What's A Dinosaur?
The top picture shows Megalosaurus in the days of Richard Owen. The parts in red show all the bones they had at this time. The bottom picture shows a modern version of Megalosaurus.
When you think of a dinosaur, what comes to mind? Do you think of the deadly T. rex, or the huge plant-eating brontosaurs? All of us seem to know what one looks like, but what is a dinosaur? This is a question that has been very confusing.
It all started in the early 1800s when people discovered the fossil remains of animals that looked like giant lizards. Richard Owen, a British scientist, decided to call these creatures "dinosaurs." This is a name made up from two Greek words: deinos (DIE-noss), for "terribly great," and sauros (SAW-ross), for "lizard." Often we read that deinos means "terrible," as in "fearsome" or "horrible," but Owen used the word to mean "extremely big."
As it turns out, some of the dinosaurs were not that big, and they were not lizards either. In the early days, people knew that these strange creatures had to be a type of reptile. The fossils sure looked as though they belonged to giant lizards. But as more bones turned up, scientists realized that the dinosaurs were different. Unlike lizards, dinosaurs walked with their legs right below the body, which kept their bellies off the ground.
Today, some scientists use ideas about evolution to define the word "dinosaur." They say that the group of animals known as the Dinosauria includes any animal descended from the common ancestor of Triceratopsand birds. But this is a bad definition, because it is not true that birds are the modern versions of two-legged dinosaurs. No one knows how scales can turn into true feathers, or how delicate arms can turn into powerful wings. Dinosaurs do not live today because they are extinct.