How Fire Ants in Wyoming Are Uncovering Jurassic Fossils

‘Fire ant nest mound in front of the Morrison Formation. The grey, red and purple banding is indicative of the Morrison Formation in Wyoming’

---

When we think of fossil hunters, we usually picture palaeontologists with brushes and chisels, carefully excavating ancient bones from layers of sediment. But in the grasslands of Wyoming, a surprising new fossil-hunting partner has emerged, Solenopsis invicta, fire ants. These tiny, industrious insects are helping uncover fossils from the Jurassic period, and their contribution is reshaping how we search for prehistoric remains.

Wyoming has long been a hotspot for Jurassic-era fossils, particularly from the Sundance and Morrison Formations, a series of sedimentary rock units of mudstone, shales, and sandstones dating back over 165 to 145 million years. The Morrison Formation has yielded some of the most famous dinosaur fossils in the world, including species like Allosaurus, Stegosaurus, and Apatosaurus, While the Sundance Formation produces abundant marine reptiles and cephalopods. Traditionally, palaeontologists have relied on erosion, surface exposure, and quarrying to find these fossils. But recently, I, like many other palaeontologists, have observed that fire ants are unexpectedly good at bringing fossils to the surface.

Fire ants are known for building complex underground tunnel systems and mounds. In doing so, they often excavate small rocks and debris, which they deposit around the entrances of their colonies. In areas rich in fossil-bearing rock, this means that ants are unknowingly transporting tiny fossil fragments to the surface, often pieces that are difficult to spot without extensive digging and sediment sieving.

In Wyoming, systematic examination of ant mounds in fossil-rich regions results in diverse microfossils, such as dinosaur teeth, fish bones, calcite shells, cephalopods, and fragments of ancient plants. Some mounds contain multiple fossil pieces, offering a more unbiased estimation what lies beneath the surface.

The advantages of this method are significant. For one, it allows palaeontologists to survey large areas quickly without disturbing the landscape. Instead of guessing where to dig, scientists can now prioritise areas where ants have already done the work of excavation. It’s also more environmentally friendly, as it minimises the need for invasive digging in sensitive ecosystems.

---

‘The arid landscape of Wyoming. Laramie Basin. Beneath the ground are Dinosaurs. Within a few miles of this location the remains of Allosaurus, Stegosaurus, and several sauropods have been discovered’

---

Of course, this doesn’t mean ants are replacing traditional fossil-hunting techniques. Rather, they’re providing a useful supplement, especially in places where fossils are deeply buried or spread across wide, arid terrains. As ants tend to colonise specific soil types, their mounds can also give clues about the geological composition of a region, with the ants favouring loose sand rich shales and mudstones.

---

Belemnites (a marine squid like cephalopod) of the Sundance Formation in Wyoming. These are a common sight on the ant mounds.’

---

This collaboration between entomology and palaeontology is a reminder of how interconnected science can be. What started as a curious observation, that ants were collecting calcitic fossils, has evolved into a valuable scientific tool. It also opens up new possibilities: other burrowing animals may be aiding fossil discovery in different parts of the world. Which anecdotally is true of burrowing mammals to determine location of reservoir rocks for oil drilling.

As palaeontologists continue to study fire ants in Wyoming, they’re finding more Jurassic fossils in places they might otherwise have overlooked. These ants, usually thought of as pests, are turning out to be unlikely allies in our quest to understand the ancient past. Sometimes, even the smallest creatures can help us uncover the biggest stories, one fossil at a time

---