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dinosaur

(dī`nəsôr) [Gr., = terrible lizard], extinct land reptile of the Mesozoic eraMesozoic era
[Gr.,=middle life], major division of geologic time (see Geologic Timescale, table) from 65 to 225 million years ago. Great crustal disturbances that marked the close of the Paleozoic and the beginning of the Mesozoic eras brought about drastic changes in the
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. The dinosaurs, which were egg-laying animals, ranged in length from 2 1-2 ft (91 cm) to about 127 ft (39 m). Recognized discoveries of fossilized dinosaur bones date only to the 1820s; Sir Richard OwenOwen, Sir Richard,
1804–92, English zoologist and comparative anatomist. He studied medicine in Edinburgh and in 1827 joined the staff of the Hunterian museum of the Royal College of Surgeons, where he was first Hunterian professor of comparative anatomy and physiology
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, a Victorian anatomist, coined the term dinosaur.

Dinosaur Traits and Classification

Fossil remains of dinosaurs have been found in rock strata of every continent, indicating that they differed widely in structure, habitat, and diet. Their brain sizes varied, with some predators having brain-to-body ratios equivalent to those of some modern birds and animals. Many species built nests. Many theories regarding dinosaurs and their behavior have been hotly debated by the experts. These include the debate over the grouping of birds with dinosaurs, the question of whether nonavian dinosaurs were cold-blooded (ectothermic) or warm-blooded (endothermic), the question of whether dinosaurs protected and nurtured their young in the nest after hatching or whether the young were mobile and self-sufficient at birth, and the reason for the disappearance of nonavian dinosaurs.

No complete fossil dinosaur has ever been discovered. Inferences must be made from fragments or pieces that have been compressed and distorted. Information about the diet has been gleaned from stomach contents and coprolites (fossilized dinosaur feces) and by comparing the teeth to those of living animals, for example, relating the large grinding teeth of hadrosaurs to those of living herbivores. Fossilized dinosaur footprints, such as the trackways found at Davenport Ranch in Texas, have been interpreted as evidence that some dinosaurs traveled in herds; bonebeds containing large numbers of certain dinosaurs, as have been found in Alberta, Canada, have also been seen as evidence of this. What is known about dinosaurs is that, far from being evolutionary failures, they dominated their habitats for much of their 160 million years of existence (the human species Homo sapiens has existed for approximately 150,000–200,000 years).

Although all dinosaurs were originally classified in a single order, it was later discovered that the group contained two distinct types distinguished by structural differences. The pelvis in the saurischian (lizard-hipped) dinosaurs resembles that of still-extant reptiles, but in the ornithischian (bird-hipped) dinosaurs the pubic bone of the pelvis has forward and backward extensions that resemble those found in birds. It was later determined, however, that the backward-tilting hips of ornithischian dinosaurs and birds were the result of convergent evolution and not inheritance. Many other shared characteristics have been noted between birds and saurischians, and it is now believed by most paleontologists that modern birds are in fact extant dinosaurs, descended from the theropods of the saurischian order.

The jaws and teeth of the two dinosaur orders also differ. The saurischian order, which includes both herbivores and carnivores, has teeth around the entire jaw or confined to the front of the mouth. Ornithischians have "cheek teeth" along the sides of the jaw, but never in the front; the bones at the front of the mouth sometimes developed into the horny beaks typical of modern turtles. All known ornithischians were herbivores.

