The Rise and Fall of the Dinosaurs Read online

  And what about the fifth special adaptation, being able to expel excess body heat? The lungs and air sacs helped with this too. There were so many air sacs, and they extended throughout so much of the body, snaking their way into bones and between internal organs, that they provided a large surface area for dissipating heat. Each hot breath would be cooled by this central air conditioning system.

  Putting it all together, that’s how you can build a supergiant dinosaur. If sauropods had lacked any one of these features—the long neck, the fast growth rates, the efficient lung, the system of skeleton-lightening and body-cooling air sacs—then they probably would not have been capable of becoming such behemoths. It wouldn’t have been biologically possible. But evolution assembled all of the pieces, put them together in the right order, and when the kit was finally assembled in the post-volcanic world of the Jurassic, sauropods suddenly found themselves able to do something no other animals, before or since, have been able to do. They became biblically huge and swept around the world; they became dominant in the most magnificent way—and they would remain so for another hundred million years.

  4

  Dinosaurs and Drifting Continents

  Stegosaurus

  Chapter Title art by Todd Marshall

  NESTLED WITHIN THE LEAFY STREETS of New Haven, Connecticut, on the northern fringes of the Yale University campus, there is a shrine. The Great Hall of Dinosaurs at Yale’s Peabody Museum may not bill itself as a place of spiritual pilgrimage, but that’s sure what it feels like to me. I get a shiver, as when I walked into Catholic mass as a child. It’s not a normal shrine—no statues of deities, flickering candles, or the hint of incense. It’s also not particularly magnificent, at least from the outside, tucked away inside a fairly nondescript brick building that blends in with the rest of the university’s lecture halls. But it houses relics that, to me, are as sacred as those you’ll find in most any religious shrine: dinosaurs. To me, there is nowhere better, anywhere on the planet, to go and immerse yourself in the wonder of the prehistoric world.

  The Great Hall was originally built in the 1920s to house Yale’s incomparable dinosaur collection, assembled over many decades by roughnecks who fanned across the American West and, for the right fee, sent fossil treasures eastward to be studied by the Ivy League elite. Coming up on its centennial, the gallery retains all of its original charm. This isn’t some New Age exhibit space with flashing computer screens and dinosaur holograms and a roaring soundtrack in the background. It’s a temple of science, where skeletons of some of the most iconic dinosaurs stand in solemn vigil, lights down low, in the sort of silence you really do expect in a church.

  Covering the entire east wall is a mural that stretches more than a hundred feet long and sixteen feet high. Taking four and a half years to complete, it was painted by a man named Rudolph Zallinger, who was born in Siberia, moved to the United States, and took up illustration professionally during the Great Depression. If he were around today, Zallinger would probably be working for an animation studio as a storyboard artist. He was a master at setting scenes and incorporating diverse sets of characters, telling grandiose stories with the stroke of his brush. His most famous work is undoubtedly The March of Progress—that often satirized timeline of human evolution in which a knuckle-walking ape gradually morphs into a spear-carrying man. More people have probably come to understand, or misunderstand, the theory of evolution through that one image than through all of the textbooks, school lectures, and museum exhibits the world over.

  But before he was painting humans, Zallinger was obsessed with dinosaurs. His mural inside the Great Hall—called The Age of Reptiles—is the crowning achievement of that stage of his career. It’s been on US postage stamps, was featured in a Life magazine series, and is either reproduced or plagiarized on all sorts of dinosaur paraphernalia. It’s the Mona Lisa of paleontology, surely the single most talked-about piece of dinosaur artwork that has ever been created. But really, it’s more akin to the Bayeux Tapestry, because it tells an epic tale of conquest. It’s the saga of how fishy creatures first emerged onto land, colonized a new environment, and diversified into reptiles and amphibians; then, of how these reptiles split off into the mammal and lizard lines, the proto-mammals having their day and the lizards following, eventually producing the dinosaurs.

