The Rise and Fall of the Dinosaurs: A New History of a Lost World: The Definitive Dinosaur Encyclopedia with Stunning Illustrations, Embark on a Prehistoric Quest!

by Steve Brusatte

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.

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.

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.

rex’s Earth was a fragmented planet, with different groups of dinosaurs living in separate areas.

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.

rex was huge: adults were about forty-two feet (thirteen meters) long and weighed in the ballpark of seven or eight tons,

Like a ballerina, it balanced on the tips of its feet, the arch or sole rarely touching the ground, all of its weight held by its massive three toes.

The forelimbs looked useless: puny things with two stubby fingers, comically out of proportion to the rest of the body.

five feet long from snout to ear, the skull was nearly the length of an average person.

More than fifty knife-sharp teeth

Each eyeball was the size of a grapefruit.

Covering the body—the head, the wee arms, the stocky legs, all the way to tip of the tail—was a thick, scaly hide.

rex resembled an overgrown crocodile or an iguana—lizardlike. But there was one key difference: Rex also had feathers sticking out from between its scales.

these were not big branching ones like those on a bird wing, but were simpler filaments that looked and felt more like hair, the larger one...

feathers started out as simple wisps of integument, which creatures like T. rex used to keep warm, and as displays to attract mates and scare off rivals.

Paleontologists have yet to find any fossilized feathers on a T. rex skeleton, but we’re confident that it must have had some fluff because primitive tyrannosaurs—Dilong and Yutyrannus,

T. rex lived from about 68 to 66 million years ago, and its dominion was the forest-covered coastal plains and river valleys of western North America.

lorded over diverse ecosystems that included a bounty of prey species: the horn-faced Triceratops, the duck-billed Edmontosaurus, the tanklike Ankylosaurus, the dome-headed Pachycephalosaurus,

rex, as it turns out, was an immigrant. It got its start in China or Mongolia, hopped across the Bering Land Bridge, journeyed through Alaska and Canada, and made its way down into the heart of what’s now America.

invasive pest that spread all the way from Canada down to New Mexico and Texas, elbowing out all of the other midsize to large predatory dinosaurs so that it alone controlled an entire continent.

rex was there when the asteroid fell down from the sky 66 million years ago, putting a violent end to the Cretaceous, exterminating all of the nonflying dinosaurs.

the King went out on top, cut down at the peak of its power.

bones have been found preserved in the stomach area of tyrannosaur skeletons

Rex needed to gobble up some 250 pounds (about 111 kilograms) of grub each and every day.

Rex clamped down hard enough to literally break through the bones of its prey.

Bone crunching is not normal—some mammals, like hyenas, do it, but most modern reptiles do not. As far as we know, big tyrannosaurs like T. rex were the only dinosaurs capable of it.

The thick, peglike teeth were strong enough that they wouldn’t easily break when they hit bone. Next, consider the power behind those teeth: T. rex’s jaw muscles were massive, bulging mounds of sinew that provided enough energy to shatter the limbs, backs, and necks of Triceratopses, Edmontosauruses, and other prey. We can tell that Rex had some of the largest and most powerful jaw muscles of any dinosaur, based on the very broad and deep gullies on the skull bones where the muscles attached.

of the most famous dinosaur in history. T. rex bit so hard it could crunch through the bones of its prey, it was so bulky that it couldn’t run fast as an adult, it grew so fast as a teenager that it put on five pounds a day for a decade, it had a big brain and sharp senses, it hung around in packs, and it was even covered in feathers.

Rex had feathers, grew rapidly, and even breathed like a bird. Dinosaurs were not alien creatures.

Each landmass had a unique suite of dinosaurs—its own megapredators, second-tier hunters, scavengers, big and small herbivores, and omnivores. Provinciality extended to other species as well: there were distinct types of crocodiles, turtles, lizards, frogs, and fishes on the various parcels of land, and of course, different types of plants too. In this way, isolation bred diversification.

species are not fixed entities; they evolve over time. He even had a mechanism to explain evolution, a process he called natural selection.

All populations of organisms are variable in their features. For instance, if you look at a bunch of rabbits in nature, they will have slightly different fur colors, even if they all belong to the same species. Sometimes one of those variations confers a survival advantage—say, darker fur that helps a rabbit camouflage itself better—and because of that, the individuals with that feature have a better chance of living longer and reproducing more. If that variation is heritable—if it can be passed on to offspring—then over time it will cascade throughout the population so that the entire rabbit species is now dark-haired. Dark hair has been naturally selected, and the rabbits have evolved.