Dinosaurs are further classified into some common groupings. In the saurischian dinosaurs, some were theropods [Gr., = beast feet], a group sharing hind feet with only three functional toes (e.g., the carnivorous bipeds TyrannosaurusTyrannosaurus
[Gr.,=tyrant lizard], member of a family, Tyrannosauridae, of bipedal carnivorous saurischian dinosaurs characterized by having strong hind limbs, a muscular tail, and short forelimbs. Tyrannosaurids are theropods, having three toes on the hind feet.
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, VelociraptorVelociraptor
[Gr.,=swift robber], swift bipedal carnivorous dinosaur of the late Cretaceous period. It was relatively small, being approximately 6 ft (1.8 m) long. It was similar to Deinonychus
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, DeinonychusDeinonychus
[Gr.,=terrible claw], swift bipedal carnivorous dinosaur of the early Cretaceous period, approximately 119–93 million years ago. Fossil specimens have been discovered in Montana and Wyoming. Adults were around 10 ft (2.5 m) from head to tail and 1 ft (3 m) high.
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, and possibly the living birds); others were sauropods [Gr., = lizard feet] with small heads and long necks (e.g., the herbivorous quadrupeds ApatosaurusApatosaurus
, [Gr.,=deceptive lizard], quadruped saurischian dinosaur, estimated to be from 70 to 90 ft (21 to 27 m) in length and to weigh up to 30 tons (27 metric tons). The similar dinosaur formerly called Brontosaurus [Gr.
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 [including those specimens formerly called Brontosaurus] and DiplodocusDiplodocus
[Gr., = double beam (or rafter)], immense quadruped herbivorous dinosaur found in the late Jurassic strata of the Colorado, Utah, and Wyoming. It had a long whiplash tail and a small horselike head with nostrils placed high, just below and between the eyes.
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). Among the ornithischians, there were ornithopods (bird-footed dinosaurs), such as IguanodonIguanodon
[Gr., = iguana tooth], herbivorous ornithiscian dinosaur, characterized by teeth similar to those of the iguana, a horny beak, spikelike thumbs, and a powerful tail. It may have been capable of walking on either two or four feet.
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; thyreophorans (armored dinosaurs), such as StegosaurusStegosaurus
[Gr.,=roof lizard], quadriped ornithischian dinosaur of the late Jurassic period. About 29 ft 6 in (9 m) long, it had short forelegs, four long bony spikes on a flexible tail, and two rows of upright triangular bony plates running along the back, which gave it a
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 and AnkylosaurusAnkylosaurus
, [Gr.,=crooked lizard], genus of heavily armored, herbivorous quadripedal dinosaurs, the best known of which is the species A. magniventris, the largest and heaviest of the ankylosaurs.
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; and ceratopsians (horned dinosaurs), such as TriceratopsTriceratops
[Gr., = three-horn face], genus of ornithischian quadruped dinosaurs of the late Cretaceous period. Because of some variations in sample fossils, it was thought at one time that there were as many as 16 different species, but only one species,
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. The total number of dinosaur genera that existed is unknown; new species are discovered every year, but some species, on further examination, are found to be redundant with earlier finds. One estimate of the possible number of distinct genera exceeds 1,800.

Similarities of dinosaurs found on what are now different continents have given scientists clues to the breakup of the supercontinent Pangaea, which began about 170 million years ago. For example, the discovery of a 130-million-year-old African dinosaur similar to the North American Allosaurus suggests that the African plate was connected to the northern continents (Laurasia) longer than had been believed previously.

The Extinction of the Dinosaurs

Many explanations have been offered for the worldwide extinction of the dinosaurs at the end of the Mesozoic after 160 million years of existence. The most popular theory is that one or more asteroids or comets hit the earth, lifting massive amounts of debris and sulfur in the air and blocking the sunlight from reaching the earth's surface. The 1991 discovery of the Chicxulub crater on the Yucatán peninsula in Mexico lent support to this idea. The second currently popular theory is that the extinctions followed the huge volcanic eruptions that created the lava flows of the Deccan Traps in what is now India. (See mass extinctionmass extinction,
the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events.
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 for more information.) No theory perfectly describes why nonavian dinosaurs, pterosaurs, and many marine organisms were affected by the extinction, when many mammals and other animals (e.g., turtles and crocodiles) survived. The extinction of the dinosaurs led to the geologically rapid evolution of mammals from a group of relatively small creatures to a diverse one that included many megafauna.

