated, grew up, and communicated with each other through sound, smell, and sight.

  Of all these puzzles, how dinosaurs came to rule the world is one of the most enduring. Douglass’s quarry preserves the heyday of giant dinosaurs—a time when a fantastic array of huge herbivores arched their elegant necks over fern-covered floodplains and tried to avoid an almost equally diverse complement of giant knife-toothed predators. For me, at least, this slice of Jurassic time is the acme of the dinosaur’s reign. This is a Jurassic classic. Marvelous as it is, though, the tableau contains a thread we can trace back to the mystery at its source. How did Apatosaurus and its varied kin get their start? How, exactly, did dinosaurs rise to rule the world in such flamboyant fashion? To find out, I have to look elsewhere, and the first stop is a few rock exposures over in the same park.

  A few miles down Dinosaur National Monument’s main drag is a little turnoff for the Sound of Silence Trail—a hike that always puts the Simon and Garfunkel song in a near-endless loop in my head as I walk past the low scrub and sandstone exposures beautifully carved by wind and water. Here, at a little kink in the trail, a deep swath of rust-red rock juts out of the ground in a long curve locally called “the Racetrack.” In this section of 220-million-year-old time, among preserved ripple marks and tunnels left behind by ancient worms, are the tracks of svelte, gracile dinosaurs—early members of a dynasty that had not yet come to power. The traces dinosaur
s left along muddy lakeshores are all that is here, and even those telltale footprints are rare signs of creatures that were only a marginal part of the prehistoric ecosystem. To understand dinosaur lives, we must examine these Triassic rocks—a time tens of millions of years before Apatosaurus and other dinosaurs stomped and bellowed their superiority. If we are truly going to appreciate dinosaurs for what they are, we have to go back to their humble beginnings.

  Two

  The Secret of Dinosaur Success

  The worst dinosaurs I have ever seen stand alongside Arizona’s stretch of I-40. The withered horrors bake in the sun outside Stewart’s Petrified Wood Shop, not far from the turnoff for Petrified Forest National Park. They are the cartoonish essence of dinosaurs I encountered as a child—all green skin and horrible teeth. One of the dreadful dinosaurs—what I can only assume was a shoddy attempt at a tyrannosaur—cradles in its jaws a frayed female mannequin with a red shock wig, and another weather-beaten model sits on a decaying sauropod, strapped in by a tangle of icicle lights. It’s Barbie meets The Beast from 20,000 Fathoms.

  Stewart’s isn’t the only highway stop to use dinosaurs as bait. A few more pit-stop misfits stand alongside the highway on the route to the nearby national park. If you want to get a driver’s attention, put out a dinosaur. Grotesque as they are, the sculptures make me wonder what really defines this famous group of animals. The misshapen roadside statues are clearly supposed to be dinosaurs, but many of them don’t look at all like the actual creatures paleontologists reconstruct. I try to think of some feature that unites all the sculptures, a common dinosaur denominator that connects all the terrible highway-side forms. I can’t pick anything out. They all have a cast of dinosaurishness about them, but why? The question sticks in my mind, but I don’t pull off the highway to give the dinosaur wannabes further consideration.