Scientists Discover Oldest Ever Fossilized Army Ant

by Amy Myers

Scientists have once again proven that even small discoveries can have a massive impact. Recently, researchers at the New Jersey Institute of Technology (NJIT) and Colorado State University have found a fossilized army ant (Dorylinae) dating back to the Eocene, roughly 35 million years ago. This makes the Baltic amber-coated ant the oldest ever fossil of its kind.

At just three millimeters in length, army ants have marched their way across the globe, making their mark on most of the seven continents. Thanks to the latest discovery, researchers have now concluded that the list of native habitats also includes Europe. This new fossilized army ant helps scientists draw a direct connection to previously unknown species lineages across Europe before their inevitable extinction within the past 50 million years.

Perhaps most surprising of all is the fact that this crucial specimen was not at all a new excavation. In fact, the fossil has lived in the Museum of Comparative Zoology at Harvard University since 1930. Luckily, the army ant finally fell into the hands of the paper’s lead author and NJIT Ph.D. candidate, Christine Sosiak, who was able to correctly identify the insect’s real age.

“This amber would have been excavated around or before the 1930sso to now learn it contained a rare army ant is surprising enough, much less one that demonstrates these ants roamed Europe,” said Phillip Barden, senior author of the paper as well as the assistant professor of biology at NJIT. “From everything we know about army ants living today, there’s no hint of such extinct diversity.”

Fossil Is First Physical Evidence of Army Ant Syndrome in Europe

According to Barden, the new information about the specimen provides a “rare paleontological porthole” into the history of tiny predators. And with 270 current Dorylinae species in the Eastern Hemisphere, this new perspective is nothing short of incredibly valuable.

“At the time the fossil formed, Europe was hotter and wetter than it is today and may have provided an ideal habitat for ancient army ants,” said Barden. “Europe underwent several cooling cycles over tens of millions of years since the Eocene, however, which may have been inhospitable to these tropical-adapted species.”

Most notably, the team reported that the specimen possessed an enlarged antibiotic gland, suggesting that this since-extinct species adjusted to underground living.

“This was an incredibly lucky find. Because this ant was probably subterranean like most army ants today, it was much less likely to come into contact with tree resin that forms such fossils,” said Sosiak. “We have a very small window into the history of life on our planet, and unusual fossils such as this provide fresh insight.”

Previously, researchers believed there were only two cases of “army ant syndrome,” in which the species would have experienced convergent evolution. These two cases occurred in Neotropics and the Afrotropics. With the latest specimen, though, there’s proof of a third.

“The discovery is the first physical evidence of the army ant syndrome in the Eocene, establishing that hallmarks of these specialized predators were in place even before the ancestors of certain army ants like Dorylus,” said Barden.

The fossil remains at the Harvard museum so that researchers can continue studying its crucial attributes.