Tiny fossils reveal big insights about ant ancestors

Two tiny ant fossils recovered in southern Saskatchewan are helping scientists better understand the evolutionary history of modern ants. Ant fossils dating from 72–56 million years ago are rare. What happened to insects such as ants during this period that saw a mass extinction wipe out all non-bird dinosaurs? How did that event reshape their world?

As part of her master’s degree, Elyssa Loewen—in collaboration with researchers Caelan Libke (University of Regina) and Dr. Ryan McKellar (Royal Saskatchewan Museum)—used the Canadian Light Source (CLS) at the University of Saskatchewan to analyze two partial ant fossils. One fossil preserved part of an ant’s head, while the other preserved a partial body.

Both came from the Big Muddy amber deposit, a site that preserves sticky tree resin from an ancient swamp forest that hardened over millions of years into amber, preserving remarkably detailed insects, plants and clues about the environment millions of years ago.

Before the fossils could be imaged, McKellar’s team at the Royal Saskatchewan Museum embedded the amber in epoxy and polished it with rotary tools to expose the insects inside. The samples were scanned using ultrabright X-ray micro-tomography to build detailed 3D models of the ants’ anatomy.

The research team compared the CLS-generated models with modern ant species. Although they were working with only partial fossils, they were able to identify them to specific ant subfamilies that still exist today. Once abundant in North America, these ant groups are now mostly found in the global south. The research was published in the journal Insect Systematics and Diversity.

Clues to an ancient lifestyle

Using a machine-learning model developed by Dr. Christine Sosiak (New Jersey Institute of Technology), another researcher on this project, Loewen and her colleagues also predicted how these ancient ants might have lived. They believe the partial ant head fossil belonged to a group that nested on the ground 67 million years ago, whereas ants from the same family that lived later (post-dinosaur extinction) lived in trees—as do their modern relatives. The finding may suggest that this group experienced an evolutionary shift over millions of years, from life on the forest floor to life in the vegetation canopy.

At the time, the Big Muddy region was a lush, swampy forest filled with metasequoia trees, ferns and flowering plants. These ants would have lived alongside a diverse community of insects just one million years before the end-Cretaceous mass extinction.

Small fossils, bigger ecological questions

Ants are ecosystem engineers, Loewen says. “Understanding how they survived and adapted after the extinction of nonavian dinosaurs helps scientists piece together how modern ecosystems emerged.” Loewen’s work shows that even the smallest fossils can hold big evolutionary discoveries.

The amber samples are now preserved at the Royal Saskatchewan Museum, where they remain available for future research under the supervision of McKellar. Loewen, who now works as a collection technician at the Canadian Museum of Nature in Ottawa, says the team hopes to continue exploring the Big Muddy deposit for more fossils that could shed further light on insect evolution in North America.

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Gaby Clark

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Robert Egan

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