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. As a result of their Hollywood exposure, they have become popularly known as "raptors", a name which also refers to other dromaeosaurids.
The Utahraptor could grow up to 7 meters (20 feet) long and weigh almost a ton. A close relative of the Velociraptor, this dinosaur was a fierce predator. Like other dromaeosaurids, it had a huge, blade-like claw on its second toe. With this 20 centimeter talon, it is believed that the Utahraptor could make a deep cut 5 to 6 feet long with one swipe, enabling it to kill dinosaurs much larger than itself.
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.
Although there have probably been dinosaur discoveries dating back thousands of years -- there are, for instance, references to "dragon bones" found in ancient China -- the first documented dinosaur discovery took place in 1676 when a jawbone and teeth were unearthed in Oxford, England. In 1824, famed paleontologist William Buckland (1784-1856) finally named this first dinosaur Megalosaurus. Megalosaurus was a large meat-eater that stood up to 9 meters (30 feet) tall and weighed about 1 ton.
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."
Stegosaurus means "covered lizard" in Greek. This dinosaur had a double row of protective plates covering its back and tail. In addition to acting as a protective covering, these plates may have operated as a sort of cooling device -- wind flowing between the plates would have helped lower the body temperature of a Stegosaurus on hot days. The Stegosaurus is known to have grown as tall as 12 meters (40 feet) and weighed as much as 5 tons.
The Argentinosaurus, an herbivorous sauropod and quite possibly the largest animal ever to walk the earth, is believed to have reached lengths of up to 45 meters (150 feet) and weighed as much as 110 tons! Only fragmentary remains have been discovered, but using their knowledge of related dinosaurs, scientists have been able to estimate the size of these specimens of Argentinosaurus.
An average Tyrannosaurus Rex had arms that were only about 1 meter (3 feet) long. However, with a 1 1/2 meter jaw filled with 50 to 60 nine-inch serrated teeth, the T-Rex may not have needed to use his hands much! Bite marks on other fossils suggest that he could bite through solid bone! And if he broke a few teeth here and there, no big deal -- new ones continually grew in to replace those that he lost. Standing up to 15 meters high and weighing more than 5 tons, Tyrannosaurus Rex was massive -- but he was not the largest carnivorous dinosaur. Giganotosaurus was even bigger.
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.
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.