How did dinosaurs leave their footprints in solid rock?

Imagine standing at the base of a towering rock face, gazing up at a network of dinosaur tracks seemingly impossibly etched high above. Not only are these tracks preserved in stone, but they also stretch across an almost vertical surface.

The story behind these tracks begins with a simple stroll on the shore. Long ago, dinosaurs left their impressions in wet sediment, typically along a beach, mudflat, or the shallow sea's floor. As the soil dried, the tracks solidified. Over time, additional layers of sediment filled in these prints, safeguarding them from erosion. Heavy dinosaurs, with their powerful steps, could even create ‘underprints’—deep impressions in the soil that were shielded beneath the surface.

Over millions of years, these sediment layers turned into sedimentary rock, the same kind that preserves the bones of dinosaurs. Eventually, erosion, weathering, and geological processes exposed these hidden tracks. In some places, these forces dramatically altered the landscape, tilting it from horizontal to vertical.

For dinosaur tracks to survive for millions of years, certain conditions had to be met. The sediment the dinosaurs walked through needed to have the perfect texture—not too soft, not too hard. Tracks in excessively wet soil would collapse, while those in overly firm soil wouldn’t leave clear impressions. The sediment filling the tracks also had to fall slowly and be a different type than the surrounding soil. For example, ash from a distant volcano would preserve the tracks better than a sudden mudslide that covered the prints. And of course, geological forces had to align in just the right way for the tracks to be exposed today.

Dinosaur tracks have been found on every continent except Antarctica, though they remain relatively rare. However, their scarcity and longevity are not the most astonishing aspects. Paleontologists can often deduce the actions of dinosaurs from their tracks, revealing behaviors that skeletal fossils sometimes can’t. Continue to the next page to learn more.

Trackways and Trace Fossils

A dinosaur’s skeleton can tell you a great deal about its appearance and some aspects of how it moved or ate. But to truly understand how a dinosaur lived, you must turn to trace fossils. Also called ichnofossils, trace fossils preserve evidence of how organisms interacted with their environment. For dinosaurs, these include tracks, nests, eggs, burrows, and coprolites—fossilized feces.

Trackways, or sequences of two or more consecutive footprints, serve as valuable records for paleontologists. For instance, many of the trackways found thus far do not exhibit the snake-like impressions typically left by a tail dragging across the ground. This suggests that the dinosaurs responsible for the tracks kept their tails elevated. The absence of drag marks also indicates that these dinosaurs maintained their bodies upright over their legs, similar to horses, rather than splaying their legs like alligators.

Researchers can also estimate the speed of a dinosaur by measuring the length of its tracks and the spacing between them. In general, if the stride is more than four times the length of the foot, it indicates the dinosaur was running rather than walking. Additionally, scientists have employed computer simulations to analyze the tracks and estimate the height of the dinosaur's hip [source: Henderson].

Trackways provide more than just insight into how a single dinosaur moved; they can also reveal social behaviors. However, this isn't always the case for trackways with numerous overlapping prints, such as those found at the Davenport Ranch site in Texas. This location holds the tracks of 23 different sauropods—herbivorous, four-legged dinosaurs [source: American Museum of Natural History]. While some researchers believe smaller dinosaurs may have followed in the tracks of larger ones, it remains unclear how much time passed between the formation of each set of prints.

However, collections of parallel tracks moving in the same direction, like the ones shown above, suggest that some dinosaurs might have traveled in groups. A single set of tracks that spans a large area with minimal overlap could indicate that the dinosaur was methodically searching for food.

One crucial detail that trackways often cannot provide is the specific dinosaur that left them. Very large dinosaurs had thick muscles and cushioning on their feet, so their preserved footprints don’t resemble the bones that scientists use for identification. Additionally, because bones fossilize best when they are quickly buried, and tracks preserve more effectively when covered slowly, it is uncommon for researchers to find tracks alongside the actual skeleton of the dinosaur that made them.