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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 excavated 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.


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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. Brown was delighted. He called the site an “an absolute, knockout dinosaur treasure trove!” and gleefully took his haul of dinosaurs back to New York, where they became crown jewels in the collection of the American Museum of Natural History. And then for many decades the Howe Quarry lay dormant, until a fossil collector from Switzerland named Kirby Siber rolled into Wyoming in the late 1980s. Siber is a commercial paleontologist: he digs up dinosaurs and sells them. It’s a thorny issue for many academic paleontologists like me, who see fossils as irreplaceable natural heritage that should be protected in museums, where they can be studied by researchers and enjoyed by the public, not sold off to the highest bidder. But there is a whole spectrum of commercial paleontologists, ranging from gun-toting criminals who illegally export fossils to diligent, conscientious, well-trained collectors whose knowledge and experience rival that of academics. Siber is in this latter category. In fact, he’s the archetype of this kind of collector. He is well respected by researchers and even founded his own dinosaur museum east of Zurich, called the Saurier Museum, which has some of the most remarkable dinosaur exhibits in Europe. Siber arranged access to the old Howe Quarry but didn’t find many dinosaurs. Brown’s team had pretty much cleared them all out. So the Swiss collector began prospecting in the surrounding gullies and hills, looking for new sites. It wasn’t long before he found a good one, about a thousand feet north of the original quarry. His backhoe first revealed some sauropod bones, and then a string of vertebrae from the backbone of a big, meat-eating theropod. Siber followed the spool-shaped bones, one by one, and before long it was clear that he had something special: the nearly complete skeleton of an Allosaurus, the top predator of the Morrison Formation ecosystem. It looked to be the single best fossil of this well-known dinosaur that had ever been found, more than 120 years after Marsh first named it during the heat of the Bone Wars. Allosaurus was the Butcher of the Jurassic, both figuratively and literally. This fierce predator stalked the Morrison floodplains and riverbanks—think T. rex but a little smaller and lighter, about two to two and a half tons in weight and thirty feet (nine meters) long as an adult, and better equipped for running.


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But it truly earned the title of Butcher, because paleontologists think it used its head like a hatchet to hack its prey to death. Computer models find that the thin teeth of Allosaurus couldn’t bite very strongly on their own, but the skull could withstand massive amounts of impact force. We also know that Allosaurus could open its jaws obscenely wide, so we think a hungry Allosaurus would attack with mouth agape and slash down at its prey, slicing through the skin and muscle with its thin but sharp teeth, which were lined up along its jaws like the blades of scissors. Many a Stegosaurus and Brontosaurus probably breathed its last this way. If for some reason the blood-lusting Allosaurus couldn’t quite knock off its victim using only its jaws of death, it could always finish the job with a couple of swipes of its clawed, three-fingered arms, which were longer and more versatile than the stubby little forelimbs of T. rex. Finding such a complete and well-preserved Allosaurus was one of the highlights of Siber’s career, but emotions were about to turn. After the summer’s excavation had ended, while Siber was at a fossil show peddling his wares and the Allosaurus skeleton remained in the ground, an agent from the US Bureau of Land Management (BLM) happened to be flying over that dusty stretch of northern Wyoming near the Howe Quarry. The agent was checking for signs of fire, part of his job monitoring public lands administered by the US government. But as he glided high above the badlands, he noticed that the dirt roads around the Howe Quarry had been shredded by tire marks. Somebody had been doing some heavy work that summer. That’s no problem around the Howe Quarry itself—it’s on private land, and Siber had the permission of the landowner. But the BLM agent wasn’t quite sure what was private ground and what was public, which could only be worked on by accredited scientists with BLM permission. So he doubled-checked and found that Siber had strayed a few hundred feet into BLM territory. Because Siber had no right to work there, he could no longer excavate the Allosaurus skeleton. It was probably an honest mistake, but a costly one. The BLM now had a problem. A gorgeous dinosaur skeleton was sitting in the ground, and the people who had found it and begun to excavate it couldn’t finish the job. So the agency assembled a crack team led by legendary paleontologist Jack Horner’s crew at Montana’s Museum of the Rockies (Horner is best known for two things: discovering the first dinosaur nesting sites in the 1970s and being the science advisor for the Jurassic Park films). Under the eye of television cameras and a throng of newspaper reporters, the academics took out the skeleton and trucked it up to Montana to be carefully conserved in the safety of the laboratory. The dinosaur turned out to be more spectacular than Siber could even have imagined.


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About 95 percent of the bones were there, an almost unheard of number for a large predatory dinosaur. At about twenty-five feet (eight meters) long, this Allosaurus was only about 60 to 70 percent grown. It was still a teenager, but it had already lived a tough life. Its body was covered with all types of maladies: broken, infected, and deformed bones that testify to the rough-and-tumble world of the Late Jurassic, when even the biggest predators didn’t have an easy time hunting behemoths like Diplodocus and Brontosaurus, when the sharpest teeth and claws were no guarantee of surviving a whack from the spiky tail of a Stegosaurus. The Allosaurus was nicknamed Big Al, and it became a celebrity dinosaur. It even had its own television special broadcast internationally by the BBC. But once the buzz died down, there remained a huge hole in the ground that was still full of all kinds of fossils that were buried underneath Big Al. Paul Sereno received permission from the BLM to use the site as a field laboratory to teach excavation techniques to his students, and that’s why we were taking three big SUVs full of undergraduates there. During that first season in Wyoming, in the summer of 2005, I spent many days parked out on the high desert, carefully removing globs of popcorn-textured mudstone to help the team uncover the skeleton of a Camarasaurus. It may not be one of the brand-name dinosaurs, but Camarasaurus is one of the more common species in the Morrison Formation. It is yet another type of sauropod, a close cousin of Brontosaurus, Brachiosaurus, and Diplodocus. Camarasaurus had the usual sauropod body: long neck that could reach several stories into the trees, small head with chisel-shaped teeth for stripping leaves, a massive frame that was about fifty feet (fifteen meters) long and weighed around twenty tons. It was probably the type of tasty plant-guzzler that Big Al and the other Allosauruses liked to eat, although its freakish size would have afforded it quite a lot of protection from even the scariest flesh-eaters. Maybe it was a Camarasaurus like this one that gave Big Al some of those nasty injuries. Camarasaurus is one of many enormous sauropods that have been found in the Morrison Formation. It’s joined by its famous cousins, the big three of Brontosaurus, Brachiosaurus, and Diplodocus. Then there are the under-the-radar players known only to the cognoscenti (or, perhaps, your average dinosaur-obsessed kindergartner): Apatosaurus, Barosaurus, and further on down the roster, Galeamopus, Kaatedocus, Dyslocosaurus, Haplocanthosaurus, and Suuwassea. There are various other sauropods that have been named based on scrappy bones, which may belong to even more species. Now, the Morrison Formation covers a wide swath of time, and was deposited across a huge geographic area. Not all of these sauropods lived together. But many of them did—they have been found at the same sites, their skeletons mingled together.


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The normal situation in the Morrison world was numerous varieties of sauropods cohabiting in the river valleys, their heavy footsteps thundering as they trawled the land in search of the daily hundreds of pounds of leaves and stems that sustained them. The skulls of Diplodocus (left) and Camarasaurus (right), two sauropods that used their differently shaped skulls and teeth to feed on different types of plants. Courtesy of Larry Witmer. What a weird scene to conjure up! It’s akin to imaging five or six different species of elephants crowded onto the African savannahs, all trying to find enough food to survive while lions and hyenas lurk in the background. The Morrison world was no less dangerous. If a sauropod was staggering around with an empty belly, then you could confidently bet an Allosaurus was hiding in the brush, ready to pounce at the long-neck’s moment of weakness. In addition to Allosaurus, there were many other predators below it on the food chain. There was Ceratosaurus, a twenty-foot-long mid-tier hunter with a frightening horn on its snout, a horse-size carnivore named Marshosaurus after the Bone Wars pugilist, and a donkey-size primitive cousin of T. rex called Stokesosaurus. Then you had the slashers: a number of lightly built, fast-running pests like Coelurus, Ornitholestes, and Tanycolagreus, the Morrison version of cheetahs. And all of these meat-gobblers, even Allosaurus, probably lived in fear of another monster that reigned near the top of the food chain. It’s called Torvosaurus, and we don’t know much about it, because its fossils are very rare. But the bones we have paint a terrifying picture: a knife-toothed apex predator that was thirty feet (ten meters) long and weighed about two and a half tons or perhaps more, not too far off from the proportions of some of the big tyrannosaurs that would evolve much later. It’s easy to understand why so many predators stalked the Morrison ecosystem: there were a lot of sauropods to eat. It’s much more difficult to explain how so many of these giant sauropods lived together. It’s an even greater puzzle because there were also plenty of other, smaller plant-eaters that feasted on shrubs closer to the ground: the plate-backed Stegosaurus and Hesperosaurus, the tanklike ankylosaurs Mymoorapelta and Gargoyleosaurus, the ornithischian Camptosaurus, and a whole zoo of small, fast-running fern-chewers like Drinker, Othnielia, Othnielosaurus, and Dryosaurus. The sauropods were also sharing space with all of these herbivores. So how did the sauropods do it? It turns out that their diversity was their key to success. There were many species of sauropods, yes, but they were all slightly different. Some were absolute colossuses: Brachiosaurus was around fifty-five tons, and Brontosaurus and Apatosaurus tipped the scales in the thirty-to-forty-ton range. But others were smaller: Diplodocus and Barosaurus were skinny little things, at least as far as sauropods go, weighing a mere ten to fifteen tons. So it goes without saying that some species would need more food than others.


