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

Descriptions of the doom and gloom could go on for pages, but the point is, the end of the Permian was a very bad time to be alive. It was the biggest episode of mass death in the history of our planet. Somewhere around 90 percent of all species disappeared.

The Earth formed about 4.5 billion years ago, and the first microscopic bacteria evolved a few hundred million years later. For some 2 billion years, it was a bacterial world. There were no plants or animals, nothing that could easily be seen by the naked eye, had we been around. Then, some time around 1.8 billion years ago, these simple cells developed the ability to group together into larger, more complex organisms.

A global ice age—which covered nearly the entire planet in glaciers, down to the tropics—came and went, and in its aftermath the first animals got their start. They were simple at first—soft sacs of goo like sponges and jellyfish, until they invented shells and skeletons.

Around 540 million years ago, during the Cambrian Period, these skeletonized forms exploded in diversity, became extremely abundant, started eating one another, and began forming complex ecosystems in the oceans. Some of these animals formed a skeleton made of bones—these...

eventually some of them turned their fins into arms, grew fingers and toes, and emerged onto the land, about 390 million years ago. These were the first tetrapods, and their descendants include all vertebrates that live on land today: frogs and sal...

Walking upright, it seems, was one of the ways in which animals recovered—and indeed, improved—after the planet was shocked by the volcanic eruptions.

Very early, they split into two major lineages, which would grapple with each other in an evolutionary arms race over the remainder of the Triassic. Remarkably, both of these lineages survive today. The first, the pseudosuchians, later gave rise to crocodiles. As shorthand, they are usually referred to as the crocodile-line archosaurs. The second, the avemetatarsalians, developed into pterosaurs (the flying reptiles often called pterodactyls), dinosaurs, and by extension the birds that, as we shall see, descended from the dinosaurs. This group is called the bird-line archosaurs.

As one of the first dinosauromorphs, Prorotodactylus is something of a dinosaur version of Lucy, the famous fossil from Africa that belongs to a very humanlike creature but is not quite a true human, a member of our species, Homo sapiens. In the same way that Lucy looks like us, Prorotodactylus would have appeared and behaved very much like a dinosaur, but it’s simply not considered a true dinosaur by convention.

time between 240 and 230 million years ago.

The best way to figure out the age of rocks is to use a process called radiometric dating, which compares the percentages of two different types of elements in the rock—say, potassium and argon.

When a rock cools from a liquid into a solid, minerals form. These minerals are made up of certain elements, in our case including potassium. One isotope (atomic form) of potassium (potassium-40) is not stable, but slowly undergoes a process called radioactive decay, in which it changes into argon-40 and expels a small amount of radiation, causing the beeps you’d hear on a Geiger counter.

Beginning the moment a rock solidifies, its unstable potassium starts changing into argon. As this process continues, the accumulating argon gas becomes trapped inside the rock where it can be measured. We know from lab experiments the rate at which potassium-40 changes into argon-40. Knowing this rate, we can take a r...

But there is one major caveat: radiometric dating works only on rocks that cool from a liquid melt, like basalts or granites that solidify from lava.

The rocks that contain dinosaur fossils, like mudstone and sandstone, were not formed this way, but rather from wind and water currents that dumped sediment. Dating these types of rocks is much more difficult.

ALL UNCERTAINTIES ASIDE, we do know that by 230 million years ago, true dinosaurs had entered the picture.

The three major groups—the meat-eating theropods, long-necked sauropods, and herbivorous ornithischians—had

When the very first dinosaurs, like Herrerasaurus and Eoraptor, evolved from their cat-size dinosauromorph ancestors some 240 to 230 million years ago, there were no individual continents—no Australia or Asia or North America. There was no Atlantic Ocean separating the Americas from Europe and Africa, no Pacific Ocean on the flip side of the globe. Instead, there was just one huge solid unbroken mass of land—what geologists refer to as a supercontinent.

the supercontinent we call Pangea, and the ocean we call Panthalassa.

No better way to put it: the earliest dinosaurs lived in a sauna.

The Earth was a whole lot warmer back in the Triassic Period than it is today. In part, that’s because there was more carbon dioxide in the atmosphere, so more of a greenhouse effect, more heat radiating across the land and sea.

They entered a world still recovering from the terrible mass extinction at the end of the Permian, a land subject to the violent whims of storms and the blight of blistering temperatures. So did many other new types of plants and animals that were getting their start after the mass extinction cleared the planet. All of these newbies were thrust onto an evolutionary battlefield. It was far from certain that dinosaurs were going to emerge triumphant. After all, they were small and meek creatures, nowhere near the top of the food chain during their earliest years.

Absence of evidence is not always evidence of absence,

First, in the humid belt, the dominant large plant-eaters, the rhynchosaurs and dicynodonts, became less common. In some areas they disappeared entirely. We don’t yet fully understand why, but the consequences were unmistakable.