Bibliography

See R. Bakker, The Dinosaur Heresies (1986); D. Lambert, The Ultimate Dinosaur Book (1993); D. Lessem and D. Glut, The Dinosaur Encyclopedia (1993); P. Taquet, Dinosaur Impressions (1994, tr. 1998); M. A. Norell et al., Discovering Dinosaurs in the American Museum of Natural History (1995); J. R. Horner, Dinosaur Lives (1997); D. B. Weishampel et al., ed., The Dinosauria (2d ed. 2004); D. Nash, The Great Dinosaur Discoveries (2009); S. D. Sampson, Dinosaur Odyssey (2009).

What does it mean when you dream about dinosaurs?

In a dream, any creature can symbolize the animal self. As a long-extinct creature, a dinosaur can represent the sense that, at some level, we are the products of a very ancient process.

dinosaur

[′dī·nə‚sȯr]
(paleontology)
The name, meaning terrible lizard, applied to the fossil bones of certain large, ancient bipedal and quadripedal reptiles placed in the orders Saurischia and Ornithischia.

dinosaur

dinosaurs died out, unable to adapt to environmental change. [Ecology: Hammond, 290]

dinosaur

any extinct terrestrial reptile of the orders Saurischia and Ornithischia, many of which were of gigantic size and abundant in the Mesozoic era

dinosaur

(1)
Any hardware requiring raised flooring and special power. Used especially of old minicomputers and mainframes, in contrast with newer microprocessor-based machines.

In a famous quote from the 1988 Unix EXPO, Bill Joy compared the liquid-cooled mainframe in the massive IBM display with a grazing dinosaur "with a truck outside pumping its bodily fluids through it". IBM was not amused.

Compare big iron; see also dinosaurs mating.

dinosaur

(2)
[IBM] A very conservative user; a zipperhead.

Dinosaurs

(dreams)
Dinosaurs are always fascinating, sometimes lovable, mostly dangerous, and they are alive only in our imaginations. Consider all of the details of the dream and try to tie these ideas to some aspect of your life. The dinosaur, whether you have given it a positive or negative connotation, represents something from your past or an aspect of your personality that you have altered over time. Dinosaurs may represent old issues that have not been properly addressed and that continue to have the power to affect your life in the present.
References in periodicals archive ?
The only possible dinosaurian ichnites from the Red Head Member are functionally tridactyl or even didactyl tracks with an unusually elongate digit IV and an apparent trenchant claw on digit II assigned to the ichnogenus Evazoum (Lockley and Lucas 2013; Fig.
The rocks of Lameta Formation have been worked out in detail by earlier workers in the context of their depositional environments and the occurrence of dinosaurian remains within them Ample literature is also available on the various aspects related to the Deccan volcanic activity, however the nature of contact between the Lameta Formation and Deccan Traps has not been clearly documented and needs an in depth investigation, which can certainly provide answers to the topical issues of Cretaceous--Tertiary transition and mass extinctions.
What is remarkable is that this tendency to have more species at a bigger size seemed to evolve quite early on in dinosaurian evolution around the Late Triassic period, 225 million years ago, raising questions about why they got to be so big," said Dr David Hone from Queen Mary's School of Biological and Chemical Sciences.
Because so many other lines of evidence support the dinosaur/bird relationship, finding these proteins helps make the case that these structures are dinosaurian in origin.
The little work done on the eggs since Kitching's find seemed to cast doubt on their dinosaurian origin.
Visitors to Dawn of the Dinosaurs will meet one of the first dinosaurs, Coelophysis, a voracious predator who led the way to dinosaurian dominance of the planet and New Mexico's official state fossil.
But there are certain poetic infelicities which, touchstones, down-to-earth verisimilitudes, icons even, of modernity though they may be, I am too dinosaurian appreciatively to accept - i.
These extremely primitive birds date from about 70 million years ago, in the Cretaceous period, and retain many characteristics of their dinosaurian ancestors, researchers say.
They independently reached about the largest size possible for a dinosaurian carnivore.