Ancient ‘hell ants’ had deadly scythe-like mandibles that they used in a vertical motion to pin prey against their horn-like appendages, a fossil has revealed.
The 99 million-year old insect stunningly preserved in amber from Myanmar was trapped just as it embraced its final victim — an ancient relative of the cockroach.
Alongside revealing just how prehistoric hell ants used their mandibles, the specimen is also helping experts discern how the killer features first evolved.
There are 16 known species of hell-ants — including one dubbed Linguamyrmex vladi, after the 15th Century Romanian ruler Vlad the Impaler, which was formerly named by entomologist Phillip Barden and colleagues in 2017.
According to Dr Barden, the hell ants’ fearsome, integrated head and mouth weaponry — which allowed them to clamp their prey in their grasp — would have first evolved from the ability to move their mouthparts vertically.
This, in turn, would have allowed the mouthparts and the ants’ heads to work together in a way that is unique to this now-extinct lineage.
‘Integration is a powerful shaping force in evolutionary biology,’ said Dr Barden, who works at the New Jersey Institute of Technology.
‘When anatomical parts function together for the first time, this opens up new evolutionary trajectories as the two features evolve in concert,’ he added.
‘The consequences of this innovation in mouthpart movement with the hell ants are remarkable.’
‘Vlad’, in particular, had a nasty form of attack — with the team believing that it used a metal-reinforced horn on it head to impale prey, an ability which may have been used to feed on the internal liquids of other insects.
‘While no modern ants have horns of any kind, some species of hell ant possess horns coated with serrated teeth,’ Dr Barden added.
‘Others, like Vlad, are suspected to have reinforced its horn with metal to prevent its own bite from impaling itself.’
According to the researchers, the discovery of the new fossil demonstrating the hell ant’s feeding mode helps to explain the ancient insect’s unusual morphology.
Furthermore, the find highlights a key difference between modern ants — whose mouthparts all grasp from side-to-side — and some of their earliest relatives.
As with many other early ant lineages, the hell ants are believed to have become extinct around 65 million years ago during a period of ecological change.
‘Fossilised behaviour is exceedingly rare, predation especially so,’ said Dr Barden.
‘As palaeontologists, 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 fossilised predation confirms our hypothesis for how hell ant mouthparts worked,’ he continued.
‘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.’
The new specimen could finally clear up why hell ants are so different from their modern-day counterparts — a mystery which has puzzles biologists and palaeontologists ever since the first hell ant was found around a century ago.
‘This fossil reveals the mechanism behind what we might call an “evolutionary experiment”,’ explained Dr Barden.
‘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.’
To explore further, the researchers compared the heads and mouthparts of hell ants with those of other fossil and living ant species — alongside reconstructing the evolutionary relationships between them all.
The team concluded that the hell ants belong to one of the earliest branches of the ant evolutionary tree — and that they have a unique configuration of integrated head and mandible weaponry.
The new find has finally provided Dr Barden and colleagues with answers as to how this long-lost class of deadly ants reigned for nearly 20 million years.
However, questions still remain — such as exactly why these and other lineages went extinct while modern ants flourished.
With their initial study complete, the team is now looking to describe other ants from new fossil deposits to learn more about how extinction impacts groups differently.
‘Over 99 per cent of all species that have ever lived have gone extinct,’ Dr Barden commented.
‘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 full findings of the study were published in the journal Current Biology.