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These sauropods also had different types of necks: that of Brachiosaurus arched proudly into the heavens with the erect profile of a giraffe, perfect for reaching the highest leaves, but Diplodocus may not have been able to lift its neck much past its shoulders and may have acted more like a vacuum cleaner sucking up shorter trees and shrubs. Finally, the heads and teeth of these sauropods differed as well. Brachiosaurus and Camarasaurus had deep, muscle-wrapped skulls and jaws lined with spatula-shaped teeth, so they could eat harder foods like thick stems and waxy leaves. But Diplodocus had a long head made up of delicate bones, with a row of tiny pencil-shaped teeth at the front of its snout. It would break its teeth if it tried to eat anything too hard. Instead, it spent its time stripping smaller leaves from the branches, its head rocking back and forth like a rake. Different species of sauropods were specialized for eating many different kinds of foods—and they had a lot to choose from, as the lush Jurassic forests were cluttered with towering conifers, with thickets of ferns, cycads, and other shrubs down below. The sauropods weren’t competing for the same plants, but dividing the resources among themselves. The scientific term for this is niche partitioning—when coexisting species avoid competing with each other by behaving or feeding in slightly different ways. The Morrison world was highly partitioned, which is a sign of just how successful these dinosaurs were. They were carving up almost every square inch of the ecosystem, a dizzying array of species flourishing alongside each other in the hot, humid, waterlogged forests and coastal plains of ancient North America. But what about Late Jurassic dinosaurs in other parts of the world? The story seems to be the same nearly everywhere we look. We also see a similar cast of diverse sauropods, smaller plant-eating stegosaurs, and small to large carnivores of the Ceratosaurus and Allosaurus mold in those other places with rich records of Late Jurassic fossils, like China, eastern Africa, and Portugal. It all comes down to geography. Pangea had started to break up many tens of millions of years before, but it takes a long time for a supercontinent to split. Landmasses can move apart from each other by only a few centimeters each year, about the same pace that our fingernails grow. Thus, there were still big land connections between most parts of the world persisting into the latest Jurassic. Europe and Asia were still globbed together, and they were linked to North America by a series of islands that could easily be traversed by a wayfaring dinosaur. These northern lands—called Laurasia—were beginning to split from southern Pangea, called Gondwana, which was a stuck-together mess of Australia, Antarctica, Africa, South America, India, and Madagascar. Laurasia and Gondwana were intermittently connected by land bridges when sea level was low, and even during times of higher water, other islands provided a convenient migratory route between north and south.


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The Late Jurassic, then, was a time of global uniformity. The same suite of dinosaurs ruled every corner of the globe. Majestic sauropods divided food among them, reaching a peak of diversity unmatched by any other large plant-eaters in Earth history. Smaller plant-chewers prospered in their shadows, and a motley crew of meat-eaters took advantage of all of that herbivore flesh. Some, like Allosaurus and Torvosaurus, were the first truly giant theropods. Others, like Ornitholestes, were the founding members of that dynasty that would eventually produce Velociraptor and birds. The planet was sweltering and the dinosaurs were able to move around wherever they wanted. This was the real Jurassic Park. 145 MILLION YEARS ago, the Jurassic Period transitioned into the final stage of dinosaur evolution, the Cretaceous Period. Sometimes the switch between geological periods happens with a flourish, as when the megavolcanoes closed out the Triassic. Other times, it’s barely noticeable, and more a matter of scientific bookkeeping, a way for geologists to break up long stretches of time without any major changes or catastrophes. The changeover between the Jurassic and Cretaceous is that type of boundary. There was no calamity like an asteroid impact or a big eruption that ended the Jurassic, no sudden die-off of plants and animals, no brave new world as the Cretaceous dawned. Rather, the clock just ticked over, and the diverse Jurassic ecosystems of giant sauropods, plate-backed dinosaurs, and small to monstrous meat-eaters continued into the Cretaceous. That’s not to say, however, that nothing changed, for plenty was happening to the Earth around the Jurassic-Cretaceous boundary—no apocalyptic disasters but slower changes to the continents, oceans, and climate occurring over some 25 million years. The hothouse world of the Late Jurassic was interrupted by a cold snap, followed by a turn to more arid conditions, before things swung back to normal in the Early Cretaceous. Sea levels started to fall during the latest Jurassic and stayed low across the boundary, until the waters started to rise again some 10 million years into the Cretaceous. With low sea levels came a lot more exposed land, which allowed dinosaurs and other animals to move around even more easily than during the Late Jurassic. Pangea continued to rupture, the fragments of the supercontinent moving farther and farther apart from one another as time marched on. Gondwana, that huge expanse of southern lands, finally began to split, the cracks starting to define the shapes of today’s southern hemisphere continents. First the conjoined mass of Africa and South America detached from the section of Gondwana containing Antarctica and Australia, and then this latter chunk also began to fracture. Volcanoes welled up through the fissures, and although none were on the scale of the monster eruptions at the end of the Permian or Triassic, they would have brought with them the same nasty stew of environment-poisoning lava and gases. None of these changes were particularly deadly on their own, but together they were an insidious cocktail of dangers.


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The long-term shifts in temperature and sea level were probably unrecognizable to dinosaurs, the sort of thing that neither they nor any of us, had we been around, would ever have noticed in one lifetime. Plus, in the dinosaur-eat-dinosaur world of the Late Jurassic and Early Cretaceous, the Brontosauruses and Allosauruses had more important things to stress over than little changes in the tide line or slightly cooler winters. Given enough time, however, these changes built up and became silent killers. By about 125 million years ago, some 20 million years after the Jurassic ended, a new Cretaceous world had emerged, ruled by a very different suite of dinosaurs. The most obvious change had to do with the most prominent dinosaurs—the gargantuan sauropods. Once so diverse in the Late Jurassic Morrison ecosystems, the long-necks suffered a crash in the Early Cretaceous. Almost all of the familiar species like Brontosaurus, Diplodocus, and Brachiosaurus went extinct, while a new subgroup called the titanosaurs began to proliferate, eventually evolving into supergiants like the middle Cretaceous Argentinosaurus, which at more than a hundred feet (thirty meters) long and fifty tons in mass was the largest animal known to have ever lived on land. But despite the outlandish sizes of the new Cretaceous species, never again would sauropods be as dominant as they were in the Late Jurassic; never again would they boast such a variety of necks and skulls and teeth that allowed them to exploit so many ecological niches. As sauropods suffered, smaller plant-eating ornithischians blossomed, becoming ubiquitous midsize herbivores in ecosystems around the world. Most famous of these is surely Iguanodon, one of the very first fossils to be called a dinosaur, after it was discovered in the 1820s in England. Iguanodon was about thirty feet (ten meters) long and weighed a few tons. It had a spike on its thumb for defense and a beak at the front of its mouth for snipping plants, and it could switch between walking on all fours and sprinting on its hind legs. Its line would eventually go on to produce the hadrosaurs, or duck-billed dinosaurs, the group of amazingly successful herbivores that thrived at the very end of the Cretaceous, alongside their nemesis, T. rex. That was still many tens of millions of years in the future, but those seeds were planted in the Early Cretaceous. While the iguanodons were stepping in for the smaller sauropods, there were also changes afoot among ground-feeding herbivores. The plate-backed stegosaurs went into long-term decline, gradually wasting away until the last surviving species succumbed to extinction sometime in the Early Cretaceous, snuffing out this iconic group once and for all. Replacing them were the ankylosaurs, freakish creatures whose skeletons were covered in armor plates, like a reptilian Panzer. They had originated back in the Jurassic and remained marginal understudies in most ecosystems, but they exploded in diversity as stegosaurs regressed.


