A clear answer
Yes, dinosaurs really existed. Their remains have been found on every continent, including Antarctica, by many independent researchers over roughly two centuries. The evidence is physical and can be examined in museums and universities: bones, teeth, eggs, footprints and more. No serious scientific dispute exists about whether dinosaurs lived; the open questions are about details such as how they behaved, how fast they grew and how their relationships fit together.
The fossil record shows that non-avian dinosaurs, the ones most people picture, lived during the Mesozoic Era, starting roughly 230 million years ago and lasting until about 66 million years ago. That is a vast span of time, far longer than the entire history of our own species, which is only a few hundred thousand years old. So people and the large dinosaurs never lived together.
How scientific knowledge of dinosaurs began
People had long found large bones and wondered about them. Scientific study of these animals took shape in the early 1800s. In Britain, fossils of Megalosaurus and Iguanodon were described by naturalists of the time. In 1842, the anatomist Richard Owen proposed the name Dinosauria, meaning roughly “terrible lizards,” for this group of large fossil reptiles. Since then, thousands of species have been described, and new ones are still named every year.
How fossils form
A fossil is any preserved trace of ancient life. Fossilization is rare, because most animals that die are eaten, scavenged or decay completely. For bones to be preserved, a few conditions generally help:
- The animal is buried quickly, for example by sediment from a flood or river, which protects it from scavengers and weathering.
- Water carrying dissolved minerals seeps through the buried bone. Minerals can fill tiny spaces in the bone, or slowly replace the original material, a process often called permineralization or replacement.
- Over long periods the sediment hardens into rock, which is part of the rock cycle that turns loose sand and mud into sandstone and shale.
- Erosion or uplift later exposes the rock, and someone finds the fossil.
Because this takes so many chance events, the fossil record is incomplete. Scientists generally believe that many species left no known fossils at all. This is one reason new discoveries keep changing our picture of dinosaur diversity.
Many kinds of evidence
Dinosaurs are not known from one lucky find. Several different kinds of evidence point the same way:
- Skeletons. Partial and nearly complete skeletons, often of several individuals of the same species, show consistent anatomy.
- Teeth. Because teeth are hard, they fossilize well and show what an animal ate, from sharp, blade-like teeth to flat grinding ones.
- Footprints and trackways. Sets of footprints preserved in ancient mud record how animals moved, how big their stride was and sometimes whether several traveled together.
- Eggs and nests. Fossil eggs and clutches, some containing embryos, show how dinosaurs reproduced.
- Coprolites. Fossilized droppings give clues about diet.
- Skin and feather impressions. In rare, exceptionally preserved fossils, especially from northeastern China, impressions of feathers and scales survive.
These lines of evidence support one another. A set of footprints, for example, can be matched to the foot bones of a species found in the same rock layers.
How fossils are dated
Scientists use two main approaches. The first is relative dating. Rock layers generally build up from the bottom, so fossils in lower layers are usually older than those in layers above. Matching distinctive fossils across distant sites helps correlate layers.
The second is absolute dating, which gives an age in years. Dinosaur bones themselves are usually not dated directly. Instead, scientists date volcanic rock, such as ash layers, found above and below the fossil. Certain minerals in volcanic rock contain unstable forms of elements called atomic isotopes, which decay into other elements at known, steady rates. By measuring how much of the original material remains, researchers can estimate when the rock formed, and so bracket the age of the fossil between two dates. Using several methods and checking them against each other reduces the chance of error.
Fossils also appear in the places you would expect given the movement of continents. Related dinosaur groups are found on landmasses that are now far apart but were once connected, which fits with plate tectonics.
What happened to the dinosaurs
The large non-avian dinosaurs disappeared at the end of the Cretaceous Period, about 66 million years ago. The best-supported explanation is that a large asteroid struck what is now the Yucatán Peninsula in Mexico, with intense volcanic activity in India and changes in climate likely adding to the stress. Scientists continue to refine how these factors combined. This was a mass event of species extinction that also removed many other kinds of life, although some groups survived, including small mammals and early birds.
Dinosaurs are still with us
One of the best-supported findings in paleontology is that birds are a living group of dinosaurs. Many fossils show feathers, wishbones and bird-like skeletons in small, two-legged predators, and these features link the older forms to birds. So when you see a sparrow or a chicken, you are looking at a descendant of dinosaurs. This is part of the broader history of how life changed over time.
Common questions
Why do we see only bones in museums? Bones and teeth are what usually survive. Many displays also include casts and reconstructions based on the real fossils, with colors and some soft features being informed guesses.
Do scientists ever get things wrong? Yes, and they correct them. Early reconstructions of some species were revised as more complete skeletons were found. That process of revision is how the science works, and it does not undermine the basic conclusion that these animals lived.
Could any dinosaurs still be alive besides birds? There is no evidence of any non-avian dinosaurs surviving to the present.