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Trace fossils, or ichnofossils, serve as a window into ancient life, capturing evidence of animal behavior from the past. Unlike traditional fossils that depict an animal's remains, trace fossils illustrate how creatures lived and interacted. These fossils come in various forms, such as preserved burrows, footprints, trails, nests, eggs, and even fossilized excrement. Exploring these sites provides a unique opportunity to delve into the discoveries scientists have made through these remarkable remnants.
1. FOOTPRINTS OF THE PAST
Replica of the Laetoli footprints displayed at the Smithsonian Museum of Natural History in Washington, D.C. Image by Tim Evanson, Wikimedia // CC BY-SA 2.0
Footprints stand out as some of the most compelling trace fossils, offering a direct connection to our ancient predecessors. Some are fleeting, like those discovered in 2013 in Norfolk, England, where researchers from the British Museum observed that stormy seas had stripped away silt layers, revealing estuary mud marked by prehistoric footprints. Although these 800,000-year-old prints vanished within weeks due to erosion, they were meticulously recorded through digital imagery for ongoing study. Others have endured much longer: a set recently unearthed in British Columbia could be 13,200 years old, potentially making them the oldest footprints in North America.
Where to see them: The Laetoli trackway in Tanzania is the most renowned site for footprint trace fossils. Here, 3.6-million-year-old footprints of early hominins were discovered, providing evidence of upright walking in our ancestors. While the actual trackway is off-limits to visitors, a replica of the footprints is on display at the nearby Olduvai Gorge Visitor Centre.
2. TRACES OF ANCIENT MOVEMENTS
Climactichnites and ripple marks from Wisconsin, exhibited at the National Museum of Nature and Science in Tokyo. Image by Momotarou2012, Wikimedia // CC BY-SA 3.0
Among the most fascinating trace fossils are preserved trackways found in sediment. Since these tracks are rarely accompanied by the fossilized remains of the animals that made them, identifying the specific creature can be challenging for scientists. In cases involving soft-bodied organisms like worms—which lack skeletons and leave no bodily fossils—trace fossils of their trails are the sole evidence of their existence. These trackways, formed where the creatures lived and moved, often provide valuable insights into their habitats and behaviors.
3. ANCIENT ANIMAL HABITATS
Asteriacites from the Devonian period in northeastern Ohio. Image by Mark A. Wilson, Wikimedia Commons // Public Domain
Asteriacites
, the fossilized burrows of starfish or ophiuroids, are among the most visually striking trace fossils. Predominantly found in Jurassic rock layers, these impressions are formed when starfish press their arms into soft sediment. They are particularly valuable to researchers, as they can capture detailed imprints of the animal's body. Trilobites also leave behind similar resting traces, adding to the diversity of these ancient records.
Burrow trace fossils are most commonly linked to small marine creatures or bivalves, like clams, that dug into the seabed.
Where to see them: An Asteriacite fossil is on display at the Peabody Museum of Natural History at Yale University in Connecticut, home to a globally acclaimed Invertebrate Zoology department.
4. TRACES OF ANCIENT FEEDING
Bitemarks preserved in fossils can reveal beavers constructing dams, insects feeding on leaves, or, in more dramatic instances, dinosaurs preying on one another. Identifying the predator based solely on tooth marks is often challenging, but occasionally, a fragment of a tooth left in the bone provides clues. For example, a pterosaur bone discovered in Alberta, Canada, bore gnaw marks and a partial tooth, later identified as belonging to the Saurornitholestes, a Late Cretaceous dinosaur resembling the well-known Velociraptor from Jurassic Park.
Where to see them: The La Brea Tar Pits in Los Angeles showcase remarkably preserved Ice Age fossils, some displaying bite marks from insects and rodents.
5. TRACES OF ANCIENT BIRTHS
The classification of eggs as trace fossils or body fossils is debated. When embryonic material is preserved inside, they are considered body fossils. However, fossilized nests provide valuable insights into the nesting behaviors of dinosaurs and other creatures. Dinosaur nests have only been discovered on the ground, indicating they nested similarly to modern reptiles and birds like penguins.
Where to see them: The Natural History Museum in London features a nest belonging to a Protoceratops, a small horned dinosaur. This nest, along with a clutch of eggs, was unearthed in Mongolia's Gobi Desert and dates back over 80 million years.
6. FOSSILIZED WASTE
A coprolite named "Precious," found in South Carolina and exhibited at the Poozeum. Image courtesy of Poozeum, via Wikimedia Commons // CC BY-SA 4.0
Fossilized animal droppings, known as coprolites, provide significant insights into their dietary habits, distinguishing between herbivores and carnivores. For instance, the coprolites of Tyrannosaurus rex suggest they consumed their prey entirely, including bones. The term 'coprolite' was first introduced by geologist William Buckland in 1829 after he identified peculiar fossilized formations as feces. In 2014, a 40-inch long coprolite fetched $10,370 at auction, though some experts argue it might be a misidentified lump of siderite mineral.
Best Places to View Coprolites
The South Florida Museum in Bradenton houses the world's most extensive coprolite collection, affectionately called the 'poozeum.' This remarkable assembly includes 1,277 specimens gathered from eight countries and 15 states.