This process can even produce new species: if a population is somehow divided and each subset goes its own way, evolving its own naturally selected features until the two subsets are so different that they’re unable to reproduce with each other, they have developed into separate species.

Evolution by natural selection is also what produced us, and don’t be mistaken, it continues to operate right now, constantly, all around us. It’s why we’re so worried about superbugs that evolve resistance to antibiotics, why we’re always in need of new medicines to stay a step ahead of the bacteria and viruses that will do us harm.

how evolution produces radically new groups of organisms, with restyled bodies capable of remarkable new behaviors. The formation of small, fast-growing, warm-blooded, flying birds from ancestors that looked like T. rex and Allosaurus is a prime example of this sort of jump—what biologists call a major evolutionary transition.

Birds are a type of theropod; they are rooted in that group of ferocious meat-eaters that most famously includes T. rex and Velociraptor

many features are shared uniquely by birds and other theropods: not just feathers, but also wishbones, three-fingered hands that can fold against the body, and hundreds of other aspects of the skeleton.

There are no other groups of animals—living or extinct—that share these things with birds or theropods: this must mean that birds came from theropods.

Today’s birds stand out among all modern animals. Feathers, wings, toothless beaks, wishbones, big heads that bob along on an S-shaped neck, hollow bones, toothpick legs . . .

This body plan is behind the many superskills that birds are so renowned for: their ability to fly, their hypercharged growth rates, their warm-blooded physiology, and their high intelligence and sharp senses.

many of the supposedly signature features of today’s birds—the components of their blueprint—first evolved in their dinosaur ancestors. Far from being unique to birds, these features developed much earlier, in ground-living theropods, for reasons wholly unrelated to flight.

Long, straight legs and feet with three skinny main toes—hallmarks of the modern bird silhouette—first appeared more than 230 million years ago in the most primitive dinosaurs, as their bodies were reshaped into upright-walking, fast-running engines that could outpace and outhunt their rivals.

some of these upright-walking dinosaurs—the earliest members of the theropod dynasty—fused their left and right collarbones into a new structure, the wishbone.

subset of these small, upright, wishboned, bobbing-necked theropods started to fold their arms against the body, probably to protect the delicate quill-pen feathers that were evolving around the same time. These were the paravians—a subgroup of the maniraptorans, and the immediate ancestors of birds.

many of the features that allow me to immediately recognize it as a bird are not actually trademarks of birds. They’re attributes of dinosaurs.

today’s birds use their wings for many things other than flying (which is why, for instance, flightless birds like ostriches don’t lose their arms entirely). They are also used as display structures to entice mates and frighten rivals, as stabilizers that help birds climb, as fins to help them swim, and as blankets for keeping eggs warm in the nest, along with many other functions. Wings could have evolved for any of these reasons—or maybe another function entirely—but display seems the most likely, and there is growing evidence for it.

The totality of the evidence—that wings first evolved in dinosaurs too large and ungainly to fly, that these wings were ornately colored, and that modern birds use their wings for display—has led to a radical new hypothesis. Wings originally evolved as display structures—as advertising billboards projecting from the arms, and in some cases, like Microraptor, the legs, and even the tail.

Flight probably evolved many times in parallel, as different species of these dinosaurs—with their different airfoil and feather arrangements—found themselves generating lift from their wings as they leaped from the ground, scurried up trees, or jumped between branches.

The culmination of this long transition was a game-changer in the history of life. When evolution had finally succeeded in assembling a small, winged, flying dinosaur, a great new potential was unlocked. These first birds began to diversify like crazy, probably because they had evolved a new ability that allowed them to invade novel habitats and live a different lifestyle than their predecessors. We can see this (relatively) sudden change in the fossil record.

Many birds lived during the Age of Dinosaurs. The first flapping fliers must have originated sometime before 150 million years ago, because that is the age of Archaeopteryx, Huxley’s Frankenstein creature, which is still, as far as we know, the very oldest true bird, unarguably capable of powered flight, in the fossil record. Most likely, evolution had already assembled a small, winged, flapping, bona fide bird sometime in the middle part of the Jurassic Period, around 170 to 160 million years ago. That means there was a good hundred million years during which birds coexisted with their dinosaur predecessors.