Amber fossil reveals hunting prowess of ancient 'hell ant'

Aug. 6 (UPI) -- An ancient amber fossil has offered scientists new insights into the deadly hunting prowess of the "hell ant" species Ceratomyrmex ellenbergeri.

The 99-million-year-old amber, unearthed in Myanmar, trapped a member of the Haidomyrmecine subfamily -- the group known as hell ants -- just as the predator snatched a cockroach relative with its scythe-like mandibles.

Animal behavior rarely becomes fossilized, and fossilized hunting behavior is especially elusive. The hell ant fossil, described Thursday in the journal Current Biology, is a one-of-a-kind find.

"Insects caught in resin tend to move around in an attempt to escape, and flowing resin can shift remains around," lead study author Phillip Barden told UPI.

"Add to this the potential for decomposition or distortion over millions of years and it's not often that you find organisms caught doing exactly what they were 100 million years ago," said Barden, an assistant professor of biological sciences at the New Jersey Institute of Technology.

Scientists knew from previously unearthed amber fossils that hell ants featured unusual mouthparts and horns, but researchers couldn't be certain how these ants used their unique mandibles and appendages.

The new fossil suggests hell ants moved their scythe-like mandibles in a vertical motion to trap their prey against their horns.

"Once the jaw begins to move vertically, it creates an evolutionary pathway for the head and jaws to evolve in concert in a way that we don't see today," Barden said. "Put another way, hell ants 'bite' the same way humans and other vertebrates do, by moving their jaws against their own head."

Hell ants emerged prior to the last common ancestor of all modern ant species. When the prehistoric ant group disappeared -- scientists estimate the last of the hell ants died out at the end of the Cretaceous -- so did their unusual mandible physiology. Today, all ants and insects utilize mouthparts that move horizontally.

Researchers suggest this vertical biting strategy is essential to the evolution and diversification of the Haidomyrmecine subfamily.

"We suspect that this innovation in jaw movement -- vertical instead of horizontal -- provided new evolutionary access to a suite of bizarre adaptations," Barden said.

"Once two anatomical features interact for the first time, there is new selective pressure for the two to evolve in concert," he said. "We suspect that the diversity of hell ant horns and jaws we see is a reflection of specialization for different prey or feeding modes, not unlike Darwin's features."

While the new fossil offered scientists fresh insights into the evolution of hell ants and their unusual morphology, researchers still aren't sure how and why they disappeared.

"An outstanding question is why hell ants and other early ant groups died out while other lineages went on to persist until the present," Barden said. "The last time we see hell ants and other early ant lineages is before the K-Pg extinction event 65 million years ago."

Researchers hope future studies well determine whether the K-Pg extinction also wiped out the last of the hell ants.