  As the mural nears its end, some sixty feet and 240 million years from where it started, after a long journey through alien landscapes of primeval scaly beasts, the painting finally becomes engulfed in dinosaurs. It kind of sneaks up on you, as the transition from the lizards and proto-mammals to the dinosaurs unfolds incrementally across the canvas. Now it’s dinosaurs everywhere, of all shapes and sizes, some enormous and others blending into the background. Suddenly, the mural has taken on the feel of something quite different—of a Soviet propaganda poster with Stalin gesticulating before a crowd of peasants, or one of those hilariously self-aggrandizing frescoes in Saddam’s palaces. One glance at the dinosaurs and I feel the power. Strength, control, dominance. The dinosaurs were in command, and this was their world.

  The theropod Deinonychus stands guard over the Zallinger mural at the Peabody Museum, Yale University.

  Photo courtesy of the author

  This part of Zallinger’s mural beautifully encapsulates what it was like when dinosaurs had ascended to the peak of their evolutionary success. A monstrous Brontosaurus lounges in a swamp in the foreground, munching away on the ferns and evergreen trees surrounding the water. Off to the side, a bus-size Allosaurus rips into a bloodied carcass with its teeth and claws, its massive feet stomping on its prey for a little extra insult. Keeping a safe distance is a peaceful grazing Stegosaurus, which displays its full arsenal of bony plates and spikes just in case the carnivore has other ideas. Far in the background, where the swamp disappears into a wall of snowcapped mountains, another sauropod uses its long neck to vacuum shrubs off of the ground. Meanwhile, two pterosaurs—those flying reptiles closely related to dinosaurs, often called pterodactyls—chase each other overhead, dipping and diving through the tranquil blue sky.

  Odds are, this is the type of image that many of us think of when we think of dinosaurs. These are dinosaurs at their pinnacle.

  ZALLINGER’S MURAL IS not fiction. Like any good art, it takes a few liberties here and there, but it is largely rooted in fact. It’s based on those very same dinosaurs that stand in front of it in the Great Hall: familiar names like Brontosaurus, Stegosaurus, and Allosaurus. These dinosaurs lived during the Late Jurassic Period, about 150 million years ago. By this time, dinosaurs had already become the dominant force on land. Their victory over the pseudosuchians was 50 million years in the rearview mirror, and it had been a good 20 million years since some of the first giant long-necked species were splashing through the lagoons of Scotland. Nothing was holding back the dinosaurs anymore.

  We know a lot about the dinosaurs of the Late Jurassic. That’s because there are abundant fossils from this time, in many parts of the world. It’s just one of those quirks of geology: some time periods are better represented in the fossil record than others. It’s usually because more rocks were being formed during that time, or rocks of that age have better survived the rigors of erosion, flooding, volcanic eruptions, and all of the other forces that conspire to make fossils difficult to find. When it comes to the Late Jurassic, we enjoy two lucky breaks. First, there were hugely diverse communities of dinosaurs living alongside rivers, lakes, and seas all around the world—the perfect places to bury fossils in sediments that later turned to rock. Second, these rocks are today exposed in places convenient for paleontologists—in sparsely populated and dry regions of the United States, China, Portugal, and Tanzania, where annoyances like buildings, highways, forests, lakes, rivers, and oceans don’t cover up the fossil booty.

  The most famous Late Jurassic dinosaurs—those in Zallinger’s mural—come from a thick rock deposit that pokes out all across the western United States. Its technical term is the Morrison For
mation, named for a small town in Colorado where there are some beautiful exposures of its colorful mudstones and beige-tinged sandstones. The Morrison Formation is a monster: it can be found in thirteen states today, covering nearly four hundred thousand square miles (a million square kilometers) of the American scrublands. It is easily sculpted into low hills and undulating badlands, the sort of classic backdrop you see in Western films. It’s also the source rock for some of the country’s most important uranium ore deposits. And, yes, it’s a hotbed of dinosaurs, ones whose uranium-infused bones make Geiger counters sing.

  Paul Sereno in Wyoming.

  Photo courtesy of the author

  Excavating sauropod bones in the Morrison Formation near Shell, Wyoming. At the center back is Sara Burch, who later became an expert on T. rex arms (see Chapter 6).

  I worked in the Morrison Formation for two summers as an undergraduate. It’s where I cut my teeth excavating dinosaur skeletons. I was apprenticing in the lab of the University of Chicago’s Paul Sereno, whom we last met leading the expeditions to Argentina that turned up some of the world’s very oldest dinosaurs, the Triassic-age Herrerasaurus, Eoraptor, and Eodromaeus. But Paul seemed to study everything and do fieldwork everywhere: he had also found bizarre fish-eating and long-necked dinosaurs in Africa, he’d explored China and Australia, and he’d even described important fossils of crocodiles, mammals, and birds.

