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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
..... Click the link for more information. . 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 Owen, 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 are 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 many 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.
..... Click the link for more information. , 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
..... Click the link for more information. , 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.
..... Click the link for more information. , 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.
..... Click the link for more information. [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.
..... Click the link for more information. ). 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.
..... Click the link for more information. ; 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
..... Click the link for more information. 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.
..... Click the link for more information. ; 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,
..... Click the link for more information. . 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.
..... Click the link for more information. for more information.) No theory perfectly describes why 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.
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.
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.