Dinosaurs, with their awe-inspiring size, terrifying claws and teeth, and otherworldly abilities, occupy a sacred place in our childhoods. They loom over museum halls, thunder through movies, and are a fundamental part of our collective imagination. In My Beloved Brontosaurus, the dinosaur fanatic Brian Switek enriches the childlike sense of wonder these amazing creatures instill in us. Investigating the latest discoveries in paleontology, he breathes new life into old bones.
Switek reunites us with these mysterious creatures as he visits desolate excavation sites and hallowed museum vaults, exploring everything from the sex life of Apatosaurus and T. rex’s feather-laden body to just why dinosaurs vanished. (And of course, on his journey, he celebrates the book’s titular hero, “Brontosaurus”—who suffered a second extinction when we learned he never existed at all—as a symbol of scientific progress.)
By now, we know that Apatosaurus is the dinosaur’s proper name. If you note the wrong term in front of a young fossil fan, you’ll get a swift correction. But you can’t keep a brontosaur down. Everyone knows the dinosaur’s name and we want “Brontosaurus” to exist. Even though some of my paleontologist friends have tried to match the name’s popularity by spreading the name of a previously unknown sauropod, Brontomerus—or “thunder thighs”—there isn’t going to be another dinosaur that can fill the cultural gap “Brontosaurus” left behind, which is funny, since it’s not like there’s some “Brontosaurus”- shaped hole in prehistory. Just look at Google’s Ngram Viewer—a service that tracks word use in books through time. We started using “Apatosaurus” and “Brontosaurus” at about the same time, but the Ngram reveals that “Brontosaurus” has always been the victor. Even from the 1970s on, when we knew that the dinosaur wasn’t real, the name still beats Apatosaurus in frequency. Whenever we mention Apatosaurus, we feel compelled to remind everyone that the dinosaur used to be called “Brontosaurus,” and so the discarded name persists. (I’m certainly compounding the problem here.) We can’t conjure Apatosaurus without the memory of “Brontosaurus” trailing close behind.
The torturous episode reminds me of when Pluto was demoted from planet status to the dwarf planet level. The cosmic body is still out there—scientists didn’t destroy it with a Death Star or other interplanetary weapon—but the outcry over the change was intense. Even many die-hard science fans loathed the technical decision. Why should a mundane label change matter so much? As the astronomer Mike Brown, whose work contributed to Pluto’s fall from interstellar grace, put it:
In the days that followed [Pluto’s demotion], I would hear from many people who were sad about Pluto. And I understood. Pluto was part of their mental landscape, the one they had constructed to organize their thinking about the solar system and their own place within it. Pluto seemed like the edge of existence. Ripping Pluto out of that landscape caused what felt like an inconceivably empty hole.
The Jurassic herbivore was a touchstone that put the rest of the archosaurian horde in context and helped us revive lost worlds in our imaginations. And the sauropod’s apparition remains a cultural baseline against the ever-shifting image of what dinosaurs are. To my mind, we didn’t lose a dinosaur so much as gain a much clearer view of a real Jurassic giant. The contrast between old “Brontosaurus” and dinosaurs as we know them now shows us just how much we have learned about dinosaur biology.
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, sailbacked 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.
Excerpted from MY BELOVED BRONTOSAURUS: ON THE ROAD WITH OLD BONES, NEW SCIENCE, AND OUR FAVORITE DINOSAURS by Brian Switek, published in April 2013 by Scientific American / Farrar, Straus and Giroux. Copyright © 2013 by Brian Switek. All rights reserved.