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Ankylosaurs were some of the slowest, stupidest dinosaurs of all, but they made a living happily chomping ferns and other low-lying vegetation, their body armor making them impervious to attack. Not even the sharpest-toothed predator could get in a good chomp when it had to bite through several inches of solid bone. Then there were the meat-eaters. With so much going on with their herbivore prey, it’s no surprise that theropods experienced their own drama as the Jurassic turned into the Cretaceous. A much greater diversity of small carnivores appeared, and some of them started to experiment with weird diets, trading in meat for nuts, seeds, bugs, and shellfish. One group, the scythe-clawed therizinosaurs, even went full vegetarian. On the other end of the size spectrum, a weird clan of large theropods called spinosaurids evolved sails on their backs and long snouts full of cone-shaped teeth, and moved into the water, where they started behaving like crocodiles and eating fish. However, as is usually the case when it comes to theropods, the most gripping story line concerns the apex predators. Like their smaller brethren, the top-of-the-food-chain supercarnivores also experienced massive upheaval across the Jurassic-Cretaceous boundary. These species are some of my favorites, because the very first dinosaurs that I studied—as an undergraduate working with Paul Sereno, during those same summers we dug up Late Jurassic sauropods in Wyoming—were giant theropods from the Early Cretaceous of Africa. WHEN I WAS a teenager, I watched movies and listened to music and went to baseball games—the normal stuff—but my hero wasn’t some athlete or actor. He was a paleontologist. Paul Sereno, the National Geographic Explorer in Residence, dinosaur hunter extraordinaire, leader of expeditions all over the world, and one of People magazine’s 50 Most Beautiful People, in the issue with Tom Cruise on the cover. I was a dinosaur-obsessed high schooler, and I followed Sereno’s work like a rock star’s groupie. He taught at the University of Chicago, not too far from where I lived, and he grew up in Naperville, Illinois, a suburb where some of my cousins were from. He was a local kid who did good, who became a celebrity scientist and adventurer, and I wanted to be like him. I met my hero when I was fifteen years old, when he was lecturing at a local museum. I’m sure Paul was used to meeting fanboys, but I upped the weird factor when I shoved a manila envelope in his face, so full of photocopied magazine pages that it couldn’t be sealed shut. You see, I was also a budding journalist at the time, or at least I thought I was, and I was churning out articles for amateur paleontology mags and websites at a pace that bordered on the creepy. Many of them were about Paul and his discoveries, and I wanted him to see the things I had written about him. My voice cracked as I handed him the envelope. It was awkward.


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But Paul was very nice to me that afternoon, and after a long chat, he told me to keep in touch. I met him a few more times over the next couple of years. We exchanged a lot of e-mails, and when I decided to put journalism aside and dive into paleontology as a career, there was only one college that I wanted to attend: the University of Chicago, so I could learn under Paul. Chicago accepted my application, and I enrolled in the autumn of 2002. During freshman week, I met with Paul and begged him to let me work in his basement fossil lab, where his newest treasures from Africa and China were being revealed, entirely new dinosaurs coming into focus as sand grains were scrubbed away from the bones. I would do anything—even wash the floors or clean the shelves. Thankfully, Paul channeled my enthusiasm elsewhere. He began by teaching me how to conserve and catalog fossils, and then one day he had a surprise. “How would you like to describe a new species of dinosaur?” he asked while leading me to a row of cabinets. Spread in front of me, in drawer after drawer, were fossils of Early to middle Cretaceous dinosaurs that Paul and his team had recently brought back from the Sahara Desert. About a decade earlier, after concluding his wildly successful expeditions to Argentina that netted the primitive dinosaurs Herrerasaurus and Eoraptor, Paul shifted his attention to northern Africa. At the time, little was known about African dinosaurs. A few excursions led by Europeans during the colonial period had found some intriguing fossils in places like Tanzania, Egypt, and Niger, but once the colonizers left, so too did most interest in collecting dinosaurs. Not only that, but some of the most important African collections—made by the German aristocrat Ernst Stromer von Reichenbach, from the Early to mid Cretaceous rocks of Egypt—weren’t around anymore. They had the great misfortunate of being kept in a museum just a few blocks from Nazi headquarters in Munich and were destroyed by an Allied bombing raid in 1944. When Paul turned his focus to Africa, all he had to go by were some photographs, a few published reports, and a smattering of bones in those European museums that weren’t blitzed during the war. That didn’t stop him, though. He mounted a reconnaissance trip to Niger, in the heart of the Sahara, in 1990. His team found so many fossils that they returned again in 1993, 1997, and several times after that. These were arduous trips—proper Indiana Jones–style expeditions, often lasting for several months and afflicted by the occasional bandit attack or civil war. As something of a break, they took a year off and visited Morocco in 1995.


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There, too, they uncovered a bounty of bones, including the gorgeously preserved skull of a giant flesh-eater called Carcharodontosaurus, a dinosaur that Stromer had originally named based on a partial skull and skeleton from Egypt that were among those fossils incinerated in the Munich museum. All told, Paul’s African expeditions collected some one hundred tons of dinosaur bones, many of which still sit in a warehouse in Chicago, waiting to be studied. Those dinosaurs not in the warehouse are inventoried at Paul’s lab, and these were the bones laid out before me. Some belonged to a weird sauropod called Nigersaurus, a plant-inhaling machine with hundreds of teeth packed into the front edge of its jaws. There were several elongate vertebrae of the fish-eating spinosaurid Suchomimus—the bones that supported the tall sail that extended along its back. Nearby was the gnarly-textured skull of a carnivore called Rugops, which probably scavenged carcasses as much as it hunted. And these fossils weren’t only dinosaurs. There was the man-size cranium of the forty-foot-long crocodilian Sarcosuchus—appropriately nicknamed SuperCroc by the media-savvy Sereno—and the wing bones of a large pterosaur, and even some turtles and fish. All of these fossils came from rocks that formed over some ten to fifteen million years of the Early to middle Cretaceous, in river deltas and along the shores of warm tropical seas fringed by mangrove forests, back when the Sahara was a steamy swampy jungle instead of a desert. As my eyes darted among the fossils, the cast of characters expanding as each drawer opened, Paul stopped and picked up a bone. It was part of the face of a huge-meat eating dinosaur that looked to be almost as big as T. rex. There were other things in the same drawer: a piece of a lower jaw, some teeth, and a fused mass of bones from the back of the skull, which would have surrounded the brain and ears. Paul recounted how he’d discovered the specimens a few years back in a desolate part of Niger called Iguidi, just west of a desert oasis, in red sandstones left by a river between 100 and 95 million years ago. He could tell that they were similar to the Carcharodontosaurus bones that he’d collected in Morocco, but the match wasn’t perfect. He wanted me to figure out the discrepancy. I was nineteen years old, and this was my first taste of the detective work that goes into identifying dinosaurs. It was intoxicating. I spent the remainder of the summer scrutinizing the bones, measuring and photographing them, comparing them with other dinosaurs. I concluded that the bones from Niger were indeed very similar to the Moroccan skull of the species Carcharodontosaurus saharicus but found that there were also so many differences that the two could not have belonged to the same species. Paul agreed, and we wrote up a scientific paper describing the Niger fossils as a new dinosaur, a close but distinct relative of the Moroccan species.


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We called it Carcharodontosaurus iguidensis. It was the alpha predator of those humid seaside ecosystems of mid-Cretaceous Africa, a forty-foot-long, three-ton beast that lorded over all of the other dinosaurs that Paul had been trawling out of the Sahara. There was a whole group of dinosaurs like Carcharodontosaurus that lived throughout the world during the Early to middle Cretaceous. They are named, perhaps unoriginally, the carcharodontosaurs. Among the family album are three species—Giganotosaurus, Mapusaurus, and the hauntingly named Tyrannotitan—all from South America, which during the Early to middle Cretaceous was still connected to Africa. Other siblings lived farther afield: Acrocanthosaurus in North America, Shaochilong and Kelmayisaurus in Asia, and Concavenator in Europe. And there’s also another one from the Sahara, called Eocarcharia, which Paul and I described based on some skull bones he found on another expedition to Niger. It was about 10 million years older than Carcharodontosaurus, and only about half the size. It was about as brutish as a dinosaur could get, with a gnarled knob of bone and skin above each eye that gave it an evil scowl and may have even been used to head-butt prey into submission. These carcharodontosaurs fascinated me. They were basically doing what tyrannosaurs would do many tens of millions of years later: supersizing their bodies, developing an arsenal of predatory weapons, and terrorizing every living thing from their undisputed perch at the top of the food pyramid. Where did they come from? How did they spread around the world and become so dominant? And then what happened to them? There was only one way to answer these questions. I needed to build a family tree. Genealogy is a key to understanding history, which is why so many people, me included, are obsessed with our own family trees. Knowing the connections among kin helps to untangle how our families have changed over the centuries: when and where our ancestors lived, when a migration or an unexpected death occurred, how the family merged with others through marriages. The same with dinosaurs. If we can read their family tree—or their phylogeny, as paleontologists technically call it—we can use it to illuminate their evolution. But how do you make a family tree for dinosaurs? Carcharodontosaurus doesn’t have a birth certificate, and the ancestor of Giganotosaurus wasn’t granted a visa when it left Africa for South America. But there is another type of clue coded in the fossils themselves. Evolution causes change over time, particularly in the appearances of organisms. When two species diverge from each other, usually only minor differences separate them, and you may have a hard time telling them apart at a glance, but as time ticks on and the two lineages go their separate ways, they become more and more different from each other. It’s the same reason that I look a lot like my father but barely resemble my third cousins.


