The signs of ancient animals
It’s not only the actual body parts of dead animals and plants that can become fossils. Trace fossils are tracks and burrows made by animals as they went about their lives millions of years ago. Dinosaur footprints are probably the most dramatic trace fossils but many others tell fascinating stories.
Many trace fossils have been found along the Jurassic Coast. They provide essential information about what it was like here when the rocks were forming. They can also give clues about the behaviour of the creature that made them, whether walking, crawling, burrowing or feeding.
Dinosaur footprints come in all shapes and sizes, some as obvious trackways, others as a jumble of prints. They were created when a dinosaur made tracks in muddy ground by lakes, rivers and swamps. After the impressions were left, the mud was baked hard and then the impression was filled in with more mud. Eventually these sediments hardened into rock, creating a cast, or mould, of the original print.
So why have far more dinosaur tracks been found than dinosaur bones? The answer is simple – each individual dinosaur made millions of footprints in its time, so there are far more footprints than dinosaurs.
The footprint to the right was probably made by an iguanadon.
Fossil poo (coprolites) can tell us a lot about what dinosaurs and marine creatures ate. They are packed with undigested food remains such as fish scales and sometimes the bones of other reptiles. You can clearly see fish scales in the two coprolites on the right.
Burrows and borings
One of the largest types of trace fossil is Thalassinoides, a branching burrow system made by a shrimp. Today identical burrows are being made by shrimps that live in shallow tropical or semi-tropical water.
Another type of trace fossils are borings, where animals like worms or bivalves have drilled into shells and even hard rock. This photo shows linear marks possibly made by a shrimp as it dug in the mud. Below are worm burrows.