The word dinosaur is a very broad classification (like the word mammal) for many animals which may be only distantly related (for example, the elephant and the mouse are both mammals). They may be classified according to their anatomy, using their hip bones, yielding 2 groups: (1) Saurischia (lizard-hipped), and (2) Ornithischia (bird-hipped).

    Animals, including dinosaurs, may also be classified by their mode of feeding. An herbivore eats plants, a carnivore eats meat (usually plant eaters), and an omnivore eats both plants and meat.

Theropods or Carnosaurs: large, heavy, powerfully built meat eaters, with huge claws and teeth. (Examples: Allosaurus, Tyrannosaurus)

Dromaeosaurs: small, lightly built, flatfooted, agile, small sharp teeth, meat eaters with a relatively large head and brain, intelligent hunters (Example: Deinonychus, Velociraptor)

Oviraptors ("Bird stealers"): lightly built, bird-like dinosaurs resembling the original ancestor of dinosaurs (thecodonts); preyed on small animals and eggs. (Examples: Oviraptor, Coelophysis, Stenychosaurus)

Sauropods: large bodied, long necked, long tailed, plant eaters with pillar like legs. (Examples: Brontosaurus, Diplodocus, Brachiosaurus)

Stegosaurs: armored plant eating dinosaurs with bony plates along their backs, long sharp tail spikes, very small head, and short front legs (Example: Stegosaurus)

Ankylosaurs: short, squat, armored dinosaurs with a "full armor suit," often with spikes and tail club (Example: Ankylosaurus)

Hadrosaurs ("Duck-bills"): medium sized (up to 30 feet long), semi-aquatic dinosaurs, having a large, flat, duck-like beak with thousands of plant grinding teeth, webbed feet and fingers. (Example: Saurolophus, Anatosaurus, Lambeosaurus, Corythosaurus, Parasaurolophus)

Ceratopsians: large, heavy, powerful, fierce, plant eaters characterized by one or more horns on the face (on the nose and/or over the eyes) and a bony shield protecting the neck (Examples: Monoclonius, Styracosaurus, Triceratops)

Pre-1800: In China, dinosaur bones were called "dragon bones" and were ground up as medicine. In Europe and America, they were thought to be unfortunate victims of the Great Flood (apparently the Ark was all booked up).

Early 1800's: Dinosaur bones were compared with those of modern reptiles, and they were declared to be extinct reptiles, essentially, over-sized lizards. The reconstruction of them as sprawling, slow moving, lizards persisted for many years. In fact, the word "dinosaur" means "terrible lizard."

Circa 1870: American fossil hunters E.D. Cope and O.C. Marsh were great rivals vying for lucrative publicity from big-name museums such as Carnegie and American Museum of Natural History.

"WRONG-HEADEDNESS" AFFECTED MAN AND DINOSAUR ALIKE

The bitter rivalry between former partners Cope and Marsh was legendary. Their respective crews engaged in combat in the field, and they often sabotaged each other's fieldwork. In the rush to be the first to assemble the great dinosaur finds from fossil beds in the Upper Jurassic rocks of Colorado, a skeleton of Brontosaurus at the American Museum of Natural History in New York was given the wrong head (which belonged to Camarasaurus, a stockier cousin), a mistake which stood unchanged for nearly one hundred years!

Early 1900's: Charles Knight murals are painted in the Paleontology Halls of the Field Museum. Some of the scenes depicted include bulky sauropods (Brontosaurus) dragging their tails in a swampy, lake environment. Recent evidence suggests that Brontosaurus (now called Apatosaurus) did not drag its tail on the ground, was not as bulky, and probably lived near forests rather than swamps.

Hollywood established humans and dinosaurs as contemporaries in many films, bridging a gap of some 60 million years. "One Million Years B.C." (1966) extended the existence dinosaurs to the Pleistocene, while "Godzilla" (1956) established new and impossible sizes (200 feet tall) for carnosaurs. The "Flintstones" depicted dinosaurs as beasts of burdens and "living appliances." Barney the Dinosaur is a fixture in childrens' entertainment.