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The other thing evolution occasionally does is produce new things—an extra tooth, or a horn sticking out of the forehead, or a mutation that causes a finger to be lost. These novelties will be inherited by the descendants of the first critter to develop them, but they won’t be seen in cousins that had already split off and started evolving down their own path. I’ve inherited all kinds of things from my parents, and my children will then inherit those things from me. But if my cousin suddenly goes weird and grows a set of wings, they can’t be passed on to me, because there is no direct line of descent between us. That means, thankfully in this case, that none of my children get those wings either. Genealogy, therefore, is written into the way we look. On the whole, dinosaurs with similar skeletons are probably more closely related to each other than to other species that look drastically different. But if you want to know if two dinosaurs truly are close brethren, you need to look out for those evolutionary novelties, because animals that possess a newly evolved feature like an extra finger must be more closely related to each other than to ones that don’t have it. That’s because they must have inherited that novelty from a common ancestor, which developed the feature and started an evolutionary domino effect of passing it down the bloodline, generation by generation. Any species with that extra finger is part of the bloodline; anything without it is likely on another side branch of the family tree. So to build a genealogy of dinosaurs we need to pore over their bones, find a way to assess how similar and different they are, and identify evolutionary novelties and which subsets of the dinosaurs in question share them. When I became intrigued by carcharodontosaurs, I began to track down as much information on each species as I could. I visited museums to study skeletons firsthand, and I gathered photographs, drawings, published literature, and notes for some of the more exotic fossils in faraway places that were inaccessible to an unfunded undergraduate. The more I looked, I recognized features of the bones that varied among species. Some carcharodontosaurs had deep sinuses surrounding their brain, others did not. The giant ones like Carcharodontosaurus had massive, bladelike teeth that kind of resembled those of sharks (hence its name, which means “shark-toothed lizard”), but the smaller species had much daintier chompers. The list went on and on, until I had come up with ninety-nine different ways that some of these predators differed from others. Now it was time to make some sense out of this information. I turned my list into a spreadsheet: each row a species, each column one of the features of the anatomy, each data cell filled with a 0, 1, or 2 denoting the different versions of each feature seen in that species. Dainty teeth in Eocarcharia, 0; sharky teeth in Carcharodontosaurus, 1.


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Then I opened the spreadsheet in a computer program that uses algorithms to search through the maze of data and generate a family tree. It pinpoints which anatomical features are novelties and then identifies which species share them. This may sound trivial, but the computer is necessary because the distribution of novelties can be complicated. Some are seen in many species—those big sinuses around the brain are present in most carcharodontosaurs. Others are much rarer, like the shark-mimic teeth, which are seen only in Carcharodonosaurus, Giganotosaurus, and their closest kin. The computer is able to take all of this complexity and recognize a Russian doll pattern. If two species share many novelties between only themselves, they must be each other’s closest relatives. If those two species share other novelties with a third animal, those three must be more closely related to one another than to the remainder of the dinosaurs. And so on, until a complete family tree has been drawn. This whole process is what we in the business call a cladistic analysis. My family tree of carcharodontosaurs helped me unravel their evolution. First, it clarified where these colossal carnivores came from and how they rose to glory. They got their start in the Late Jurassic and are very close relatives of that most terrifying predator of the Jurassic, the Butcher itself, Allosaurus. In effect, they evolved from a legion of hypercarnivores that was already incumbent in the apex predator niche, and then they escalated things further by becoming larger, stronger, and fiercer when their ancestors went extinct at the end of the Jurassic, 145 million years ago, during that long night of environmental and climate change. Did they drive these other allosaurs to extinction or take advantage when they succumbed for other reasons? We don’t yet know the answer. In either event, the carcharodontosaurs found a way to usurp the place of their forebears and, as the Cretaceous dawned, the kingdom was now theirs. For the next 50 million years or so, deep into the middle Cretaceous, the carcharodontosaurs ruled the world. The genealogy also gives insight into something else: why these flesh-gouging monsters lived where they did. Because they originated when most of the continents were still connected during the Late Jurassic, the first carcharodontosaurs easily spread around the world. As time went on and the continents fragmented further, different species became isolated in different areas. The structure of their family tree shows this—it reflects the motion of the continents. Some of the last carcharodontosaurs to evolve were a clan of South American and African species. (South America and Africa remained connected to each other long after links with North America, Asia, and Europe were severed.) Isolated south of the equator, the members of this clan—Giganotosaurus, Mapusaurus, and the Carcharodontosaurus from Niger that I studied with Sereno—grew to sizes previously unheard of for meat-eating dinosaurs. Nevertheless, as ferocious as these carcharodontosaurs were, they wouldn’t stay on top forever.


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Living alongside them, in their shadows, was another breed of carnivore. Smaller, faster, brainier. Their name, the tyrannosaurs. They would soon make their move and begin a new dinosaur empire.


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The Rise and Fall of the Dinosaurs 5 The Tyrant Dinosaurs Qianzhousaurus Chapter Title art by Todd Marshall ONE SWELTERING SUMMER DAY IN 2010, a backhoe operator in the southeastern Chinese city of Ganzhou heard a loud crunch. He expected the worst. His crew was racing to finish an industrial park—a sprawling monotony of offices and warehouses of the sort that I’ve seen crop up all over China during the past decade. Any delay could be pricey. Maybe he had hit impenetrable bedrock, an old water main, or another nuisance that would stall the project. When the dirt and smoke cleared, however, he didn’t see any mangled pipes or wires. There was no bedrock in sight. Instead, something very different came into focus: fossilized bones, lots of them, some of them enormous. Construction halted. The workman didn’t have any advanced degrees or training in paleontology, but he realized his discovery was important. He knew it must be a dinosaur. His homeland had become the epicenter of new dinosaur discoveries, the place where about half of all new species are being found these days. So he called over his foreman, and that is when the madness began. This dinosaur had been buried for more than 66 million years, but now its fate was down to the kind of quick decisions that unfold during a crisis. Word started to leak out. In a panic, the foreman called a friend from town, a fossil collector and dinosaur enthusiast known to posterity only as Mr. Xie. Grasping the gravity of the discovery, Mr. Xie—his honorific and hazy surname recalling one of those shadowy characters in a Bond film—raced to the worksite and rang up some mates at the town’s mineral resources department, a branch of the local government. The game of telephone continued and the agency was able to round up a small team to gather the bones. It took them six hours, but they collected every scrap they could find. They filled twenty-five bags with dinosaur bits and took them to the town’s museum for safekeeping. Their timing was perfect—ominously so. Just as the team was finishing, three or four fossil traffickers appeared on the scene. Like bloodhounds, these black-market hucksters caught the scent of a new dinosaur and wanted to buy it for themselves. A little bit of bribe money would turn into a major payday if they sold the new dinosaur to some wealthy foreign businessman with a taste for exotic fossils. This kind of thing is all too common in China and in many other parts of the world (although it is often against the law). It is heartbreaking to think of the fossils that have been lost to the dark underworld of illegal dealing and organized crime. But this time, the good guys won. When scientists examined the fossils in the safety of the local museum and began to piece together the bones, they quickly recognized how incredible this new discovery was.


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It wasn’t just a jumble of random bones but a nearly complete skeleton of a predatory dinosaur, one of the massive, sharp-toothed behemoths that always seem to play the villain in films and television documentaries. And the skeleton looked similar to a famous dinosaur from halfway around the world: the great Tyrannosaurus rex, which stalked the forests of North America at about the same time that these red rocks from Ganzhou, which the backhoe operator was plowing through to lay his foundation, were formed. Then it clicked: they were looking at an Asian tyrannosaur. The ferocious ruler of a 66-million-year-old world of dense jungles, sticky with humidity all year round, with swamps and the occasional quicksand pit peppered in between the ferns, pines, and conifers. It was an ecosystem teeming with lizards, feathered omnivorous dinosaurs, sauropods, and swarms of duck-billed dinosaurs, some of which got caught in the slushy death pits and were preserved as fossils. The ones lucky enough to survive were tasty prey for the creature the workman stumbled upon by pure chance: one of the closest relatives of T. rex. THAT BLESSED WORKMAN. He had made a discovery of the sort most paleontologists dream of. Lucky for me, this was a finding that I got to be part of without having to do the hard work of hunting it myself. A few years after the craziness of that late summer day in Ganzhou, I was at a conference at the Burpee Museum of Natural History, in the frozen winter wasteland of northern Illinois, just up the road from where I grew up. Scientists from around the world had gathered to discuss the extinction of the dinosaurs. Earlier in the day, I was mesmerized by a presentation from Junchang Lü, my eyes opening wider with each slide, as photo after photo of beautiful new fossils from China flashed across the screen. I knew Professor Lü by reputation. He was widely regarded as one of China’s top dinosaur hunters, a man whose discoveries helped establish his country as the world’s most exciting place for dinosaur research. Professor Lü was a star. I was a young researcher, but to my great surprise Professor Lü approached me. I shook his hand and congratulated him on his talk, and we exchanged a few other pleasantries. But there was urgency in his voice, and I noticed he was clutching a folder thick with photos. Something was going on. Professor Lü told me he had been tasked with studying a spectacular new dinosaur found by a construction worker in southern China a few years before. He knew it was a tyrannosaur, but it seemed peculiar. It was different enough from T. rex that it must be a new species. And it looked kind of similar to a weird tyrannosaur that I had described a few years earlier as a graduate student—a slender, long-snouted predator from Mongolia called Alioramus. But Professor Lü wasn’t sure. He wanted a second opinion.


