Velociraptor means "fast thief." This fast-running dinosaur, which lived during the late Cretaceous period (about 85-80 million years ago), has become quite popular due the movie Jurassic Park. Standing only about 3 feet tall (and 5 to 6 feet long), Velociraptors were much smaller than depicted in the movie. They were, however, fierce predators, and their sickle-shaped talons could reach the length of the teeth on sabertooth cats, making them a formidable adversary.

When famed paleontologist Othniel Charles Marsh first discovered a Triceratops fossil in 1887, he mistakenly identified it as a type of bison. Another Triceratops fossil was discovered a year later by John Bell Hatcher, and in 1889, Marsh, realizing his mistake, finally named this dinosaur. Triceratops, which is believed to have lived in herds much like modern buffalo, had three distinctive horns -- one on its snout and two more above the eyes. Along with the bony frill that protected the rear of its skull, these horns provided a natural defense against the attacks of other dinosaurs, but the Triceratops was himself an herbivore, feeding on plants and shrubbery with his sharp beak.

Dinosaurs are believed to have become extinct about 65 million years ago, at the end of the Cretaceous period. We know of their existence today because of fossilized remains -- mostly bones, but in a few cases impressions of skin, feathers, and even internal organs. It is impossible to know for sure what caused this sudden mass extinction, but the prevailing theory is that a massive meteor struck the earth about that time causing drastic climate changes and thus the extinction. Other theories of dinosaur extinction involve decreasing oxygen levels in the atmosphere, natural climate changes caused by increased volcanic activity, or perhaps a massive "belching" of methane gas from below the surface of the ocean.

Dinosaurs diverged from their archosaur ancestors during the middle to late Triassic period. Living representatives of the Archosaurs include birds and crocodilians.

Scientists estimate that the average lifespan of a T. rex was only 20-30 years, but some of the larger Sauropods may have lived 100 years or more.

Many scientists believe that a massive meteorite hit the Yucatan Peninsula of Mexico 65.5 million years ago and caused the extinction of the dinosaurs.

In 1877, a paleontologist named Othniel Charles Marsh (1831-1899) discovered a new species of dinosaur with he named Apatosaurus, meaning "deceptive lizard." Two years later, he discovered what he believed to be another species of dinosaur. He named this one Brontosaurus, meaning "thunder lizard." When later paleontologists examined the two fossils, however, they determined that both skeletons belonged to the same animal class, one being an adult and one being a juvenile. Since the Apatosaurus was discovered and named first, it became the official name. The Brontosaurus, however, had captured the imagination of the public and continued to be preferred by the general public. It was not until the 1980s, when the United States Post Office was taken to task by paleontologists for issuing a stamp depicting the creature and using the improper name, that people even began to be aware of the controversy. Since that time, most dinosaur literature has begun using the proper name Apatosaurus, often with a footnote that these massive dinosaurs used to be called "Brontosaurus."

The Brachiosaurus, a herbivore, used its giraffe-like neck to graze in the tops of trees. It is believed to have reached heights of up to 13 meters (42 feet), lengths of 25 meters (82) feet, and weights in excess of 90 tons. Once considered the largest known dinosaur, it has since been surpassed by the likes of Argintinosaurus and Sauroposeidon.

Until the late 20th century, all groups of dinosaurs were believed to be extinct. However, the fossil record indicates that birds are the modern descendants of feathered dinosaurs, having evolved from theropod ancestors during the Jurassic Period.

Kosmoceratops had fifteen horns or horn-like structures on its skull, the most of any ceratopsian. Its name means "ornate horned face".