  In addition, like any academic paleontologist, Paul also had to spend time in the classroom. Each year he taught a popular undergraduate class called Dinosaur Science, which combined theory with practice. Because you can’t find dinosaurs anywhere near Chicago, the class would take a ten-day field trip each summer to Wyoming, where the students had the once-in-a-lifetime opportunity to dig dinosaurs with a celebrity scientist. Although at the time I had little prior experience, I was brought on as a teaching assistant, Paul’s right-hand man as we herded the students—a diverse lot, from premeds to philosophy majors—across the high desert.

  Paul’s field sites were located near the tiny town of Shell, secluded between the Bighorn Mountains to the east, and Yellowstone National Park a hundred miles to the west. Only eighty-three people were counted during the last census. When we were there in 2005 and 2006, the road signs boasted of merely fifty residents. But that’s a good thing for paleontologists. The fewer people in the way of the fossils, the better. And although Shell is a forgettable dot on the map, it can rightly stake its claim as one of the world’s dinosaur capitals. It is built on the Morrison Formation, surrounded by beautiful hills carved out of muted green, red, and gray rocks bursting with dinosaurs. So many dinosaurs have been found here that it’s hard to keep track, but the count is probably well over a hundred skeletons by now.

  As we drove west from Sheridan, on a surprisingly treacherous road across the rugged Bighorns, I felt I was on the trail of giants. Some of the biggest dinosaurs of all have been found in the Shell area: long-necked sauropods like Brontosaurus and Brachiosaurus, and the huge carnivores, like Allosaurus, that ate them. But I also felt I was walking in the footsteps of another type of giant: the explorers who found the first bones in this area in the late nineteenth century, the railwaymen and laborers who started a dinosaur rush and seized the moment to reinvent themselves as mercenary fossil collectors on the payrolls of gilded institutions like Yale University. They were a ragtag bunch, Wild West ruffians with cowboy hats, mustaches, and unkempt hair, who hacked giant bones out of the ground for months on end, and spent their free time raiding one another’s sites, constantly feuding and sabotaging and drinking and shooting. But these unlikely characters revealed a prehistoric world that nobody knew existed.

  The first Morrison fossils were surely noticed by the many Native American tribes scattered across the West, but the first recorded bones were collected by a surveying expedition in 1859. In March 1877 the real fun started. A railroad worker named William Reed was returning home from a successful hunt, rifle and pronghorn antelope carcass in tow, when he noticed some huge bones protruding out of a long ridge called Como Bluff, not too far from the railroad tracks in an anonymous expanse of southeastern Wyoming. He didn’t know it, but at the same time a college student, Oramel Lucas, was finding similar bones a few hundred miles to the south, in Garden Park, Colorado. That same month, a schoolteacher named Arthur Lakes had just found a cache of fossils near Denver. By the end of that March, the fever of discovery was spreading throughout the American West, to even the most remote villages and railway outposts.

  Like any prospecting rush, the dinosaur frenzy attracted a horde of questionable characters to the Wyoming and Colorado backcountry. Many of these men were grizzled opportunists on one mission: to convert dinosaur bones into cash. It didn’t take long for them to realize who was paying top dollar: two dapper East Coast academics, Edward Drinker Cope of Philadelphia and Othniel Charles Marsh of Yale University, the same men we briefly met two chapters ago, who studied some of the first Triassic dinosaurs found in western North America. Once chummy, these two scientists had let ego and pride metastasize into a full-on feud, which was so radioactive that they would do anything to one-up each other in an insane battle to see who could name the most new dinosaurs. Cope and Marsh were opportunists, too, and with each letter from a ranch hand or railway porter reporting more new dinosaur bones from the Morrison badlands, they saw the opportunity they had been craving but had been unable to yet fulfill: a chance to beat the other guy once and for all. And they both went for it.

