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Dinosaur is the of certain extinct reptiles.


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dinosaurs.
Dinosaur nests in western Montana.

As for reproduction, considerable evidence is now available. The idea that dinosaurs, like most living reptiles and birds, built nests and laid eggs had been widely debated before the 1920s, when a team of scientists from the American Museum of Natural History made an expedition to Mongolia. Their discovery of Dinosaur eggs in the Gobi proved conclusively that at least one kind of dinosaur, Protoceratops, had been an egg layer and nest builder. These findings were substantiated in 1978 when John R. Horner discovered Dinosaur nests in western Montana. A few other finds, mostly of eggshell fragments from a number of sites, established oviparity as the dinosaurian mode of reproduction.

'Dinosaur' is the common name given to any of certain extinct reptiles, often very large, that thrived worldwide for some 150 million years and that died out at the end of the Mesozoic Era, about 66.4 million years ago. The popular name comes from the Greek words deinos (terrible) and sauros (lizard).

The English anatomist Richard Owen proposed the formal term Dinosauria to designate certain giant extinct animals represented by large fossil bones that had been unearthed at several locations in southern England during the early part of the 19th century. Originally applied to just a handful of incomplete specimens, the category Dinosauria now encompasses more than 550 generic names and at least 1,000 species. Not all of these are valid taxa, however, because of either inadequate specimens, duplication of names, or misidentification of findings as dinosaurian. Nevertheless, certain characteristics of the dinosaurs, such as diversity, longevity, and ubiquitous distribution, are well documented by abundant fossil remains recovered from every continent on Earth.

The extensive list of genera and species is testimony of the many different kinds of animals, with widely divergent lifestyles and adaptations, that are known as dinosaurs. Their remains are found in sedimentary rock strata laid down over a period ranging from roughly 230 to 66.4 million years ago (from the Middle Triassic Epoch to the end of the Cretaceous). The abundance of their fossil bones is substantive proof that Dinosaurs were the dominant form of terrestrial animal life during the Mesozoic Era. It is likely that the known remains represent a very small fraction, probably less than 0.0001 percent, of all the Dinosaurs that once lived. New kinds are added to the roster every year through scientific explorations around the world.

Before Richard Owen introduced the word in 1841, there was no concept of anything like a dinosaur. Quite probably, large fossil bones had been observed long before that time, but there is little record, and no existing specimens, of such findings before 1818. Dragons of Asian and Western legends would seem to have been generated by very early fossil discoveries (which later might have proved to be Dinosaur remains), but there is no historical evidence to that effect.

Early 19th-century discoveries

The earliest published record of fossil remains that still exist for verification as dinosaurian was a note in the 1820 American Journal of Science and Arts by Nathan Smith. The bones had been found in 1818 by Solomon Ellsworth, Jr., while he was digging a well at his homestead just east of the Connecticut River in Windsor, Conn., U.S. At the time, the bones were thought to be human, but much later they were identified as Anchisaurus . Even earlier (1800), large birdlike footprints had been noticed on sandstone slabs farther north, in Massachusetts. Pliny Moody, who discovered these tracks, attributed them to Noah's raven, and Edward Hitchcock of Amherst College, who began collecting them in 1835, considered them to be those of some giant extinct bird. The tracks are now recognized as having been made by several different kinds of dinosaurs, and such tracks are still commonplace in the Connecticut River valley today.

Better known are the finds in southern England during the early 1820s by William Buckland, a clergyman, and Gideon Mantell, a physician, discoverers respectively of Megalosaurus and Iguanodon . In 1824 Buckland published a description of the original specimen of Megalosaurus, which consisted of a lower jawbone with a few teeth. The following year Mantell published his Notice on the Iguanodon, a Newly Discovered Fossil Reptile, from the Sandstone of Tilgate Forest, in Sussex, based on several teeth and some leg bones. Both men collected fossils as an avocation and are credited with the earliest published announcements of what later would be recognized as dinosaurs. In both cases, their finds were too fragmentary to permit a clear image of either original animal. In 1834 a partial skeleton was found near Brighton, Eng., which corresponded with Mantell's fragments from Tilgate Forest. It became known as the Maidstone Iguanodon, named after the village where it was discovered. The Maidstone skeleton provided the first glimpse of what these creatures might have looked like.

Two years before the Maidstone Iguanodon came to light, a different kind of skeleton was found in the Weald of southern England. It was described and named Hylaeosaurus by Mantell in 1832 and later proved to be one of the armoured dinosaurs. Other fossil bones began turning up in continental Europe: fragments described and named as Thecodontosaurus and Palaeosaurus by two English students, Henry Riley and Samuel Stutchbury, and the first of many skeletons named Plateosaurus by the naturalist Hermann von Meyer in 1837. Richard Owen named two other fragmentary specimens: a single large tooth that he called Cladeiodon and an incomplete skeleton composed of very large bones that he named Cetiosaurus . Having carefully studied most of these fossil specimens, Owen recognized that all of these bones represented a group of large reptiles that were unlike any living varieties. In a report to the British Association for the Advancement of Science in 1841, he termed these animals Dinosauria, and the word was first published in the association's Proceedings in 1842.

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Original Source - http://www.crystalinks.com/   Alternative Theory On Dinosaurs  

Paleontology


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