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Oldest Army Ant Ever Discovered Reveals Legendary Predator That Once Invaded Europe


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NEWARK, NJ, Nov. 22, 2022 (GLOBE NEWSWIRE) — Their nomadic lifestyle and predation have brought army ants (Dorylinae) to most of Earth’s continents, but a rare fossil discovery is now providing the first evidence that the notorious predators once swarmed a country where they are conspicuously absent today – Europe.

In the newspaper biology lettersResearchers from the New Jersey Institute of Technology and Colorado State University have reported the discovery of the oldest army ant preserved in Eocene (about 35 million years ago) Baltic amber.

The eyeless specimen Dissimulodorylus perseus (D. pers)named after the mythical Greek hero Perseus, who famously defeated Medusa with impaired vision – is only the second army ant fossil species ever described and the first army ant fossil recovered from the Eastern Hemisphere.

Researchers say the ant fossil, about 3 millimeters long, brings to light previously unknown lineages of army ants that would have existed across continental Europe before going extinct in the last 50 million years.

Remarkably, the fossil was kept hidden in Harvard University’s Museum of Comparative Zoology for almost 100 years before being identified by the publication’s lead author and NJIT graduate student Christine Sosiak.

“The museum houses hundreds of drawers full of insect fossils, but while collecting data for another project, I happened to come across a tiny specimen that was labeled as a common ant species,” Sosiak said. “When I put the ant under the microscope, I immediately realized the label was inaccurate… I thought that’s something else entirely.”

“This amber was excavated around or before the 1930s, So it’s surprising enough to learn now that it contained a rare army ant, let alone one that shows these ants roamed Europe,” said Phillip Barden, assistant professor of biology at NJIT and senior author of the paper. “From what we know of army ants alive today, there is no evidence of such an extinct variety. … With this fossil now vanished from obscurity, we have gained a rare paleontological porthole into the history of these unique predators.”

A paleontological porthole into the history of a unique predator

Today, about 270 army ant species live in the Eastern Hemisphere and about 150 in North and South America.

Based on X-ray and CT scan analyzes of the fossil, the NJIT team collected phylogenetic and morphological data on these locations D. pers as a close relative of eyeless species of army ants currently found in Africa and southern Asia dorylus.

“By the time the fossil formed, Europa was hotter and wetter than it is today and may have provided an ideal habitat for ancient army ants,” Barden said. “However, Europa has undergone multiple cooling cycles spanning tens of millions of years since the Eocene, which may have been inhospitable to these tropically adapted species.”

The team’s analysis also revealed that the ant possessed an enlarged antibiotic gland, typically found in other army ants, to sustain underground life, suggesting that the long-lost lineage of European army ants was similarly suited to underground living .

It’s a factor that makes this fossil, and other fossil army ants, a rarity, according to Sosiak. So far, only a single definitive fossil has been recorded unearthed in the Caribbean (~Ma. 16).

“It was an incredibly lucky find. Because this ant probably lived underground like most modern-day army ants, it was much less likely to come in contact with tree sap that forms such fossils,” Sosiak said. “We have a very small window into the history of life on our planet, and unusual fossils like this offer new insights.”

says Sosiak D.perseus’ Anatomical features — including its tapered mandibles and lack of eyes — help classify the specimen as a worker ant in its colony, which would have carried its queen’s larvae and foraged with soldier ants had it been alive.

“Army ant workers engage in raids on swarms, preying on other insects and even vertebrates. Because these army ants are blind, they use chemical communication to stay coordinated with each other and take down large prey,” Sosiak explained. “This worker may have strayed too far from its fellow hunters and got caught in sticky tree sap, which eventually solidified and encased the ant as we see it today.”

The distinct combination of army ant behavior and traits is so unusual in the ant world that it deserves its own name – army ant syndrome.

Unlike other ant lineages, army ants have wingless queens that can lay millions of eggs per day, while between migratory stages their nomadic colonies temporarily occupy nests that take the form of bivouacs, sometimes containing millions of ants, stretching over 100 m.

The carnivores are perhaps best known for their highly coordinated foraging, which can consume up to 500,000 prey items per day.

Barden says the Army Ant Syndrome is a case of convergent evolution that happened twice – once in the Neotropics and once in the Afrotropics.

“The discovery is the first physical evidence of Eocene army ant syndrome, demonstrating that characteristics of these specialized predators predate the ancestors of certain army ants dorylus‘ said Barden.

For the time being, the newly identified fossil joins only eight fossil species within the ant subfamily to which army ants belong, called Dorylinae – five from Dominican amber (16 ~Ma.) and three species from Baltic amber (34 ~Ma. ) are known.

D. pers deposited for future study in the Museum of Comparative Zoology at Harvard University.

….

Sosiak CE, Borowiec ML, Barden P. 2022 An Eocene Army Ant. Biol. Lette.

https://doi.org/10.1098/rsbl.2022.0398

  • Army Ant in Amber

  • Army Ant Reconstruction

Deric Raymond
New Jersey Institute of Technology
9736247042
[email protected]

Source: New Jersey Institute of Technology


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