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[Gr.,=terrible lizard], Extinct land reptile of the Mesozoic era. The dinosaurs, which were mostly egg-laying animals, ranged in length from 2 1 2 ft (91 cm) to about 90 ft (27 m). 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 resembled that of still-extant reptiles. In the ornithischian (bird-hipped) dinosaurs the pubic bone of the pelvis had forward and backward extensions and so superficially resembled that of a bird. The jaws and teeth of the two groups also differed. The saurischian order, which included both herbivores and carnivores, had teeth around the entire jaw or confined to the front of the mouth. Ornithischians had 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. Fossil remains of dinosaurs have been found in rock strata of every continent, indicating that they differed widely in structure, habitat, and diet. Some, it is argued, may have been warm blooded. Their brain sizes also varied, with some predators having brain-to-body ratios equivalent to those of some modern birds and animals. Some birds are believed to be the living descendants of certain ornithischians. Evidence shows that most dinosaurs traveled in herds, some migrating great distances. Many species built nests. Many explanations have been offered for the worldwide extinction of the dinosaurs after 140 million years of existence. During the Upper Cretaceous, for example, crustal disturbances may have resulted in the draining of swamps, destroying the natural habitat of many dinosaurs. Other theories point to the formation of mountains, which caused colder climates in which reptiles cannot thrive. Other factors may have included the destruction of herbivorous forms by carnivorous types and the inability of the large, clumsy dinosaurs to compete with the small, fleet mammals, which were gradually becoming more numerous. Evidence of a massive meteor impact off the Yucatan coast 60 million years ago has led to a recent theory that global climate changes accounted for their extinction. Of the saurischian dinosaurs, some were carnivorous bipeds, such as Tyrannosaurus; some, herbivorous quadrupeds, such as Brontosaurus and Diplodocus. Among the ornithischians, Iguanodon was duck-billed, Stegosaurus was armored, and Triceratops was horned. See D. Norman, The Illustrated Encyclopedia of Dinosaurs (1985); J. N. Wilford, The Riddle of the Dinosaur (1985); R. Bakker, The Dinosaur Heresies (1986).
See What The World Was Like Millions Of Years Ago
 Mesozoic era
(Gr.,=middle life), A major division of geologic time from 66 to 205 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 topography of North America. The Appalachian geosyncline, or downward thrust of the earth's crust, was replaced by the Appalachian Mts., and the eastern part of the continent was elevated during most of the era. The Appalachians were subjected to erosion, the products of which were deposited along the Atlantic coast, which had become a lowland region, or in the ocean beyond. Aside from the Appalachians, the other dry (consistently) areas of the continent were the Canadian Shield, the Antilles areas, and a mountain range elevated in part of the Cordilleran geosyncline. The Mesozoic tectonic activity included numerous subduction zones, such as those along the Pacific margin of the supercontinent Pangaea. Later, Pangaea began to split into the supercontinents of Gondwanaland and Laurasia, and N Africa began to rift apart. By the late Mesozoic, tectonic activity increased dramatically: the new Indian Ocean began to open, the Atlantic Ocean began to open along an extensive rift zone separating the Americas from Europe and Africa. The life of the Mesozoic was dominated by the reptiles that evolved into the large land-dwelling dinosaurs of the Jurassic and Cretaceous periods. Flying reptiles and birds first appeared during the Mesozoic. Mammals probably evolved from some common ancestor of the reptiles early in the Triassic Period, but were subordinate to the reptiles until the end of the era, when the dominance of reptiles was ended by the extinction of the dinosaurs. Conifers dominated the plant life, with modern pines and sequoias first appearing. Flowering plants, deciduous trees, and grasses also appeared during this era.
Tyrannosaurus
[Gr.,=tyrant lizard], A genus of a biped carnivorous dinosaur, about 50 ft (15 m) in length and about 20 ft (6 m) tall, weighing 10 tons, having an elongated skull and large, sharp, daggerlike teeth in jaws that could open to a 4-ft (122-cm) gape. The short forelimbs had three fingers armed, like the three digits of the powerful hind limbs, with sharp, recurved claws; on the foot was a spurred toe not reaching to the ground. The largest and probably the most ferocious terrestrial carnivore that ever lived, the Tyrannosaurus is believed to have existed only for a short time in the late Cretaceous period and to have dominated the North American continent at that time; parts of a few skeletons have been found in Montana and South Dakota. Only one species (Tyrannosaurus rex) is known. The Tyrannosaurus is classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Saurischia.
