The Age of Dinosaurs began about 250 million years ago. In the beginning they were quite small but over time they evolved into the varied and fascinating creatures that captivate our imaginations today. What we know about dinosaurs is evolving, too! We've learned that some dinosaurs were good parents, that dinosaurs could grow new teeth when old ones fell out, and that most dinosaurs walked on two legs. We've even discovered that birds are modern relatives of dinosaurs!
About the Author
Read an Excerpt
What Was the Age of the Dinosaurs?
In 1822, a young country doctor named Gideon Mantell was living in Sussex, England. He delivered babies and treated people with serious diseases.
But Mantell had another passion as well. Ever since childhood, he had loved to collect fossils—the ancient remains of dead plants and animals. Whenever he could, the busy doctor spent time digging near the chalky cliffs of England’s coastline. At first what he dug up were small pieces of fossil bones. But as time went on, he began to find some big bones—really big ones. The bones were too big to belong to any known animal. Even elephant bones would have been smaller.
Then one day, Mantell’s wife, Mary, found a few enormous fossil teeth. She brought them to her husband.
What were they? What kind of animal could possibly have teeth as big as this?
Mantell wasn’t sure what to think. He talked to other scientists. No one could agree about what they were. A man named William Buckland had once been given some huge bones. He studied them for six years and finally decided they belonged to a giant lizard no one had ever seen before. Buckland called it Megalosaurus (say: MEG-uh-lo-SORE-us), which means “big lizard.”
Mantell asked Buckland about the huge teeth he had found. But Buckland didn’t think they had come from a creature similar to his Megalosaurus. He said they came from a fish!
After that, Mantell went to a museum and looked at other fossils and animal skeletons on display. The teeth he had found looked exactly like iguana teeth—only many times larger. If they came from an iguana, it would have to have been at least sixty feet long! That’s as long as a house!
Suddenly Mantell realized something exciting. Like Buckland, he had discovered a new kind of animal no one knew about. He decided to call it Iguanodon (ig-WAN-uh-don).
Neither Mantell nor Buckland understood that they had stumbled onto a completely unknown group of animals. The word dinosaur hadn’t been invented yet—and wouldn’t be for another twenty years. But that’s what Megalosaurus and Iguanodon were. In the early nineteenth century, no one yet realized that in prehistoric times, gigantic animals had roamed the earth. But soon, more fossils were found, and slowly scientists began to put together the pieces of a long-lost world—the Age of the Dinosaurs.
Chapter 1: The Prehistoric World
Two hundred thirty million years ago, the Age of the Dinosaurs began. The first baby dinosaurs poked their heads out of their eggshells and looked around for something to eat.
The earth was a very different place then. North America didn’t exist. Neither did Africa or Europe. All seven continents we know today were clumped together into one huge landmass that we call Pangaea (pan-JEE-uh).
Pangaea was surrounded on all sides by water. The center of the huge continent was a hot desert, where not much could survive. A giant ocean covered the rest of the earth. Near the coastlines, the ocean cooled the air. Cool air and water made it possible for fabulous life-forms to develop. Ferns grew along the coast. Moss covered the rocks. There were forests of pine trees and palm trees. Spiders and beetles crawled about.
The ocean was full of life. There were huge swimming reptiles—animals like lizards and turtles, only bigger. Some, called ichthyosaurs (ICK-thee-oh-sores), looked much more like dolphins or fish. They were predators that hunted fish. Others, called plesiosaurs (PLEE-see-oh-sores), were more like gigantic shell-less turtles with incredibly long necks. They may have eaten baby ichthyosaurs for lunch.
Reptiles also dominated the land at that time. There were none of the animals we know today—no dogs, cats, giraffes, monkeys, or apes. There weren’t even any birds—and definitely no people! It was mostly a reptile’s world, although the ancient reptiles were not the same reptiles we know today.
This was the beginning of a time period called the Mesozoic era. It began 250 million years ago—or 250 “mya,” as scientists say. It lasted until the dinosaurs died out, around 65 mya.
The Mesozoic era is divided up into three parts—Triassic, Jurassic, and Cretaceous. The very first dinosaurs appeared on earth during the last part of the Triassic, about 230 mya. Dinosaurs existed on earth for about 165 million years.
When exactly did the first dinosaur appear? It’s hard to say for sure, because dinosaurs evolved from other reptiles over millions of years. But the earliest dinosaur was probably Eoraptor (EE-oh-RAP-tor)—a small animal weighing between eight and twenty-two pounds. With jagged teeth, long legs, and long claws, it was a small, quick, deadly predator. It lived in the forest, where it chased and captured smaller creatures. It probably ate plants, too.
As millions of years went by, different kinds of dinosaurs came into being. How did that happen? The answer lies in evolution.
Evolution is the name for changes that occur in living things over time. Charles Darwin was a scientist in the nineteenth century who studied nature. He wrote a famous book about the idea of evolution. Darwin said that, in each species, some would survive longer than others. It was not just a matter of luck. Those that survived were the best suited to thrive in the world. They lived long enough to have babies that would be born with the same strong traits. Animals of the same species without those traits didn’t live as long. In time, they died out.
Darwin explained that over thousands and millions of years, all kinds of species developed—including human beings, who evolved from ape-like creatures.