Dinosaurs
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A brief history of dinosaurs
Dinosaurs were a successful group of animals that emerged between 240 million and 230 million years ago and came to rule the world until about 66 million years ago, when a giant asteroid slammed into Earth. During that time, dinosaurs evolved from a group of mostly dog- and horse-size creatures into the most enormous beasts that ever existed on land.
Some meat-eating dinosaurs shrank over time and evolved into birds. So, in that sense, only the non-avian dinosaurs went extinct. (For the purposes of this article, "dinosaurs" will refer to non-avian dinosaurs, unless otherwise stated.)
During the roughly 174 million years that dinosaurs existed, the world changed greatly. When dinosaurs first appeared in the Triassic period (251.9 million to 201.3 million years ago), they roamed the supercontinent of Pangaea. But by the time the asteroid hit at the end of the Cretaceous period (145 million to 66 million years ago), the continents were in approximately the same place they are today.
What are dinosaurs?
The oldest unequivocal dinosaur fossil
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The prehistoric reptiles known as dinosaurs arose during the Middle to Late Triassic Period of the Mesozoic Era, some 230 million years ago. They were members of a subclass of reptiles called the archosaurs (“ruling reptiles”), a group that also includes birds and crocodiles.
Scientists first began studying dinosaurs during the 1820s, when they discovered the bones of a large land reptile they dubbed a Megalosaurus (“big lizard”) buried in the English countryside. In 1842, Sir Richard Owen, Britain’s leading paleontologist, first coined the term “dinosaur.” Owen had examined bones from three different creatures—Megalosaurus, Iguanadon (“iguana tooth”) and Hylaeosaurus (“woodland lizard”). Each lived on land, was larger than any living reptile, walked with their legs directly beneath their bodies instead of out to the sides and had three more vertebrae in their hips than other known reptiles.
Using this information, Owen determined that the three formed a special group of reptiles, which he named Dinosauria. The word comes from the ancient Greek word deinos (“terrible”) and saur
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History & Discoveries
1860
The Rooney family establishes a homestead and begins what would become the largest cattle ranch in Colorado history at the eastern base of the hogback in the early 1860s.
1874
Arthur Lakes finds a Tyrannosaurus rex tooth on South Table Mountain in Golden and recognizes it as belonging to a large carnivorous dinosaur. (T. rex was not named by paleontologists until a partial skeleton was unearthed in Montana in 1905).
1876
The first dinosaur bone fossils are collected from what would become the world-famous Morrison Formation of Late Jurassic age. Some of the most iconic dinosaurs now known lived and died in the area now called Dinosaur Ridge, including Stegosaurus, Apatosaurus, Diplodocus, and Allosaurus, long before the Rocky Mountains uplifted. Arthur Lakes, a professor in Golden, led excavations at 15 quarries along the Dakota Hogback in the Morrison area in search of dinosaur fossils.
1879
Otis Rooney discovers the first horned dinosaur fossils from a gulch near the intersection of the present Alameda Parkway, Bear Creek Bo
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