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Of course I offered to help in any way I could. Professor Lü, or Junchang, as I soon knew him, told me all about his past—how he grew up poor in Shandong Province, on China’s eastern coast, a child of the Cultural Revolution who staved off hunger by picking wild vegetables. Then, once the winds of politics changed, he studied geology in college, went to Texas to do his PhD, and came back to Beijing to take up one of the most vaunted jobs in Chinese paleontology, a professorship at the Chinese Academy of Geological Sciences. Junchang—the peasant turned professor—became my friend. Not too long after we met at the conference, he invited me to China to help him study the new tyrannosaur and write up a scientific paper describing the skeleton. We scrutinized each part of the skeleton, comparing it to all other tyrannosaurs. We confirmed that it was a close cousin of T. rex. A little over a year later, in 2014, we unveiled the workman’s chance discovery as the newest member of the tyrannosaur family tree, a new species that we called Qianzhousaurus sinensis. The formal name is a something of a tongue twister, so we nicknamed it Pinocchio rex, in reference to its funny long snout. The press got wind of the discovery—journalists seemed to love the silly nickname—and Junchang and I were amused to see our faces splashed across the British tabloids the morning after our announcement. The facial bones of Alioramus altai, a new species of long-snouted tyrannosaur from Mongolia that I described as a PhD student. Photograph by Mick Ellison. Qianzhousaurus is part of a surge of new tyrannosaur discoveries over the past decade that is transforming our understanding of this most iconic group of meat-eating dinosaurs. T. rex itself has been in the limelight for over a century, since it was first discovered in the early 1900s. It’s the king of dinosaurs, a forty-foot-long, seven-ton behemoth on a first-name basis with almost everyone on the planet. Later during the twentieth century, scientists discovered a few close relatives of T. rex that were also impressively large and realized that these big predators formed their own branch of dinosaur genealogy, a group that we called the tyrannosaurs (or Tyrannosauroidea in formal scientific parlance). However, paleontologists struggled to understand when these fantastic dinosaurs originated, what they evolved from, and how they were able to grow so large and reach the top of the food chain. These questions have remained unanswered until now. Over the last fifteen years, researchers have recovered nearly twenty new tyrannosaur species at locations the world over. The dusty southern Chinese construction site that yielded Qianzhousaurus is one of the least unusual places where a new tyrannosaur has been found. Other new species have been pried from the sea-battered cliffs of southern England, the frigid snowfields of the Arctic Circle, and the sandy expanses of the Gobi Desert.


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These finds have allowed my colleagues and me to build a family tree of tyrannosaurs in order to study their evolution. The results are surprising. It turns out that tyrannosaurs were an ancient group that originated more than 100 million years before T. rex, during those golden days of the Middle Jurassic when dinosaurs were beginning to prosper and long-necked sauropods, like the creatures whose footprints we found in that ancient Scottish lagoon, were rumbling across the land. These first tyrannosaurs weren’t very impressive. They were marginal, human-size carnivores. They continued this way for another 80 million years or so, living in the shadows of larger predators, first Allosaurus and its kin in the Jurassic, and then the fierce carcharodontosaurs in the Early to middle part of the Cretaceous. Only then, after that interminable period of evolution in anonymity, did tyrannosaurs start growing bigger, stronger, and meaner. They reached the top of the food chain and ruled the world during the final 20 million years of the Age of Dinosaurs. THE STORY OF tyrannosaurs begins with the discovery of T. rex, the namesake of the group, in the early days of the twentieth century. The scientist who studied T. rex was a good friend of President Theodore Roosevelt’s, a boyhood chum who shared Teddy’s love for nature and exploration. His name was Henry Fairfield Osborn, and during the early 1900s, he was one of the most visible scientists in the United States. Osborn was president of New York’s American Museum of Natural History and of the American Academy of Arts and Sciences, and in 1928 he even graced the cover of Time magazine. But Osborn was no normal man of science. His blood ran blue: his father was a railroad tycoon, his uncle the corporate raider J. P. Morgan. He seemed to be a member of every wood-paneled, smoke-filled, good-old-boy backroom club there was. When he wasn’t measuring fossil bones, he was rubbing shoulders with New York’s social elite in the penthouses of the Upper East Side. Osborn is not remembered very fondly today. He wasn’t a very nice man. He used his wealth and political connections to push pet ideas on eugenics and racial superiority. Immigrants, minorities, and the poor were seen as enemies. Once Osborn even organized a scientific expedition to Asia with the hope of finding the very oldest human fossils, to prove that his species couldn’t possibly have originated in Africa. He couldn’t fathom being the evolutionary descendent of an “inferior” race. No wonder he is often dismissed today as just another bygone bigot. Osborn is probably not the type of guy I would want to have a beer—or more likely, a really fancy cocktail—with if I found myself in Gilded Age New York. (I speculate, but he might not have sat down with me anyway, leery of my very ethnic-sounding Italian name.) Nevertheless, there’s no denying that Osborn was a clever paleontologist and an even better scientific administrator.


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It was in his capacity as president of the American Museum of Natural History—the august institution that rises like a cathedral on the west side of Central Park, where I would later work on my PhD—that Osborn made one of the best calls in his career. He decided to send a sharp-eyed fossil collector named Barnum Brown out to the American West in search of dinosaurs. We briefly met Brown in the last chapter, when a much older version of him was excavating Jurassic dinosaurs in the Howe Quarry in Wyoming. He was an unlikely hero. He grew up in a speck of a village on the Kansas prairie, a coal-company town where only a few hundred people lived. Maybe his parents gave him a flamboyant name inspired by the circus showman P. T. Barnum in some attempt to escape the drudgery of their rural life. The young Barnum didn’t have many people around to talk to, but he was surrounded by nature, and he became infatuated with rocks and shells. He even started a little museum at his house, something my dinosaur-obsessed younger brother, also growing up in a placid Midwestern town, would later do after seeing Jurassic Park in the cinema. Brown went on to study geology in college and then made his way from the small time to New York City in his twenties. It was there he met Osborn and was hired as a field assistant, tasked with bringing huge dinosaurs from the unexamined expanses of Montana and the Dakotas to the bright lights of Manhattan, where socialites who had never slept a night outdoors could gawk at the stupendousness of it all. Barnum Brown (left) and Henry Fairfield Osborn digging up dinosaur bones in Wyoming, 1897. AMNH Library. This is how Brown found himself, in 1902, in the desolate badlands of eastern Montana. While out prospecting the hills, Brown came across a jumble of bones. Part of a skull and jaw, some vertebrae and ribs, bits of the shoulder and arm, and most of the pelvis. The bones were enormous. The size of the pelvis indicated an animal that stood several meters tall, certainly much larger than a human. And they were clearly the remains of a muscular creature that could run relatively fast on two legs—the characteristic body type of a meat-eating dinosaur. Other predatory dinosaurs had been found before—like Allosaurus, the Butcher of the Late Jurassic—but none of these were anywhere near the colossal size of Brown’s new beast. He was on the cusp of turning thirty years old, and he had made a discovery that would define him for the rest of his life. Brown sent his discovery back to New York, where Osborn was anxiously awaiting the shipment. The bones were so big, they took years to clean up and assemble into a partial skeleton that could be exhibited to the public. This work was mostly done by the end of 1905, when Osborn announced the new dinosaur to the world.


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He published a formal scientific paper designating the new dinosaur as Tyrannosaurus rex—a beautiful combination of Greek and Latin that means “tyrant lizard king”—and put the bones on display at the American Museum, as the institution is known among scientists. The new dinosaur became a sensation, making headlines throughout the country. The New York Times celebrated it as “the most formidable fighting animal” that had ever existed. Crowds flocked to the museum, and when they came face-to-face with the tyrant king, they were aghast at its monstrous size and dumbfounded by its ancient age, then estimated at some 8 million years old (we now know that it is much older, about 66 million years old). T. rex had become a celebrity, and so had Barnum Brown. Brown will always be remembered as the man who discovered Tyrannosaurus rex, but this was just the start of his career. He developed such an eye for fossils that he steadily progressed from a fossil-collecting grunt worker to the curator of vertebrate paleontology at the American Museum, the scientist in charge of the world’s finest dinosaur collection. Today, if you visit its spectacular dinosaur halls, many of the fossils you’ll see were collected by Brown and his teams. No wonder that Lowell Dingus, one of my former colleagues in New York who wrote a biography of Brown, refers to him as “the best dinosaur collector who ever lived.” This sentiment is shared by many of my fellow paleontologists. Brown was the first celebrity paleontologist, acclaimed for his lively lectures and a weekly CBS radio show. People would flock to see him as he passed through the American West on trains, and later in his life he helped Walt Disney design the dinosaurs in Fantasia. Like any good celebrity, Brown was an eccentric. He hunted fossils in the dead of summer in a full-length fur coat, made extra cash spying for governments and oil companies, and had such a fondness for the ladies that rumors of his tangled web of offspring are still whispered throughout the western American plains. You can’t help but think that if Brown were alive today, he would be the star of some outrageous reality show. And probably a politician. A few years after T. rex stormed New York, Brown was back at it, in his fur coat, scrambling over the badlands of Montana, looking for more fossils. As usual, he found them. This time it was a much better Tyrannosaurus: a more complete skeleton with a gorgeous skull, nearly as long as a man and with over fifty sharp teeth the size of railroad spikes. While Brown’s first T. rex was too scrappy to make a good estimate for the total size of the animal, the second fossil showed that rex was a king indeed: a dinosaur well over thirty-five feet long that must have weighed several tons. There was no doubt: T. rex was the largest and most fearsome land-living predator that had ever been discovered.


