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When did dinosaurs first appear?

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Quick Answer

The first true dinosaurs first appeared about 230 million years ago. The first dinosaur fossils are distinguished from those of their reptile ancestors by their more upright stance, with legs directly beneath the body instead of splayed to the side, as with other reptiles. The earliest dinosaur fossils were found in South America, although a December 2012 fossil discovery in southern Africa casts some doubt on a South American origin.

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Full Answer

The first dinosaurs were a group of species known as theropods. They walked on two legs and varied in size from the 20-pound Eoraptor to the 400-pound Herrerasaurus. The group spread relatively quickly from South America to North America, and then further to Africa and Eurasia. Many famous types of dinosaur, including tyrannosaurs and allosaurs, were later species of theropod.

Dinosaurs with four legs evolved from theropods, but they are not considered theropods themselves. These species, which were mostly herbivores, were split into two groups by their hip structures. Lizard-hipped species included the giant sauropods. Bird-hipped groups included the armored anklyosaurs and the horned ceratopsians. Scientists think that all bird-hipped dinosaurs descend from a species called Eocursor, a species from South Africa, which, in turn, was probably descended from Eoraptor.

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Related Questions

  • Q:

    Where did dinosaurs come from?

    A:

    Dinosaurs come from the evolution of early primitive organisms approximately 230 million years ago and it is unknown why these organisms evolved into dinosaurs. Scientists have been able to trace dinosaurs back 228 million years ago to one of the first species known as the "eoraptor" that was the size of a dog and was carnivorous.

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  • Q:

    How did the Tyrannosaurus rex reproduce?

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    The Tyrannosaurus rex, like other dinosaurs and their surviving modern-day bird relatives, reproduced sexually. The female then laid fertilized eggs from which newborn tyrannosaurs would hatch.

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  • Q:

    Why was the brontosaurus's name changed to the apatosaurus?

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    The gigantic, herbivorous Brontosaurus, which features an iconically long neck and tail, may be one of history's most famous dinosaurs, but its existence as a unique species was debunked in 1903, when someone realized that the skeleton that had been labeled as a Brontosaurus was actually an Apatosaurus. In this sense, the Brontosaurus was not renamed but rather determined to have never existed as a separate species. The same man, a Yale paleontologist named Othniel Charles (O.C.) Marsh, named both the Apatosaurus and the Brontosaurus, with the Apatosaurus discovery predating the Brontosaurus naming by two years.

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  • Q:

    Are there animals alive today that lived beside dinosaurs?

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    There are some animals on earth that can be traced back to the Mesozoic Era when dinosaurs walked the earth; these animals include monotremes such as the duckbill platypus, reptiles such as the crocodilians and sea creatures such as the sea urchin. For the most part, the animals that are alive today have made evolutionary changes from the forms they had when dinosaurs were alive. For example, though the event that caused dinosaurs to die out also killed many other reptile species, several surviving reptile species have direct ancestors from that era, including the crocodilians, which are smaller than their Mesozoic ancestors.

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