Q:

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:

    Why are dinosaurs extinct?

    A:

    There are a few well-researched theories about why dinosaurs are extinct; one of the most prominent theories hypothesizes that a massive asteroid impact killed off the dinosaurs. Another states that heavy volcanic eruptions across the Earth may have been responsible.

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  • Q:

    Is it possible to clone dinosaurs?

    A:

    It is very unlikely that a dinosaur can be cloned. The essential element, a complete dinosaur genome, is extremely unlikely to exist after 65 million years. Genetic material is made out of deoxyribonucleic acid (DNA), and it breaks down over time.

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  • Q:

    Were there any dinosaurs that swam?

    A:

    True dinosaurs were not swimmers. There were a number of very large aquatic reptiles that lived during the age of the dinosaur, but they were not technically dinosaurs. These creatures belonged to one of several other groups, such as ichthyosaurs, plesiosaurs and mosasaurs, which were types of marine reptiles.

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  • Q:

    Are there animals alive today that lived beside dinosaurs?

    A:

    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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