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FOR THE NEXT few decades, T. rex enjoyed life at the top, the star of movies and museum exhibits around the globe. It battled the giant gorilla in King Kong and terrified audiences in the screen adaptation of Arthur Conan Doyle’s The Lost World. But this fame masked a puzzle: for nearly the entire twentieth century, scientists had little idea of how T. rex fit into the broader picture of dinosaur evolution. It was an oddball, a creature so much larger and so dramatically different from other known predatory dinosaurs that it was difficult to place in the dinosaur family album. During the first few decades after Brown’s discovery, paleontologists unearthed a handful of close T. rex relatives in North America and Asia. To nobody’s surprise, Brown himself made some of the most important of these discoveries, most notably a mass graveyard of big tyrannosaurs in Alberta in 1910. These T. rex cousins—Albertosaurus, Gorgosaurus, Tarbosaurus—are quite similar to T. rex in size and have nearly identical skeletons. As the science of dating rocks advanced during the later twentieth century, it was also determined these other tyrannosaurs lived at about the same time as T. rex: the very latest Cretaceous, between 84 and 66 million years ago. So scientists were in a quandary. There were a bunch of huge tyrannosaurs at the top of the food chain thriving at the peak of dinosaur history. Where did they come from? That mystery has been answered only very recently, and as with so much of what we’ve learned about dinosaurs over the last few decades, our new understanding of tyrannosaur evolution stems from a wealth of new fossils. Many of these have come from unexpected locales, perhaps none more so than what is currently recognized as the very oldest tyrannosaur, a modest little critter called Kileskus that was discovered in 2010 in Siberia. When you think of dinosaurs, Siberia is probably not a place that comes to mind, but their fossils are now being found throughout the world, even the far northern reaches of Russia, where paleontologists need to cope with harsh winters and humid, mosquito-infested summers. Alexander Averianov, my friend from the Zoological Institute of the Russian Academy of Sciences in Saint Petersburg, is one of those paleontologists. Sasha, as we all call him, is among the world’s experts on those puny mammals that lived alongside (or more correctly, underneath) the dinosaurs. He also studies the dinosaurs that were keeping his beloved mammals down. Sasha began his career as the Soviet Union was disintegrating, and through his numerous discoveries and meticulous descriptions of fossil anatomy, he has now become one of the leading paleontologists in the new Russia. A few years ago, Sasha showed me a new dinosaur fossil from Uzbekistan at a conference. He whisked me up to his room, ceremoniously opened an ornately colored orange-and-green cardboard box, and pulled out part of the skull of a meat-eater.


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He put the fossil back in the box and handed it to me so I could take it back to Edinburgh to CAT-scan it. But before he let go, he looked me in the eye and, in the Russian-accented drawl of movie bad guys, said, “Be careful with the fossil, but be even more careful with the box. This is Soviet box. They don’t make them like this anymore.” Grinning with mischief, he then pulled out a small bottle of dark-colored liquid. “And now we toast with Dagestan cognac,” he proclaimed, pouring two glasses, then another two, and then a third round. We toasted to his tyrannosaurs. Like Brown’s first fossil of Tyrannosaurus rex, Sasha’s dinosaur Kileskus was only a fraction of a skeleton. There was part of the snout and the side of the face, a tooth, a chunk of the lower jaw, and some random bones from the hand and feet. These bones were all found within a couple of square meters in a quarry that Sasha’s team had been working in for many years, in the Krasnoyarsk region of central Siberia. Krasnoyarsk is one of the more than eighty “federal subjects” of Russia, as the post-Soviet constitution calls the equivalents to American states or Canadian provinces. It’s no little Delaware, or even Texas, or incredibly, even Alaska. Krasnoyarsk stretches across nearly the entire midsection of Russia, from the Arctic Sea up north to almost touch the border with Mongolia down south. It’s a shade below one million square miles in area, much bigger than Alaska and even slightly larger than Greenland. A lot of space, but very few people: the entire population is about the same as Chicago’s. In this vast wilderness, Sasha was able to find the world’s oldest tyrannosaur. The name he gave it, Kileskus, is based on the word “lizard” in a local language that is spoken by only a few thousand people in this isolated part of the world. The discovery didn’t get much buzz in the press, and it escaped the attention of many scientists when Sasha described it in an obscure Russian journal that isn’t on the radar of most paleontologists. Kileskus didn’t get a funny nickname, and it surely won’t be appearing in any future Jurassic Park films. It’s one of those fifty-some new dinosaurs that are announced in a technical scientific paper every year and then mostly forgotten about, except by a handful of specialist paleontologists. To me, though, Kileskus is one of the most interesting discoveries of the last decade, because it is clear proof that tyrannosaurs had gotten an early evolutionary start. Kileskus was found in rocks formed during the middle part of the Jurassic Period, about 170 million years ago, more than 100 million years before T. rex and its colossal cousins were at the top of their game in North America and Asia. Kileskus may be important, but it is underwhelming to behold.


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I first scrutinized the bones in Sasha’s dark office, in a grand old building along the icy Neva River, which was still thawing in early April. Yes, Sasha’s fossil is only a few bones, but that’s not too surprising. The vast majority of new dinosaur discoveries are just a few jumbled pieces of bone, because it takes a whole lot of luck for even a tiny fraction of a skeleton to withstand millions of years buried in the ground. No, what struck me about Kileskus was how small it is. All of the bones can comfortably fit into a couple of shoeboxes. I could easily lift them up off the shelf. If I wanted to pick up the skull of T. rex back in New York, I would need a forklift. It’s hard to believe that a meek creature like Kileskus could have given rise to a giant like T. rex. Although an accurate measure of its size is difficult because of its scrappy bones, Kileskus was probably only seven or eight feet long, most of that being the skinny tail. It stood a couple of feet tall at most—it would have come up to your waist or chest like a big dog. And it wouldn’t have weighed more than a hundred pounds or so. If the forty-foot-long, ten-foot-tall, seven-ton T. rex was living in Russia during the Middle Jurassic, it could have brushed Kileskus aside with little effort, even with its pathetic little arms. Kileskus was not a brutish monster. It wasn’t a top predator. It was probably something like a wolf or jackal, a long-legged, lightweight hunter that used speed to chase down small prey. It’s surely no coincidence that the quarry in Krasnoyarsk where Kileskus was found is bursting with the fossils of small lizards, salamanders, turtles, and mammals. It was these things that the very first tyrannosaurs were eating, not long-necked sauropods or jeep-size stegosaurs. Because Kileskus is so different from T. rex in size and hunting habits, how do we know that it’s even a tyrannosaur? If Kileskus had been discovered at the same time as T. rex, scientists probably wouldn’t have made the connection. Even if Kileskus had been found a few decades ago, it likely wouldn’t have registered as a primitive tyrannosaur, a great-great-great-grandparent of T. rex. Now we know, and once again, it’s because of new fossils. Sasha had the great fortune of finding Kileskus just four years after a team in far western China, led by my colleague Xu Xing, came across a very similar small meat-eater from the middle part of the Jurassic. Thankfully, Xu’s team didn’t just find a couple of broken bones. They uncovered two nearly complete skeletons, one an adult and the other a teenager. The story of how these dinosaurs got there could be written into the script of a disaster movie. The teenager was found at the bottom of a pit several feet deep, trampled by the adult.


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They were both engulfed in mud and volcanic ash. Something terrible had clearly happened, but what was torture for these dinosaurs was a lucky break for paleontologists. Xu and his group named their new dinosaur Guanlong, meaning “crown dragon” in Chinese. The name refers to the gaudy Mohawk-like crest of bone that runs along the top of the skull. The crest is thinner than a dinner plate and pierced by a number of holes. It’s the type of absurdly impractical-looking thing that probably had only one function: a display ornament for attracting mates and intimidating rivals, kind of like the flamboyant tail of a male peacock, which is for nothing but show. I spent days poring over the bones of Guanlong in Beijing. The crest is what grabbed my attention first, but other features of the bones offer critical clues for placing Guanlong on the family tree and linking it to both Kileskus and T. rex. For a start, it is clearly very similar to Kileskus: both are about the same size, have huge windowlike nostrils at the front of the snout, and have long upper-jaw bones with a deep depression above the teeth that would have housed a huge sinus. On the other hand, Guanlong exhibits many characteristics that are only seen in T. rex and other big tyrannosaurs among all of the meat-eating dinosaurs. In other words, evolutionary novelties, which as we learned earlier, are the key to understanding genealogy. For example, it has heavily fused nasal bones at the top of the snout, a broad and rounded front of the snout, a small horn in front of the eye, and two massive muscle attachment scars on the front of the pelvis. There are many more similarities as well, anatomical minutiae that may seem boring but tell my scientific colleagues and me that Guanlong is definitively a primitive tyrannosaur. And because the complete skeletons of Guanlong share so many features with the much scrappier bones of Kileskus, the latter must be a primitive tyrannosaur as well. Along with helping to prove that Kileskus is a tyrannosaur, the complete skeletons of Guanlong also paint a clearer picture of what these earliest and most primitive tyrannosaurs would have looked like, how they behaved, and how they fit into their ecosystems. Based on its limb dimensions—which are known to correlate closely with body weight in living animals—Guanlong would have weighed about 70 kilograms, or roughly 150 pounds. Guanlong was lithe and lean, with long skinny legs and a tail that stretched far beyond its body for balance. No doubt it was a speedy hunter. It had a mouth full of steak-knife-like teeth befitting a predator, but it also had fairly long arms with three claw-capped fingers capable of grabbing prey with extreme strength. They are totally different from the withered two-fingered arms of T. rex. Guanlong could hunt with its arsenal of speed, sharp teeth, and deadly claws, but it was not a top predator.