  Cope and Marsh treated the West like a battlefield, employing rival teams that often acted more like armies, scooping up fossils wherever they went and sabotaging the other side whenever they could. Loyalties were fluid. Lucas worked for Cope, and Lakes teamed up with Marsh. Reed worked for Marsh, but members of his team defected to Cope. Pillaging, poaching, and bribing were the rules of the game. The madness continued for over a decade, and when it was over, it was hard to separate the winners from the losers. On the plus side, the so-called Bone Wars led to the discovery of some of the most celebrated dinosaurs, the ones that roll off the tongue of every schoolchild: Allosaurus, Apatosaurus, Brontosaurus, Ceratosaurus, Diplodocus, Stegosaurus, just to name a few. On the other hand, the mentality of constant warfare caused a lot of sloppiness: fossils haphazardly excavated and hastily studied, scraps of bone mistakenly christened as new species, different bits of the skeleton of the same dinosaur regarded as belonging to totally different animals.

  Edward Drinker Cope, the Bone Wars protagonist.

  AMNH Library.

  A page from Cope’s 1874 field notebook, depicting the fossil-rich rocks of New Mexico.

  AMNH Library.

  Cope’s sketch of a horned dinosaur (ceratopsian), from 1889, an insight into how he envisioned dinosaurs as living animals. (He was much better as a scientist than as an artist.)

  AMNH Library.

  Cope’s Bone Wars rival, Othniel Charles Marsh (center in the back row), and his team of student volunteers on their 1872 expedition to the American West.

  Courtesy of the Peabody Museum of Natural History, Yale University.

  Stegosaurus, one of the most famous dinosaurs discovered in the Morrison Formation during the Bone Wars period. Skeleton on display at the Natural History Museum in London.

  PLoS ONE.

  Wars can’t last forever, and as the nineteenth century turned over to the twentieth, sanity began to set in. New dinosaurs were still being found throughout the western United States, and most of the country’s leading natural history museums and many top universities had crews working somewhere in the Morrison Formation, but the chaos of the dinosaur rush was over. With less turbulence came several major discoveries: A graveyard of over 120 dinosaurs near the Colorado-Utah border, which later became Dinosaur National Monument. A pit with over ten thousand bones, mostly belonging to the superpredator Allosaurus, south of Price, Utah, called the Cleveland-Lloyd Dinosaur Quarry. A bone bed in the Oklahoma Panhandle discovered by a road crew and e
xcavated by a team of laborers who lost their jobs during the Great Depression and were put back to work digging up dinosaurs with money from Roosevelt’s New Deal. And the site near Shell that Paul Sereno was now working, with the assistance of me and a phalanx of undergraduate laborers paying hefty tuition for the privilege.

  Paul has discovered his fair share of dinosaur sites around the world, but the quarry near Shell is not one of them. Instead, it was a local rock collector who reported the first bones in the area. In 1932 she mentioned them to Barnum Brown, a New York paleontologist passing through town. We’ll meet Brown again in the next chapter, because much earlier in his career he discovered Tyrannosaurus rex. Brown was intrigued by the rock collector’s story and followed her to the lonely ranch of an octogenarian named Barker Howe, surrounded by sage-scented hills stalked by mountain lions and abuzz with grazing pronghorns. Brown liked what he saw and stayed the week. What he found was promising enough to convince Sinclair Oil to fund a full-scale expedition in the summer of 1934, to dig up what is now called the Howe Quarry.

  It turned out to be one of the most fantastic dinosaur excavations of all time. Once Brown’s crew starting digging, they kept finding skeletons everywhere, piled on top of each other and extending in all directions. More than twenty skeletons and four thousand bones in all, covering some 3,000 square feet (280 square meters), approaching the size of a basketball court. There was so much raw fossil material that it took about six months of daily work to excavate; the team broke camp only in mid-November, after enduring two months of heavy snow. The diggers found an entire ecosystem preserved in stone: there were giant long-necked plant-eaters like Diplodocus and Barosaurus, entangled with sharp-toothed Allosauruses and smaller herbivores that walked on two legs, called Camptosaurus. Something horrible had happened here some 155 million years ago. Judging from the contorted angles of their skeletons, the deaths of these animals were neither quick nor painless. Some of the sauropods were found upright, their heavy legs standing tall like columns, stuck in the ancient mud. It seems that these dinosaurs survived a flood, but then were mired in the muck when they tried to run away after the waters receded.