dinosaur: A term that means terrible lizard. These reptiles emerged around 243 million years ago. All descended from egg-laying reptiles known as archosaurs. Their descendants eventually split into two lines. For many decades, they have been distinguished by their hips. Many large dinosaurs died out around 66 million years ago. But some live on. They are now the birds we see today.

fossil: Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

gauge: A device to measure the size or volume of something. For instance, tide gauges track the ever-changing height of coastal water levels throughout the day. Or any system or event that can be used to estimate the size or magnitude of something else. (v. to gauge) The act of measuring or estimating the size of something.

high school: A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.

paleontologist: A scientist who specializes in studying fossils, the remains of ancient organisms.

paleontology: The branch of science concerned with ancient, fossilized animals and plants. The scientists who study them are known as paleontologists.

recall: To remember.

sediment: Material (such as stones and sand) deposited by water, wind or glaciers.

species: A group of similar organisms capable of producing offspring that can survive and reproduce.

toddlers: Children between 9-months and 2-years old. The term refers to the fact that these youngsters only recently learned to walk and are not yet totally steady on their feet.

trackway: Three or more consecutive footprints left behind by an animal. The spacing and arrangement of individual prints can provide clues about such things as how large a creature had left them and how fast it had been moving.

Tyrannosaurus rex: A top-predator dinosaur that roamed Earth during the late Cretaceous period. Adults could be 12 meters (40 feet) long.

unique: Something that is unlike anything else; the only one of its kind.

vertebrate: The group of animals with a brain, two eyes, and a stiff nerve cord or backbone running down the back. This group includes amphibians, reptiles, birds, mammals and most fish.