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It lived alongside much larger carnivores like Monolophosaurus, which was over fifteen feet long, and Sinraptor, a thirty-foot-long close cousin of Allosaurus that weighed more than a ton. Guanlong lived in the shade of these animals, and probably in fear of them too. At best, Guanlong was a second- or third-tier predator, an inconspicuous link in a food chain dominated by other dinosaurs. This would have been the same for Kileskus and for some of the other small and primitive tyrannosaurs that have been found recently, like the tiniest one of all, the greyhound-size Dilong from China, and Proceratosaurus, a dinosaur discovered over a century ago in England that was only recently recognized as an archaic tyrannosaur because it has a Mohawk-like crest similar to Guanlong. These petite tyrannosaurs may not have been much to look at and wouldn’t have haunted anyone’s nightmares, but they obviously were doing something right. The more fossils we find, the more successful we realize they were. There were a bunch of them, spread all over the world during the approximately 50 million years from the middle part of the Jurassic period well into the Cretaceous, from about 170 until 120 million years ago. They clearly survived that cocktail of environmental and climate changes that felled Allosaurus, the sauropods, and the stegosaurs around the Jurassic-Cretaceous boundary. We now have their fossils from throughout Asia, multiple sites in England, the western United States, and probably even Australia. They were able to disperse so widely because they lived when the supercontinent Pangea was still breaking apart, meaning they could easily hop across land bridges that linked the continents, which had yet to move very far away from one another. These early tyrannosaurs had carved out a niche as small to midsize predators living in the underbrush, and they were good at it. The skeleton of the dog-size primitive tyrannosaur Dilong. Photo courtesy of the author The skull of the human-size primitive tyrannosaur Guanlong, showing the gaudy crest of bone on top of its head. Photo courtesy of the author AT SOME POINT, however, tyrannosaurs changed from bit players to the celebrated apex predators that we all love. The first whispers of this transformation are seen in fossils from the early part of the Cretaceous, about 125 million years ago. Most tyrannosaurs living at this time were small. The pint-size Dilong is the most extreme example, barely registering on the scales at about twenty pounds. Some were a bit larger, like Eotyrannus from England and a few of its older cousins like Juratyrant and Stokesosaurus, which were bulkier than Dilong, Guanlong, and Kileskus, and maybe reached lengths of about ten to twelve feet and weights of a thousand pounds or so. If you were around back then, and these midsize tyrannosaurs cooperated, you could have ridden them like horses, but they still weren’t top-of-the-food-chain animals.


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Then in 2009, another piece of the puzzle: a team of Chinese scientists described a highly unusual fossil from the northeastern corner of the country, which they called Sinotyrannus. As is so often the case, the new dinosaur was fragmentary: only a small collection of bones was preserved, including the front of the snout and lower jaw, some portions of the backbone, and a few pieces of the hand and pelvis. These bones were really similar to Guanlong, and also to Kileskus, which would be described a few months later. The base of a tall bony crest was visible right where the snout region was broken, the nostril opening was huge, and there was a deep sinus depression above the teeth. But there was one major difference: Sinotyrannus was substantially bigger than Guanlong. Based on comparisons to the bones of other meat-eating dinosaurs, it was estimated that this new predator would have been around thirty feet long, and perhaps over a ton in weight. That’s the equivalent to at least ten Guanlongs. At about 125 million years in age, Sinotyrannus was the oldest example of a large-bodied tyrannosaur ever found. I read the announcement of the new species as a graduate student, about a year after I began my PhD project on carnivorous dinosaur evolution. It was clear to me that the new dinosaur was a tyrannosaur and that it was big, but I didn’t know what else to make of it. The fossils were too scrappy to be certain of how large it was or to place it accurately in the family tree. Was it a very close relative of T. rex, the first member of that group of really big, deep-skulled, tiny-armed carnivores—Tyrannosaurus, Tarbosaurus, Albertosaurus, Gorgosaurus—that dominated the very end of the Cretaceous, about 84 to 66 million years ago? If so, maybe it would tell us how these dinosaur icons became so huge, so dominant. But was it something else? Maybe it was merely a primitive tyrannosaur that outgrew its contemporaries. After all, Sinotyrannus lived about 60 million years before T. rex, a time when every other tyrannosaur we knew of could fit in the back of a pickup truck. Could this one find really rewrite tyrannosaur history? I had the sinking feeling that this fossil would remain a problem for a long time. This happens all too often in the field of dinosaur research: a single fossil emerges that hints at a major evolutionary story—the oldest member of a major group, or the first fossil to exhibit a really important behavior or feature of the skeleton—but it’s too broken or incomplete or poorly dated to be certain. Then another fossil is never found and it’s just left hanging, a cold case waiting to be solved. The skull of Gorgosaurus, a large-bodied, latest Cretaceous tyrannosaur closely related to T. rex. Photo courtesy of the author But I shouldn’t have been so pessimistic.


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Just three years later, Xu Xing in China—the man who described Guanlong and Dilong—published a sensational article in the journal Nature. Xu and his team announced yet another new dinosaur, which they called Yutyrannus. They had more than just a few bones at their disposal—they had skeletons, three of them. Their new dinosaur was obviously a tyrannosaur and was very similar to Sinotyrannus. There were similarities in size and also in the bones—Yutyrannus had a flashy head crest and huge nostrils, just like Sinotyrannus. Yutyrannus was big: the largest skeleton was about thirty feet long. This wasn’t an estimate, because Xu and his team could take out a tape measure and size up their new dinosaur, rather than using mathematical equations to guesstimate the size of a complete skeleton based on just a few broken bones, as was our only recourse with Sinotyrannus. So Yutyrannus sealed the deal: there really were large tyrannosaurs in the Early Cretaceous, at least in China. There was something else peculiar about Yutyrannus. The skeletons were so well preserved that details of the soft tissue were visible. Usually the skin, muscles, and organs decay away long before a fossil is entombed in stone, leaving only the hard parts like bones, teeth, and shells. With Yutyrannus we got lucky—these skeletons were buried so quickly, after a volcanic eruption, that some of their softer parts did not decay. Packed all around the bones were dense clusters of slender filaments, each about fifteen centimeters (six inches) long. Similar structures were preserved on the much smaller Dilong, which was found in the same rock unit in northeastern China. These are feathers. Not the quill-pen feathers that make up the wings of today’s birds but simpler ones that look more like strands of hair. These were the ancestral structures that bird feathers evolved from, and it is now known that many (and perhaps all) dinosaurs had them. Yutyrannus and Dilong establish beyond a doubt that tyrannosaurs were among these feathered dinosaurs. Unlike birds, tyrannosaurs certainly were not flying. Instead, they probably used their feathers for display or to keep warm. And because both a large tyrannosaur like Yutyrannus and a small tyrannosaur like Dilong have feathers, this implies that the common ancestor of all tyrannosaurs had feathers, and therefore that the great T. rex itself was most likely feathered, too. The fluff-covered skeletons of Yutyrannus launched this new dinosaur to stardom in the international press, but feathers are a story that we’ll come back to later. For me, the real importance of Yutyrannus was that it could help us better understand how tyrannosaurs evolved into their huge sizes. Yutyrannus and Sinotyrannus were big—much larger than any other tyrannosaurs living before the very end of the Cretaceous, when T. rex and its brethren reigned supreme.


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However, these two Chinese tyrannosaurs weren’t truly colossal: they were about the same size as Allosaurus or the big predator Sinraptor that preyed on Guanlong, nowhere near the monstrous forty-foot-long, seven-ton body sizes of T. rex and its very close relatives. Not only that, but when the complete skeletons of Yutyrannus are compared bone by bone with the skeletons of T. rex, it becomes clear they are quite different. Yutyrannus looks like an overgrown version of Guanlong, with its ornamental head crest, big nostrils, and long, three-fingered hands. It doesn’t have the deep muscular skull, thick railroad-spike teeth, and pathetic arms of T. rex. This leads to an unexpected conclusion: despite their big bodies, Yutyrannus and Sinotyrannus weren’t very closely related to T. rex, and they didn’t have much to do with the evolution of colossal sizes in the latest Cretaceous tyrannosaurs. Instead, they were primitive tyrannosaurs experimenting with large body sizes independent of their later cousins. Put another way, they were evolutionary dead ends that, as far as we know, didn’t exist outside of one corner of China during the early Cretaceous. (This assertion can of course be proven wrong with new discoveries.) They lived alongside small tyrannosaurs, which were by far the more common type thriving in the Jurassic and early Cretaceous times. Even though they were not directly ancestral to T. rex, Yutyrannus and Sinotyrannus are far from unimportant. These early Cretaceous species do show that tyrannosaurs had the capability to become big fairly early in their evolution. Yutyrannus and Sinotyrannus were, as far as we know, the largest predators in their ecosystems. They were at the top of the food chain, the lords of a lush forest—humid in the summer, liable to be buried by snow in the winter—that clung to the sides of steep volcanoes, alive with the chirps of primitive birds and raptor dinosaurs with feathers. They had their choice of prey: corpulent long-necked sauropods if they were feeling particularly hungry, or a bounty of sheep-size, beaked plant-eaters called Psittacosaurus, primitive cousins of Triceratops, which 60 million years later would battle T. rex itself on the floodplains of western North America. In other places, separated in time and space from the forests of Early Cretaceous China, where the species of tyrannosaurs were small or medium-size, they were dwarfed by larger predators. Sinraptor towered over Guanlong in the Middle Jurassic of China. Allosaurus outmuscled the mule-size tyrannosaur Stokesosaurus in the later Jurassic of North America. The carcharodontosaur Neovenator held down Eotyrannus in the Early Cretaceous of England. And there are many more examples. It seems tyrannosaurs could get big if they had the opportunity, but only if there were no larger predators around. THE QUESTION REMAINS: how did T. rex and its closest relatives shoot up to such mind-boggling sizes? We need to look into the fossil record to see when the very first truly huge tyrannosaurs with the classic T. rex body plan emerged.


