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The word dinosaur is a Greek word for "terrible lizard"zoic Era. The term was proposed as a formal zoologic name in 1842 by the British anatomist Sir Richard Owen, in reference to large fossil bones excavated in southern England. The animals are classified in two formal categories, the orders Saurischia and Ornithischia, within the reptile subclass Archosauria.
HISTORY
Thousands of dinosaur remains have been found all across the world. The earliest discoveries were for many years attributed to two Englishmen. The first, Gideon Mantell, a doctor, made his find in Sussex, England, in 1822 and called it Iguanodon ("iguana tooth"). The second, the Rev. Willam Buckland, made his find near Oxford, England, and called it Megalosaurus ("great lizard"). In fact, fossil remains had already been discovered in 1818 at Windsor, Conn., by Solomon Ellsworth, Jr. The remains, reported as human by Nathan Smith in the 1820 issue of the American Journal of Sciences and Arts were only recently recognized as pertaining to the Late Triassic/Early Jurassic prosauropod Anchisaurus.
CLASSIFICATIONS & LIFE
Dinosaurs varied greatly in form and size and had adapted for diverse habitats and lifestyles. Their weight ranged from 2 to 3 kg, in the breed of Compsognathus. They weighed to 73 metric tons in the breed of Brachiosaurus. Most known dinosaurs were gigantic, weighing more than 500 kg, and very few weighed less than 45 kg. Supprisngly, most dinosaurs were herbivores, but saurischians such as the theropods were carnivorous. Most dinosaurs were also four-legged. However some were obligatory bipeds, and were unable to adopt to a four-legged posture; a classic example of one may be treachourous trinousaurs-rex. Others were facultative bipeds, meaning they made use of all four legs, but were able to walk on their hind legs when necessary.
Dinosaurs have always been classified as reptiles, because they all have similair features, found in today's living reptiles and not in mammals or amphibians. For that reason they traditionally have been assumed to have been like reptiles in physiology, which is that they were cold blooded, or dependent on external heat sources. In recent years, however, different lines of evidence have been interpreted as indicating that dinosaurs may have been warm-blooded. This was concluded with rates of metabolism, which was comparable to those of mammals and birds. Such evidence includes their upright posture, carriage, mammallike microscopic structure of bones, skeletal features suggestive of high activity, specialized food-processing dentitions, and the low ratios of dinosaurian predators to prey animals, suggesting large food requirements. The evidence is not conclusive, and all the facts can be explained. The possibility remains that some dinosaurs may have been endothermic, which means they were able to maintain body tempreture and heat production by the means of internal metabolic processes.
Evidence indicates that dinosaurs, like most modern reptiles, reproduced by laying eggs. Fossil eggs have been discovered in Mongolia and France, and fragments presumed to be of dinosaur eggs have also been found in Brazil, Portugal, Tanzania, and the U.S. states Colorado, Montana, and Utah. Fossils of unhatched dinosaur eggs have been discovered in Montana and Utah, in Alberta, and in the Gobi Desert. A few scientists suggest that some dinosaurs, such as the sauropods, may have given birth to live young, but no conclusive evidence has been found.
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