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| This chart is the Dinosaur Family Tree from the 1950s. New Study Restructures the Dinosaur Family Tree |
Among the dinosaurs were many different-looking animals, and some were not very closely related to one another. For example, the dinosaur Brontosaurus was no more closely related to the dinosaur Stegosaurus than a cow is to a horse. Not all the dinosaurs were giants. The first dinosaurs were very small, some of them no larger than chickens.
The earliest known dinosaur in our country was about eight feet long. He is called Coelophysis (see-lo-FYE-sis) and he lived during the last part of the Triassic period. His fossil skeletons have been found in northern New Mexico. Most of his eight-foot length was made up by a long, slender tail. He was very lightly built and perhaps weighed no more than fifty pounds. Because of his light build he was probably able to run very fast. His small front legs were equipped with claws that were useful in grasping and tearing food. His teeth were sharp and he probably preyed on small reptiles. He walked on his hind legs.
It is a very important to remember that the earliest dinosaurs walked on their hind legs. As the dinosaurs continued to develop, some of them grew larger and heavier and came down on their front legs to support themselves better. Because of this, most of these dinosaurs had an arched back and shorter front legs than hind legs. But there was a dinosaur called Brachiosaurus that is an exception.
Paleontologists, the scientists who study prehistoric animals, have divided the dinosaur family into two large groups. One group is named the reptile hips - and the other the bird hips - because their hip bones resemble in arrangement the hip bones of either reptiles or birds. The reptile-hipped dinosaurs included both plant-eaters and meat-eaters, but the bird hipped dinosaurs were all plant-eaters.
Some of the reptile-hipped dinosaurs walked on their large muscular hind legs and used their front legs only for grasping. Many of these dinosaurs were very large and weighed eight or more tons, and some were very small. We know that nearly all of them were meat-eaters because they had long, sharp, pointed teeth. The gigantic four-legged forms in the reptile-hipped group, such as Brontosaurus and Brachiosaurus, had very long tails, long necks, and small heads. They had spoon-shaped or peg-like teeth and were plant-eaters.
The armored dinosaurs or the plated dinosaurs and the horned dinosaurs, and the duck-billed dinosaurs all belong to the group of bird-hipped dinosaurs. All the bird-hipped dinosaurs were plant-eaters. Some of them walked on four legs, others only on their hind legs. Most of these dinosaurs developed spectacular structures for defense against their enemies, the meat-eating dinosaurs. Some had long, sharp horns. Others had double rows of fan-shaped plates up their backs and spikes on their tails. Others had bony plates over the body, spikes along the sides of the body, and a long club-like tail. And still others had duck-like bills and bony crests or long tubes extending back from the top of their heads.
In what parts of the world did the dinosaurs live? Fossil skeletons of dinosaurs have been found all over the world and on nearly every continent. The largest number of dinosaur skeletons and some of the most interesting kinds have been found right in our own country. The first dinosaur skeleton found in the United States was at Haddonfield, New Jersey, but most of the skeletons have been found in Montana, Wyoming, Colorado, Utah, and New Mexico. At Dinosaur National Monument near Jensen, Utah, you can see parts of dinosaur skeletons sticking out of the rocks. At the time that the dinosaurs were alive, our planet looked much different than it does today.
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