Fossils

Let’s learn about trace fossils

Ancient creatures’ burrows, footprints, poops and piles of vomit offer clues into their daily lives

These Ankylosaurus dinosaur footprints are trace fossils. They preserve the story of an ancient animal’s walk through what is now the Wide Toro Toro National Park Valley in Potosi, Bolivia.

Alexandre Morin-Laprise/Getty Images

By Maria Temming

When you hear the word “fossil,” you might at first think of a dinosaur skeleton at your local museum. Or perhaps the imprints of leaves or shells in a rock from a nearby creek. Both are examples of body fossils. But there is a second type of fossil: trace fossils.

Body and trace fossils are created through similar processes. In both cases, some trace of an ancient life form is left in sediment. That remnant gets preserved when the sediment transforms into hard rock. But while body fossils preserve the remains of ancient life forms themselves, trace fossils keep a record of those life forms’ activities. Examples include burrows, nests, footprints, poop and vomit.

Ichnologists use trace fossils to obtain snapshots of ancient life forms’ daily lives that these scientists can’t get from remains alone. Take, for instance, fossilized poop, called a coprolite. Coprolites can offer clues about an ancient creature’s diet.

Fossil dung has revealed that, more than 150 million years ago, flying reptiles called pterosaurs ate mollusks and crustaceans. These fossils have also shown that tens of thousands of years ago, squirrels may have snacked on the remains of woolly mammoths and wolves.

Dietary info can also come from fossil vomit, known as regurgitalite, and fossilized stomach contents, called cololites.

The marks that ancient animals carved into their environments can also make useful trace fossils. Rocks from coastal Taiwan, for example, contain burrows likely dug by giant worms some 20 million years ago. Those lairs suggest that the worms lurked beneath the seafloor like Star Wars monsters and shot out to attack their prey.

Scientists have also studied dinosaurs’ footprints to tease out details like how fast they ran.

Want to know more? We’ve got some stories to get you started:

New clues about dino speed come from birds strutting through mud Scientists use dinosaurs’ tracks in wet ground to estimate how fast they ran millions of years ago. (8/22/2025) Readability: 6.4

Frozen poop reveals Ice Age squirrels’ ecosystem DNA stored in ancient scat shows the Yukon rodents ate their way through the food chain. (8/25/2026) Readability: 6.8

Giant worms may have hidden beneath the ancient seafloor to ambush prey Trace fossils may be evidence of predatory behavior similar to modern bobbit worms. (2/16/2021) Readability: 8.1

There are two main categories of fossils: body fossils and trace fossils.

Explore more

Scientists Say: Ichnology

Scientists Say: Coprolite

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Fossil vomit shows what one 290-million-year-old predator dined on

New fossils bring the wide world of pterosaurs to life

Fossil stomach reveals a dinosaur’s last meal

New beetle species found in fossil poop of this dino relative

A love of small mammals drives this scientist

The secret to T. rex‘s incredible biting force is at last revealed

Activities

Word find

Want to see how easy it is for ancient life forms to leave traces behind? Make your own trace fossil with instructions from the Natural History Museum of Los Angeles County.

Power Words

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cololite: Term for fossilized contents of an animal’s digestive tract.

coprolite: Fossilized feces. The word coprolite, in Greek, means “dung stones.” Coprolites are very important because they can provide direct evidence of what ancient creatures ate.

crustaceans: Hard-shelled water-dwelling animals including lobsters, crabs and shrimp.

diet: (n.) The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. Sometimes this is a specific food-intake plan.

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. The lizard-hipped line are believed to have led to the saurischians, such as two-footed theropods like T. rex and the lumbering four-footed Apatosaurus. A second line of so-called bird-hipped, or ornithischian dinosaurs, appears to have led to a widely differing group of animals that included the stegosaurs and duckbilled dinosaurs. Many large dinosaurs died out around 66 million years ago. But some saurischians lived on. They are now the birds we see today (and who have now evolved that so-called “bird-hipped” pelvis).

dung: The feces of animals, also known as manure.

environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

extinct: (n. extinction) An adjective that describes a species for which there are no living members.

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.

ichnologist: A scientist who studies trace fossils such as footprints, burrows or chew marks on bones.

mollusks: Soft-bodied invertebrate animals that usually live in water and develop a hard protective shell. Examples include snails, shellfish (like clams and oysters), slugs, octopuses and squids.

predator: (adjective: predatory) A creature that preys on other animals for most or all of its food.

prey: (n.) An organism hunted by another, often for food. (v.) To attack and eat another organism.

pterosaur: Any of various extinct flying reptiles of the order Pterosauria. These animals lived 245 million years ago to 65 million years ago. Although not true dinosaurs, they lived during the reign of dinosaurs. Among members of this order were the pterodactyls of the Jurassic and Cretaceous periods, which were characterized by wings consisting of a flap of skin supported by the very long fourth digit on each forelimb.

regurgitalite: The scientific term for fossilized vomit.

relic: Something that is a leftover from an earlier time. The term is usually applied to things that had been fashioned by people.

reptile: Vertebrate animals belonging to a group known as Reptilia. Most reptiles have skin that is covered with scales or horny plates. Snakes, turtles, lizards and alligators are all reptiles. Once considered their own separate group, birds now belong to this order. With the exception of modern birds, most modern reptiles are cold-blooded (or ectothermic).

shell: The normally hard, protective outer covering of something. It could cover a mollusk or crustacean (such as a mussel or crab), a bird’s egg or some other relatively soft tissue that needs protection (such as a tree nut or peanut).

trace fossil: Evidence other than a preserved carcass or bones of ancient life. Footprints, burrows or chew marks on a bone are examples of such trace fossils. These can provide information that’s more valuable than body fossils. For instance, trace fossils can hint at a creature’s behavior. Evidence of that is usually scant.

woolly mammoth: A type of extinct mammal that resembled a hairy elephant.

About Maria Temming

Maria Temming is the Assistant Managing Editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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