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By this, I mean tyrannosaurs that were over thirty-five feet long and one and a half tons in weight, with the big deep skulls, muscular jaws, banana-size teeth, pathetic arms, and bulky leg muscles that define T. rex. This type of tyrannosaur—true giants, undoubted top predators of record size—made their first appearance in western North America about 84 to 80 million years ago. Once they began to appear, they started turning up everywhere, both in North America and Asia. Clearly an explosive diversification had occurred. We know that the big switch happened some time in the middle part of the Cretaceous, between about 110 and 84 million years ago. Before this time, there were many small to midsize tyrannosaurs living all over the world, with only a few random bigger species like Yutyrannus. After this time, enormous tyrannosaurs reigned throughout North America and Asia, but only those continents, and no species smaller than a minibus remained. This was a dramatic change, one of the biggest in the entire history of dinosaurs. Frustratingly, very few fossils record what was going on. The middle Cretaceous is something of a dark period in dinosaur evolution. By pure bad luck, very few fossils from this entire 25-million-year time span have been found. So we’re left scratching our heads, like a detective tasked with solving a crime when the crime scene preserves no fingerprints, DNA data, or tangible evidence of any kind. What we can say, based on our growing understanding of what the Earth was like during the middle Cretaceous, is that this was probably not a great time to be a dinosaur. About 94 million years ago, between the Cenomanian and Turonian subdivisions of the Cretaceous Period, there was a spasm of environmental change. Temperatures spiked, sea levels violently oscillated, and the deep oceans were starved of oxygen. We don’t yet know why this happened, but one of the leading theories is that a surge of volcanic activity belched enormous quantities of carbon dioxide and other noxious gases into the atmosphere, causing a runaway greenhouse effect and poisoning the planet. Whatever their causes, these environmental changes triggered a mass extinction. It wasn’t as big as the extinctions at the ends of the Permian and Triassic periods, which helped dinosaurs rise to dominance, but something more akin to what happened across the Jurassic-Cretaceous boundary. Still, it was one of the worst mass die-offs during the Age of Dinosaurs. Many ocean-living invertebrates disappeared for good, as did various types of reptiles. The extremely poor middle Cretaceous fossil record has made it difficult to know how these environmental dramas affected dinosaurs. However, paleontologists have recently managed to pry important new specimens from this gap. A pattern is clearly coming into focus: none of the large predators from this 25-million-year time window are tyrannosaurs. All of them belong to other groups of big carnivores like the ceratosaurs, spinosaurs, and especially the carcharodontosaurs.


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This latter group of ultrapredators, which (as we saw in the previous chapter) utterly dominated the Early Cretaceous, continued their reign deep into the middle Cretaceous. The thirty-five-foot-long carcharodontosaur Siats was the top predator in western North America about 98.5 million years ago. In Asia, the nearly T. rex–size Chilantaisaurus and the smaller Shaochilong were the top guns about 92 million years ago, and in South America, carcharodontosaurs like Aerosteon reigned about 85 million years ago. The tyrannosaurs that lived alongside these carcharodontosaurs, on the other hand, still weren’t very special, at least in their outward appearance. We don’t have many of their fossils, but some have started to turn up recently. The best of them come from Uzbekistan, where Sasha Averianov and his colleague Hans-Dieter Sues—a German-born paleontologist with an ever-present smile and infectious laugh, who is now a senior researcher at the Smithsonian Institution—worked for over a decade, in the barren Kyzylkum Desert. That Soviet-era box that Sasha carefully handed over to me a few years ago contained some of these bones. The reason I took them back to Edinburgh to CAT-scan was because two of these specimens were braincases—the puzzle of fused bones at the back of the skull that surrounded the brain and ear. If you want to see inside these braincases, into the cavities that housed the brain and sense organs, you could cut open the braincase with a saw, which is what Osborn did with the first T. rex skull, damaging it forever in the name of science. Nowadays we can use the CAT scanner and its high-powered X-rays, and we don’t have to damage a thing. When we scanned the Uzbek braincases, we confirmed that they belonged to a tyrannosaur, as they had the same architecture of bones surrounding the spinal cord and the same long tube-shaped brain cavity of T. rex, Albertosaurus, and other tyrannosaurs. They even had a middle ear with a very long cochlea, another signature tyrannosaur feature, which allowed these predators to better hear low-frequency sounds. However, the Uzbek tyrannosaur was still a Mini-Me, just about the size of a horse. In spring 2016, Sasha, Hans, and I gave the Uzbek tyrannosaur a formal scientific name, Timurlengia euotica. The name honors Timur, also known as Tamerlane, the infamous Central Asian warlord who ruled over Uzbekistan and many of the surrounding lands in the fourteenth century. It’s a fitting name for a tyrannosaur, even a midsize one that was still a few rungs below the top of the food ladder. Although not a colossus, Timurlengia was developing a larger brain and more sophisticated senses—heightened smell, vision, and hearing—than other meat-eating dinosaurs, adaptations that would eventually turn out to be handy predatory weapons for the huge tyrannosaurs that came later. Tyrannosaurs were becoming smart before they got big, but no matter how clever they were, Timurlengia and its comrades were still living under the thumb of the real warlords of the middle Cretaceous, the carcharodontosaurs.


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Then, when the clock struck 84 million years ago and the fossil record became rich again, the carcharodontosaurs were gone in North America and Asia, replaced by monstrous tyrannosaurs. A major evolutionary turnover had occurred. Was this due to the lingering effects of the temperature and sea-level changes that occurred at the Cenomanian-Turonian boundary? Was it sudden or gradual? Did tyrannosaurs actively outcompete the carcharodontosaurs, muscling them into extinction or outsmarting them with their big brains and keenly developed senses? Or did environmental changes cause these other large predators to go extinct but spare tyrannosaurs, which then opportunistically took over the large predator role? We just don’t have enough evidence to know for certain, but whatever the answer, there is no denying that by the dawn of the Campanian subinterval of the latest Cretaceous, beginning about 84 million years ago, tyrannosaurs had risen to the top of the food pyramid. During the final 20 million years of the Cretaceous, tyrannosaurs flourished, ruling the river valleys, lakeshores, floodplains, forests, and deserts of North America and Asia. There is no mistaking their signature look: huge head, athletic body, sad arms, muscular legs, long tail. They bit so hard that they crunched through the bones of their prey; they grew so fast that they put on about five pounds every day during their teenage years; and they lived so hard that we have yet to find an individual that was more than thirty years old when it died. And they were impressively diverse: we have found nearly twenty species of these big-boned tyrannosaurs from the latest Cretaceous, and there are surely many more out there waiting to be discovered. The Pinocchio-nosed Qianzhousaurus, so fortuitously discovered by that still-anonymous backhoe operator at the Chinese construction site, is one of the latest examples. Just as Brown and Osborn grasped over a hundred years ago, when they were the first humans to set eyes on a tyrannosaur, T. rex and its brethren really were the kings of the dinosaur world. The world they lorded over was very different from the planet in which tyrannosaurs grew up. Back when Kileskus, Guanlong, and Yutyrannus were stalking prey, the supercontinent Pangea had only recently begun to split, so tyrannosaurs could migrate easily across the Earth. By the latest Cretaceous, however, the continents had drifted much farther apart, reaching positions similar to the ones they occupy today. A map from this time would have looked quite a bit like today’s globe. There were, however, some major differences. Due to sea-level rise in the Late Cretaceous, North America was bisected by a seaway stretching from the Arctic to the Gulf of Mexico, and a flooded Europe was reduced to a smattering of small islands. T. rex’s Earth was a fragmented planet, with different groups of dinosaurs living in separate areas. As a result, champions in one region might not be able to conquer another for one simple reason: they couldn’t get there.


The rise and fall of the dinosaurs [eBook - NC Digital -- Steve Brusatte -- 1, 2018 -- William Morrow -- 9780062490421 -- 819b642fffa68675f9e07cf3af773125 -- Anna’s Archive.18

Colossal tyrannosaurs never seemed to gain a foothold in Europe or the southern continents, where other groups of large predators prospered, but in North America and Asia, tyrannosaurs were unrivaled. They had become the transcendent terrors that fire our imaginations.