Illustration © Doug Henderson
Around 66 million years ago, a wide range of large dinosaurs roamed the continents, while winged reptiles called pterosaurs flew overhead. By 65 million years ago, the pterosaurs, most of these dinosaurs and many other land animals had vanished. The age of the dinosaurs, which had lasted 170 million years, was over. Certain types of mammals were especially hard hit, although other mammals--such as an early relative of all primates, including humans--survived. A variety of plants also went extinct at this time.
Illustration: Mark Hallett
- Tyrannosaurus Rex: T. rex was a theropod: a two-legged, meat-eating dinosaur. The first theropods appeared more than 200 million years ago.
- Sauropods: Giant, long-necked, plant-eating sauropods flourished in the Jurassic but died out 65 million years ago.
- Triceratops: The family of horned dinosaurs, which included Triceratops and more than a dozen other species, was common across western North America.
- Other Dinosaurs: Dome-headed dinosaurs, armored dinosaurs and duckbilled dinosaurs went extinct around 65 million years ago.
- Pterosaurs: The flying reptiles named pterosaurs are not dinosaurs or birds. Pterosaurs first appeared almost 230 million years ago.
- Mammals: Marsupials and multituberculates were both hard hit. Kangaroos are modern marsupials.
- Plants: In some regions, between 30 and 50 percent of plant species went extinct.
End of the Duckbills
Duckbilled dinosaurs, known as hadrosaurs, were large, two-legged, plant-eating dinosaurs. All hadrosaurs died out around 65 million years ago.
A Drop in Numbers
Were the dinosaurs struck down suddenly in their heyday? Or were they dwindling in number well before the last nonavian dinosaurs died out 65 million years ago? The available evidence--and frustrating gaps in the fossil record--make it difficult to answer these questions.
A careful survey of currently known fossils suggests that dinosaur diversity peaked roughly 80 million years ago then slowly declined. But fossil sites from this time period are scarce. The decrease in dinosaur diversity we see in the fossil record could reflect a drop in the number of dinosaurs, a drop in the number of fossil sites--or both. Future discoveries should help us understand more about the end of nonavian dinosaurs.
Skin, Not Bones
Fossils aren't always bones. Sometimes fossil hunters turn up imprints of an animal's skin. Some fossils show the pattern of raised bumps, or tubercles. These have been found on a duckbill dinosaur called Lambeosaurus, which lived about 80 million years ago--around the time when the diversity of dinosaur species seems to have been greatest.
North American Dinosaurs
Like most fossils from the end of the age of dinosaurs, a skull of a dome-headed dinosaur was found in western North America. Does this mean that dinosaurs lived only in North America near the end of their reign? Probably not. Across the globe, 65-million-year-old sediments aren't exposed as they are in North America. Researchers have yet to find dinosaurs from this era on other continents.
An Early End
Very few fossils of Daspletosaurus, a relative of Tyrannosaurus rex, have been found. Researchers think that perhaps this dinosaur died out a few million years before T. rex, which disappeared along with all other nonavian dinosaurs 65 million years ago.
A wide range of dinosaurs, including armored dinosaurs, tyrannosaurs, duckbills and horned dinosaurs, inhabited western North America some 75 million years ago. Dinosaur diversity seems to have peaked around this time.