A 35 million-year-old Baltic amber block containing the world's oldest army ant was discovered by researchers at the New Jersey Institute of Technology and Colorado State University.
The unexpected finding shows that the aggressive, blind insects, which are currently widespread in Africa and South America, once traversed Europe.
“We didn’t think they were in Europe,” says Christine Sosiak at the New Jersey Institute of Technology. “It’s actually completely unheard of to find them there. And yet here we have this [European] army ant, from so far back in history!”
Sosiak was looking through fossilized amber-embedded ant specimens that had been kept at Harvard University since the 1930s when she came across one that appeared to have been incorrectly classified as a member of the widespread Platythyrea genus.
“The museum houses hundreds of drawers full of insect fossils, but I happened to come across a tiny specimen labeled as a common type of ant while gathering data for another project,” said Sosiak. “Once I put the ant under the microscope, I immediately realized the label was inaccurate … I thought, this is something really different.”
“This amber would have been excavated around or before the 1930s, so to now learn it contained a rare army ant is surprising enough, much less one that demonstrates these ants roamed Europe,” said Phillip Barden, assistant professor of biology at NJIT and senior author of the paper. “From everything we know about army ants living today, there’s no hint of such extinct diversity. With this fossil now out of obscurity, we’ve gained a rare paleontological porthole into the history of these unique predators.”
Sosiak and her coworkers captured high-resolution photos and a 3D model of the lustrous, well-preserved brown ant, using photography and microscopic CT scans. They realized that, unlike most ant species, this insect lacked eyes and possessed jaws with sharp points, a single waist segment, and a sizable gland that would have released protective substances essential for subterranean life.
Although surprising, the discovery of the Baltic army ant makes sense, given that Europe was warmer and wetter throughout the insect's existence, according to Sosiak.
The research team gave the ant the name Dissimulodorylus Perseus in honor of the Greek mythological figure Perseus, who defeated Medusa without being able to see her. The name is derived from the Latin term dissimulo, which means to conceal or hide.
This discovery will shine a light on the evolution of ants, and the places different ant species have been.
Study Abstract:
Among social insects, army ants are exceptional in their voracious coordinated predation, nomadic life history and highly specialized wingless queens: the synthesis of these remarkable traits is referred to as the army ant syndrome. Despite molecular evidence that the army ant syndrome evolved twice during the mid-Cenozoic, once in the Neotropics and once in the Afrotropics, fossil army ants are markedly scarce, comprising a single known species from the Caribbean 16 Ma. Here we report the oldest army ant fossil and the first from the Eastern Hemisphere (EH), Dissimulodorylus perseus, preserved in Baltic amber dated to the Eocene. Using a combined morphological and molecular ultra conserved elements dataset spanning doryline lineages, we find that D. perseus is nested among extant EH army ants with affinities to Dorylus. Army ants are characterized by limited extant diversification throughout most of the Cenozoic; the discovery of D. perseus suggests an unexpected diversity of now-extinct army ant lineages in the Cenozoic, some of which were present in Continental Europe.
