A “track” is a print made by a single foot. The footprints made during a single creature’s journey are called a trackway. A “trail” is a print left behind by an animal that moves around without legs. A snake, for instance, would leave behind a long, curvy trail. Dinosaur trackways can become fossils too, and survive for millions of years. Paleontologists study dinosaur trackways carefully. They can tell you a lot about the dinosaurs that made them. For instance, you can see how many toes it had, which toes carried most of its weight, whether there were pads on a dinosaur’s foot, or whether or not it had claws. You can see whether the dinosaur was bipedal, meaning that it walked on two legs, or whether it was a quadruped, meaning that it walked on all four legs. You can also tell how fast it was moving. The study of fossil footprints is called “ichnotaxa”.
A large sauropod such as a Brontosaurus would leave two kinds of prints: a larger, heavier print from the back legs and a smaller, lighter print from the front legs. This tells you that the back legs carried most of the weight of the dinosaur. A small theropod dinosaur walked on two feet and would leave a lighter trackway that wouldn’t press as deeply into the earth. This tells you that it wasn’t a very heavy dinosaur. Larger theropods left heavier prints. They walked on two legs and had three large toes. You can also see that they didn’t drag their tails on the ground, but held them up for balance.
By measuring the space between footprints, we can see how fast a dinosaur was moving. If the space between prints is four or more times the track length, we can tell that the dinosaur was running. If the prints are close together, we can see that the dinosaur was walking slowly or wading through water. Huge sauropod dinosaurs with short legs and big bodies – such as Apatosaurus, Diplodocus and Brachiosaurus – were probably the slowest of the dinosaurs. Massive, heavily plated dinosaurs like the Ankylosaurus were also slow, although a new trackway found in Bolivia, South America shows that ankylosaurs weren’t as slow as many people thought. The fastest dinosaurs were the bird-like, bipedal carnivores such as Gallimimus, Coelophysis and Velociraptor. These speedy dinosaurs were probably about as fast as a tiger or an ostrich. They could run about 43 mph.
Dinosaur skeleton fossils are best preserved when they are buried quickly, like in a mudslide or earthquake. Trackways, on the other hand, are best preserved when they are buried slowly and gently. Some of the best trackway fossils are made when a dinosaur walks across soft mud. The tracks then become dry and hard in the sun. A little bit later, the prints are buried in sand or a different kind of mud. The prints are buried under layer after layer of sand over millions of years. The original mud turns to stone and becomes a fossil. Millions of years later, the tracks are brought back to the surface again by an earthquake or rising mountains. Many times, dinosaur trackways are found by accident. They are often found when people are digging for other kinds of stone. Sometimes, paleontologists are lucky to find lots of tracks at once. In Lark Quarry, in the Australian outback, an entire dinosaur herd stampede was found.