Dinosaurs' Ever-Changing World

When your parents were young, TVs were small and boxy, phones were clunky and wired to walls, and computers were way too big to carry around. Instagram wasn’t a thing, postcards were, and the word “Amazon” only meant a rainforest and river in South America.

Things changed a lot over only a few decades. So imagine how much things change over a person’s entire lifetime. Or centuries.

Or 174 million years! That’s how long dinosaurs ruled the Earth. For comparison, we humans have been around for about 6 million years. And from when dinosaurs first appeared to when they went extinct, the world and everything in it — including the dinosaurs themselves — changed dramatically.

The really, really olden days

When dinosaurs first emerged on Earth more than 230 million years ago during the middle of what we call the Triassic period, our planet looked nothing like it does today. Instead of the seven separate continents we have today — North America, South America, Africa, Europe, Asia, Australia, and Antarctica — almost all of Earth’s landmass was connected in one fat, C-shaped supercontinent called Pangaea. It wasn’t a place you’d like to visit (even if meat-eating dinosaurs and fierce crocodile-like creatures weren’t roaming around looking for their next meal).

The shape of Pangaea meant that a lot of the supercontinent’s land was really, really far from the ocean. Cool, moist ocean air could not reach those inland areas, so scientists believe they were like hot, dry deserts. The coasts were wetter, but not exactly a paradise. They got hit by powerful monsoons, storms with very heavy rainfall and strong, blustery winds.

Not many types of plants grew on Pangaea. In the areas with more moisture, evergreens — plants usually with needles instead of leaves — grew in many shapes and sizes, from towering trees to little shrubs. Along with ginkgo trees, they even formed forests. Elsewhere, ferns and mosses covered the land.

The extreme conditions — harsh climate and limited plant variety — supported fewer types of animals than at other times in Earth’s history. Early mammals, mainly mouse-sized insect-eaters, lived in areas with more water. But the animals best suited to the harsh habitat were the archosaurs, a group of reptiles that evolved into various types of crocodiles, birds, pterosaurs (flying reptiles), dinosaurs, and many other reptiles that later went extinct.

Of those groups, the true rulers of the Triassic period were the crocodile-like archosaurs. Compared to the crocs, the dinosaurs of the Triassic weren’t as diverse.  And they also were pretty small — at least by dino standards. For example, the speedy meat-eater Coelophysis, which scampered along on two legs, was only about as tall as a Great Dane (but with a much longer tail). The huge, long-necked sauropods and mighty tyrannosaurs didn’t exist yet. The dinosaurs had not begun their reign on Earth.

But that was about to change.

Dinosaurs dominate

The Triassic period ended much like it began: with a mass extinction of many animals.

The climate had changed a lot by the end of the Triassic period. Temperatures had climbed, melting ice had caused sea levels to rise. And ocean waters had become more acidic — toxic to many marine animals. Scientists aren’t sure exactly what caused the dramatic climate change, but volcanoes may have been to blame. In an area now covered by the Atlantic Ocean, volcanoes spewed enough gases into the air that they probably changed the environment.

A lot of animals could no longer survive in those new conditions, and as many as 80 percent of all species went extinct. Among them were most of the Triassic archosaurs. But their death opened a lot of the natural surroundings for other animals, and dinosaurs took advantage of the situation.

Throughout the Jurassic period — which followed the Triassic and lasted roughly from 200 million to 145 million years ago — dinosaurs dominated the land. They evolved into many types, some growing to massive sizes. Towering, long-necked sauropods, such as Diplodocus and Brachiosaurus, munched the leaves of tall plants. Fierce meat-eaters, like Allosaurus, stalked Stegosaurus, an armored dinosaur with plates down its back and spikes on its tail. Little mammals stayed out of their way, scurrying around the forest floor.