• The largest and best-preserved Tyrannosaurus rex skeleton is found in South Dakota - nicknamed "Sue" and debuts as a blockbuster display at Chicago's Field Museum on May 17, 2000. 
• Tyrannosaurus rex is eclipsed as the largest predator by the discovery of even larger, but unrelated dinosaur predators such as Spinosaurus (seen in the movie Jurassic Park III), and Giganotosaurus
• Dinosaur anatomy has been corrected - dinosaurs are now shown walking upright on erect limbs instead of sprawling with limbs out and bent. [See "Jurassic Park" (1992)]
• Dinosaur physiology debate - Robert Bakker proposes the "hot-blooded" (endothermic), active dinosaur theory in 1975.
• Largest dinosaurs yet found - Jim Jensen begins to unearth Supersaurus and Ultrasaurus, 100 ft. long sauropods in Colorado (1979); David Gillette begins to unearth Seismosaurus (140 ft. long) in Utah (1988)
• Meteorite impact extinction theory proposed by Luis & Walter Alvarez and others (1979)
• Dinosaur egg nests and juvenile skeletons found - Jack Horner proposes that duckbill dinosaurs raised and cared for their young, and lived in communities with other species (ceratopsians) for self protection. Evidence of rapid growth rate in young dinosaurs suggests warm-bloodedness. (1980)

Eoraptor skeleton found (earliest known dinosaur) in Argentina, age dated at 230 million years (1991) 

DINOSAURS - WHY ARE THEY SUCH A BIG DEAL?

Primarily because they were big - they were the largest and most successful land animals ever to live on the earth. Also, they enjoyed a remarkably long (over 150 million years) reign as the dominant fauna - a close look at their past history reveals that they were extremely successful animals.

Children view dinosaurs with great fascination because they are "safe monsters" and because their scientific names are difficult to pronounce by their parents (which delights children greatly).

Adults who are interested in dinosaurs probably had such an interest in their earlier childhood years. For the majority of the public, dinosaurs are the large, monstrous skeletons on display in museums representing untold eons ago. Yet, their conceptions of dinosaurs as a group have probably been colored by Hollywood monster movies, or by outdated dinosaur books aimed primarily at children. In the business world, the word "dinosaur" has come to represent "cumbersome obsolescence" (such as the old style, big, gas guzzling automobiles). 

Plenty - over the last few decades, a "dinosaur renaissance" has been brought about by a new breed of paleontologists looking at field evidence from many disciplines. They are looking at new aspects of dinosaurs, such as their physiology, their lifestyles, their childhood years, and their ecological relationships with each other. Also being debated are previous assumptions of dinosaurs being cold-blooded (ectothermic) and sluggish as modern reptiles are, and the various extinction theories, which invoke some catastrophic cosmic events. Some paleontologists have suggested that dinosaurs were the forerunners of modern birds.  The sheer volume of new dinosaur discoveries has increased, as many finds are being reported in China, and in the U.S. (Dinosaur National Monument in Jensen, Utah), Texas (theropod footprints) and Arizona. Extremely rare discoveries have included dinosaur juveniles, eggs, and very early ancestral forms. The new image of dinosaurs is best seen in the recent Hollywood cinema, such as the movie, Jurassic Park, which was made in consultation with Jack Horner and Bob Bakker, two of the leading dinosaur paleontologists of today.

The popular use of the word dinosaur implies that they were "slow, lumbering, stupid beasts" who deserved to suffer extinction as their fate before "superior mammals." Yet, scientific evidence shows clearly that in direct competition with our mammalian ancestors, the dinosaurs were the superior ones - they dominated the earth for twice as long as the mammals, and were the most intelligent creatures of their time. Yet the dinosaurs still became extinct, probably through no fault of their own. The extinction of the dinosaurs along with nearly one half of all species at the end of the Cretaceous Period is one of the greatest scientific mysteries of all time. Since the Alvarez theory was proposed in 1979, and much debated has ensued, most scientists have come to accept the impact of a 6-mile wide meteorite as the cause of the Cretaceous extinction; the leading lines of evidence found at the Cretaceous-Tertiary boundary include: shocked quartz crystals (stishovite, a form produced only by very high-pressure impact), enrichment of iridium (an element rare on earth, but common in meteorites), and widespread deposits of soot (evidence of huge forest fires). The leading candidate for the location of the impact crater is somewhere in the waters of the Yucatan Peninsulan (near Chixulub) in the Gulf of Mexico, because there is dramatic evidence of overturned late Cretaceous sediments caused by a large impact in water. The debate over the details will still rage on for years to come. The focus of dinosaur paleontologists is not "Why did the dinosaurs become extinct?" but rather, "Why did they last for so long?" Remember that mammals arose almost simultaneously with the reptiles, yet lived in the shadow of the dinosaurs. Only the death of the dinosaurs allowed mammals to fill the ecological vacuum. Some paleontologists believe that were it not for some cosmic catastrophe, the dinosaurs would have continued to evolve, and modern mammals (and man) may not have evolved to their present form.
 

Luis & Walter Alvarez stand before a rock outcrop showing the  iridium anomaly at the Cretaceous-Tertiary (K-T) time boundary