Dinosaurs lived on earth for over 140 million years. They lived during the<br >TRIASSIC, JURASSIC and CRETACEOUS periods. Suddenly, about 65<br >million years ago, they vanished.<br > The first animals were invertebrates (animals without backbonesl, which<br >lived in the sea. About 400 million years ago, invervebrates evolved into fishes<br > and then amphibians. Amphibians are the simplest forms of vertebrates (ani<br > reals with backbones). They are cold-blooded animals that live in the sea in<br > their early years and then live on land when they mature. Reptiles came next<br > and they were the ancesvors of all dinosaurs, birds and mammals. (See Geologi-<br > cal Time Chart.) Dinosaurs are the direct descendants of the THECODONTS,<br > heavy, four-legged, flesh-eating reptiles. Later, some Thecodonts became the<br > first upright-mowng animals, using their long, strong tails for balance.<br > ~ saurs evolved from the Thecodonts. They are<br > Many different types of.dino . ,. j ~_Abird.hinned. The lizard-hipped<br > divided into two basic kinds: lizarct-nlppeu m"~ r~<br > group includes all the meat-eaters as<br > well as the giant-sized plant-eaters.<br > The horned, armored, plated and<br > bird-footed (such as Iguanodon) dino-<br > saurs belong to the bird-hipped group.<br > {See Basic Dinosaur Classification--<br > p. 15.) So far, about 340 genera<br > (closely related groups) of dinosaurs<br > have been discovered. They range<br > from the little, two-pound, meat-<br > eating SALTOPUS to the 150-ton,<br > plant-eating ,,ULTRASAURUS." L<br > The first dinosaur fossils were ~ ~1<br > found in England in the early 1800s. Ww<br > Since then they have been found on ~ ~l%a k g<br > east Hl~"<br >
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