Changes in Earth helped dinosaurs flourish during the Jurassic period. Pangaea had started tearing apart during the Triassic, and the process grew faster during the Jurassic — though it still took millions and millions of years. The supercontinent first broke into two continents, Laurasia in the North and Gondwana in the South. Laurasia split to form North America and Eurasia, then Gondwana began to break up into South America and Africa in the West, and Antarctica, Madagascar, India and Australia in the East.

The breakup of Pangaea allowed oceans to flood into the spaces between the new, smaller continents. Cooler, moister ocean area made the climate less extreme. In contrast to the Triassic’s hot and dry climate, the Jurassic was more humid and subtropical — warm and pretty rainy.

The warm, rainy climate was great for plant growth. The types of plants did not change a lot from the Triassic to the Jurassic, but they were much more plentiful. Forests of evergreens, tall palm tree-like plants, ginkgoes, and ferns provided plant-eaters with plenty to eat. And the plant-eaters, in turn, provided food for the meat-eaters.

The height of the Dinosaur Era

Dinosaurs continued to dominate the Cretaceous period, which followed the Jurassic and lasted roughly from 145 million to 66 million years ago. (Together, the Triassic, Jurassic and Cretaceous periods make up the larger Mesozoic era, which often is called the “Dinosaur Era.”)

During the Cretaceous period, dinosaurs thrived, evolved, and reached their greatest sizes. The largest land animals that ever lived — the massive titanosaurs, including Argentinosaurus and Dreadnoughtus — emerged during the late Cretaceous. Horned and frilled dinosaurs, including Triceratops, also made their appearance, as did the heavily armored ankylosaurs. Herds of other plant-eaters, including the bone-headed pachycephalosaurs and duck-billed hadrosaurs, roamed the lush surroundings. Fierce meat-eaters Velociraptor, Spinosaurus and Tyrannosaurus rex feasted on the plentiful plant-eaters.

Though dinosaurs ruled the land, other animal life — including birds, marine animals, insects, reptiles and amphibians — also transformed, with many fish, snakes and lizards evolving to look much like they do today. Different groups of mammals also emerged during the Cretaceous, though they were still smaller than today’s rabbits.

What made all that wildlife possible? A bounty of good eats! Over the stretch of the Cretaceous period, plant life truly blossomed. Flowering plants, which first appeared around the beginning of the Cretaceous, dominated the landscape by the end of the period. Alongside the evergreens, ferns and ginkgoes of earlier periods, Cretaceous habitats included forests of magnolias, poplars, willows, sycamores, figs and flowers.

That doesn’t mean that habitats were the same everywhere. During the Cretaceous, the continents continued to drift farther apart, ending up roughly in their current positions by the end of the period. Though the climate everywhere was warmer and more humid than today, it varied among the scattered continents — and was certainly different from Pangaea’s extreme environment. Forests covered even the polar regions, and seas covered more of the continents than they do today.

When the continents drifted apart, plant and animal life on the different continents began to transform separately. Over tens of millions of years, different types of dinosaurs thrived on different continents. In the northern continents that split from Laurasia — especially today’s North America and Asia — many varieties of duck-billed hadrosaurs and tyrannosaurs, including T. rex, dominated the land. Farther south, across vast ocean waters, the long-necked sauropods and horned meat-eaters, like Carnotaurus, were more common in the continents that split off Gondwana, including South America and Africa.

A diverse era

Scientists discover a new dinosaur roughly every ten days. They already know of 700 to 800 different species and suspect there may have been thousands. But all those dinosaurs didn’t live at the same time or place.

The “Dinosaur Era” was several periods — Triassic, Jurassic and Cretaceous — each with its own distinct climates, oceans and land features. Those differences shaped distinct habitats for animals and plants, allowing different kinds of dinosaurs to evolve and go extinct — even before the asteroid impact that ended the dinosaurs’ reign on Earth.

From when the first dog- and horse-sized dinosaurs of the Triassic appeared to when the giant and ferocious dinosaurs of the late Cretaceous met their end, dinosaurs and their world sure changed.