Brontosaurus
[Gr.,=thunder lizard], A popular synonym for the genus officially known as Apatosaurus [Gr.,=deceptive lizard], a quadruped herbivorous dinosaur, probably over 70 ft (21 m) long and weighing more than 30 tons. It had a long, whiplike tail, stout legs, and was primarily a land-dwelling animal. The eyes and nostrils of these amphibious dinosaurs were located toward the top of the skull, permitting them to see and breathe with only the top of the head above water. Brontosaurus bones and those of other sauropods have long been excavated in the Morrison formation of the late Jurassic and early Cretaceous strata in Colorado, Wyoming, and other Western states. The brontosaurus is classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Saurischia. See S. J. Gould, Bully for Brontosaurus (1991). Diplodocus
[Gr.,=double beam (or rafter)], A quadruped vegetarian dinosaur found in the Jurassic strata of the United States. It had a small head and a long tail and was probably an amphibious inhabitant of the swamp. Some of these animals reached a length of more than 80 ft (24 m), but were more slender and lighter in weight than the related brontosaur (see Brontosaurus). The Diplodocus is classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Saurischia.
 Iguanodon
A biped vegetarian duck-billed dinosaur, characterized by teeth similar to those of the iguana, a powerful tail, and a horny beak. Complete skeletons of the 30-ft-long (9-m) reptile have been found in Belgium in rocks of the Cretaceous period. The Iguanodon is classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Ornithischia. Stegosaurus
[Gr.,=roof lizard], A quadruped vegetarian dinosaur of the Jurassic period. About 20 ft (6 m) long and weighing about 10 tons, it had short forelegs, two rows of upright bony plates on the back, and 4 long bony spikes on the tail. The brain weighed about 2 1 2 oz (71 grams). Complete skeletons were found in the Jurassic beds of Colorado and Wyoming. The Stegosaurus is classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Ornithischia.
Triceratops
A fossil herbivorous quadruped dinosaur of the Cretaceous period of geologic time. Characteristically it had three horns, one on the nose and one over each eye, and a bony shield projecting backward from the skull to serve as a protection to the neck and fore part of the body. The head was large (about 8 ft/2.4 m long), the body (about 20 ft/6 m long) was bulky and barrel shaped, and the limbs were massive and of equal length. Bones of Protoceratops, a related hornless form, and eggs probably belonging to it were found in Mongolia. The Triceratops is classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Ornithischia.
Zoom Dinosaurs
http://www.EnchantedLearning.com/subjects/dinosaurs/
Find out All About Dinosaurs at this site and try some of the Dino Fun and
Games, like:Scrambled Dinosaurs
http://www.EnchantedLearning.com/Slidedinosaurs/Slidedino2.html
Create your own crazy dinosaur or discover a new one! Online Quiz
http://www.EnchantedLearning.com/subjects/dinosaurs/activities/radiobuttonquiz/
Diplodocus - Build Your Own Dinosaur - As you answer the right questions, a
dinosaur picture appears
http://www.iconos.com/toolsbone.html
Find the Dinosaur Skull and try to answer the dinosaur riddles in the What's
in a Name game from the Carnegie Museum of Natural History's Dino Science
page - In this Shockwave game you have to figure out where the dinosaur
bones should go.
http://www.clpgh.org/cmnh/discovery/dinoscience/index.html
Dinosaur Games: Memory Match - Find the matching dinosaur pictures.
http://www.teleport.com/~tosoft/match.htm
Common Questions about Dinosaurs - How long did dinosaur live? How heavy are
their bones? Are they really extinct?
http://www.clpgh.org/cmnh/discovery/dinofaq.html
Zoom Dinosaurs Quiz
http://www.EnchantedLearning.com/subjects/dinosaurs/quiz/q1.shtml
Ready to test your knowledge of dinosaurs? Dino Don also has a Dinosaur Quiz
http://www.dinodon.com/dinosaurs/quiz.html
Dino Russ's Collection of Dinosaur Pictures - See photographs of dinosaur
skeletons.
http://www.isgs.uiuc.edu/dinos/GIFs_path.html
Dinosaur Safari - The Museum of Unnatural History unravels some of the
mysteries of dinosaurs.
http://unmuseum.mus.pa.us/dinosaf.htm
Dinosaur Eggs - Read a National Geographic article about the discovery of
dinosaur eggs. What did baby dinosaurs look like?
http://www.nationalgeographic.com/features/96/dinoeggs/intro.html
The Dinosauria - The Museum of Paleontology at the University of Berkeley
dispels some myths and shares many facts about dinosaurs.
http://www.ucmp.berkeley.edu/diapsids/dinosaur.html
The Dinosauria. What do we know about dinosaurs? How did they live? How did
they die? How do they live on today? Includes a section on myths and
contains links to numerous other dino-sites.
http://www.ucmp.berkeley.edu/diapsids/dinosaur.html
The Dinosaur Hall of the National Museum of Natural History. Photographs
from Smithsonian Exhibits: The Dinosaur Hall, National Museum of Natural
History.
http://photo2.si.edu/dino/dino.html
World's First Dinosaur Skeleton: Hadrosaurus Foulkii. A site about the first
dinosaur fossil found in the United States. Foulke had discovered the first
nearly complete skeleton of a dinosaur, an event that would rock the
scientific world and forever change our view of natural history.
http://www.levins.com/dinosaur.html
 
    
   
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