Scientists Say Life

Scientists Say: Ichnology

Rather than study organisms themselves, this field looks at marks they left behind

A scientist places her hand alongside a fossilized dinosaur track, an example of a trace fossil.

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By Katie Grace Carpenter

Ichnology (noun, “ICK-nawl-uh-jee”)

Ichnology is a branch of science that studies tracks, burrows and materials left behind by living things. These left-behind clues are called traces.

Ichnology doesn’t study the bodies of living things. Nor does it study the fossilized remains of past life, such as bones. Instead, ichnology looks at the way those living things changed their surroundings. Such changes may include tracks through the mud or burrows in sediment.

A scientist who studies traces is called an ichnologist. Many ichnologists study fossilized traces. Fossil traces can tell us about the environment in a particular region when the fossils formed. Trace fossils might tell us whether a region was once a marsh or a deep ocean basin. That’s because different living things inhabit these two places. And they each leave behind their own clues. These clues can tell us about the past water depth, salinity, light level and more.

Other ichnologists study modern traces. This information can help scientists better understand the past as well as the present. Here’s an example. Marine animals, such as clams, live in burrows they dig in the ocean floor. If the environment changes — the temperature cools, or food becomes less available — they may dig a deeper burrow or move to a new spot. We can’t directly measure things like temperature or food availability hundreds of thousands of years ago. But comparing patterns in fossilized burrows with clam burrows today may give us clues about the environment those ancient animals lived in.

Ichnology goes back a long time. Consider the ancient humans who hunted animals by looking at their tracks. They were already using the science of ichnology.

In a sentence

To figure out that the duck-billed dinosaurs called hadrosaurs lived in herds, scientists looked to the field of ichnology and studied fossilized dinosaur tracks.

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basin: (in geology) A low-lying area, often below sea level. It collects water, which then deposits fine silt and other sediment on its bottom. Because it collects these materials, it’s sometimes referred to as a catchment or a drainage basin.

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).

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).

field: An area of study, as in: Her field of research is biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.

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.

hadrosaur: A duck-billed, plant-eating dinosaur that lived during the late Cretaceous Era.

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

information: (as opposed to data) Facts provided or trends learned about something or someone, often as a result of studying data.

marine: Having to do with the ocean world or environment.

marsh: A low-lying wetland usually covered with grasses and shrubs, not trees. It’s a prime feeding and nesting ground for waterfowl.

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

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.

About Katie Grace Carpenter

Katie Grace Carpenter is a science writer and curriculum developer, with degrees in biology and biogeochemistry. She also writes science fiction and creates science videos. Katie lives in the U.S. but also spends time in Sweden with her husband, who’s a chef.

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