Fossilized tree resin, or amber, from the Cretaceous period has provided all kinds of fascinating insights into long-gone creatures that once inhabited the Earth. These include ticks with an appetite for dinosaur blood, dinosaurs with feathered tails and mysterious millipedes that shake up established evolutionary timelines. Joining them is a rare 99-million-year-old fossil that shows an enigmatic haidomyrmecine “hell ant” clamping down on its cockroach-like prey.
The research was carried out by researchers from New Jersey Institute of Technology (NIJT), the Chinese Academy of Sciences and the University of Rennes in France, who describes the fossil as one of the most vivid pictures yet into how hell ants secured their food over their almost 20-million-year existence on Earth.
“Since the first hell ant was unearthed about a hundred years ago, it’s been a mystery as to why these extinct animals are so distinct from the ants we have today,” says NIJT’s Phillip Barden, lead author of the study. “This fossil reveals the mechanism behind what we might call an ‘evolutionary experiment,’ and although we see numerous such experiments in the fossil record, we often don’t have a clear picture of the evolutionary pathway that led to them.”
The reason Barden and the team see this as an "evolutionary experiment," is because of how this feeding mechanism differs from that seen in the ants of today, which feature mouth parts that move together laterally. Conversely, the hell ant, which is thought to have vanished around 65 million years ago, moves its mandibles in a vertical fashion.
This was observed in the amber fossil, where a newly identified subspecies of hell ant called Ceratomyrmex ellenbergeri can be seen using its mandibles vertically to pin its prey in place – in this case an extinct relative of the cockroach called Caputoraptor elegans. The team describes this as some of the first direct evidence of hell ants using these tusk-like features in this way.
“Fossilized behavior is exceedingly rare, predation especially so,” says Barden. “As paleontologists, we speculate about the function of ancient adaptations using available evidence, but to see an extinct predator caught in the act of capturing its prey is invaluable. This fossilized predation confirms our hypothesis for how hell ant mouthparts worked … The only way for prey to be captured in such an arrangement is for the ant mouthparts to move up and downward in a direction unlike that of all living ants and nearly all insects.”
These findings help fill in some of the blanks around the feeding habits of some of the early ant species (of which hell ants are one), and how this species sustained itself across a 20-million-year existence. The team now hopes to build on this work by investigating what causes some species to become extinct while other survive and thrive.
“Over 99 percent of all species that have ever lived have gone extinct,” says Barden. “As our planet undergoes its sixth mass extinction event, it’s important that we work to understand extinct diversity and what might allow certain lineages to persist while others drop out. I think fossil insects are a reminder that even something as ubiquitous and familiar as ants have undergone extinction.”
The research was published in the journal Current Biology.