The second major breakthrough, around 215 million years ago, was that the first dinosaurs began arriving in the subtropical arid environments of the Northern Hemisphere, then about 10 degrees above the equator, now part of the American Southwest.

During the Late Triassic, there were many other animals that really, really looked and behaved like dinosaurs. In evolutionary biology speak, this is called convergence: different types of creatures resembling each other because of similarities in lifestyle and environment. It’s why birds and bats, which both fly, each have wings. It’s why snakes and worms, which both squirm through underground burrows, are both long, skinny, and legless.

Early in the Triassic, archosaurs split into two major clans: the avemetatarsalians, which led to dinosauromorphs and dinosaurs, and the pseudosuchians, which gave rise to crocodiles.

slaying their competitors, dinosaurs were being overshadowed by their crocodile-line rivals during the 30 million years they coexisted in the Triassic.

At the very end of the Triassic, 201 million years ago, the world was violently remade. For 40 million years, Pangea had been gradually splintering apart, and magma had been welling underground. Now that the supercontinent had finally cracked, the magma had somewhere to go. Like a hot-air balloon rising through the sky, the liquid-rock reservoir rushed upward, broke through the shattered surface of Pangea, and gushed out onto the land.

As with the volcanoes that had erupted at the end of the Permian Period some 50 million years earlier, causing the extinction that allowed dinosaurs and their archosaur cousins to get their start,

over a period of some six hundred thousand years, there were four big pulses of drama, when enormous amounts of lava would surge out of the Pangean rift zone like tsunamis from hell.

In all, some three million square miles of central Pangea were drowned in lava. It goes without saying that this was a bad time to be a dinosaur,

These things triggered one of the biggest mass extinctions in the history of life, a mass die-off that claimed over 30 percent of all species and maybe much more.

After some of the largest volcanic eruptions in Earth history desecrated ecosystems, dinosaurs became more diverse, more abundant, and larger. Completely new dinosaur species were evolving and spreading into new environments, while other groups of animals went extinct. As the world was going to hell, dinosaurs were thriving, somehow taking advantage of the chaos around them.

THE JURASSIC PERIOD marks the beginning of the Age of Dinosaurs proper. Yes, the first true dinosaurs entered the scene at least 30 million years before the Jurassic began. But as we’ve seen, these earlier Triassic dinosaurs had not even a remote claim to being dominant.

There were meat-eating theropods like Dilophosaurus, with a weird double-mohawk crest on its skull; at around twenty feet long, it was much larger than the mule-size Coelophysis and most other Triassic carnivores.

Some of the most famous dinosaurs of all are sauropods: Brontosaurus, Brachiosaurus, Diplodocus.

how did sauropods become so large? It’s one of the great puzzles of paleontology.

Recently, however, paleontologists have come up with two different approaches to more accurately predict the weight of a dinosaur based on its fossil bones.

The first is really quite simple and relies on basic physics: heavier animals require stronger limb bones to support their weight.

there is a basic equation that works for almost all living animals: if you can measure limb-bone thickness, you can then calculate body weight with a small but recognized margin of error—simple

The second method is more intensive but a lot more interesting. Scientists are starting to build three-dimensional digital models of dinosaur skeletons, add on the skin and muscles and internal organs in animation software, and use computer programs to calculate body weight.

The primitive proto-sauropods like Plateosaurus began to experiment with relatively large sizes in the Triassic, as some of them got up to about two or three tons in weight. That’s roughly equivalent to a giraffe or two. But after Pangea started to split, the volcanoes erupted, and the Triassic turned into the Jurassic, the true sauropods got much larger. The ones that left tracks in the Scottish lagoon weighed about ten to twenty tons, and later in the Jurassic, famous beasties like Brontosaurus and Brachiosaurus expanded to more than thirty tons. But that was nothing compared to some supersize Cretaceous species like Dreadnoughtus, Patagotitan, Argentinosaurus—members of an aptly named subgroup called the titanosaurs—which weighed in excess of fifty tons, more than a Boeing 737.

there was something intrinsic about sauropods that allowed them to break the shackles that constrained all other land animals—mammals, reptiles, amphibians, even other dinosaurs—to much smaller sizes. The key seems to be their unique body plan, which is a mixture of features that evolved piecemeal during the Triassic and earliest Jurassic, culminating in an animal perfectly adapted for thriving at large size.

If sauropods had lacked any one of these features—the long neck, the fast growth rates, the efficient lung, the system of skeleton-lightening and body-cooling air sacs—then they probably would not have been capable of becoming such behemoths. It wouldn’t have been biologically possible.

They became biblically huge and swept around the world; they became dominant in the most magnificent way—and they would remain so for another hundred million years.

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.

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.

tyrannosaur—true giants, undoubted top predators of record size—made their first appearance in western North America about 84 to 80 million years ago.