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Scythe-jawed hell ant from 113 million years ago is oldest known specimen

A 113-million-year-old hell ant that once lived in northeastern Brazil is now the oldest ant specimen known to science, finds a report in Current Biology. The hell ant, which was preserved in limestone, is a member of Haidomyrmecinae—an extinct subfamily that only lived during the Cretaceous period. These ants had highly specialized, scythe-like jaws that they likely used to pin or impale prey.

"Our team has discovered a new fossil ant species representing the earliest undisputable geological record of ants," said author Anderson Lepeco of Museu de Zoologia da Universidade de São Paulo in Brazil.

"What makes this discovery particularly interesting is that it belongs to the extinct 'hell ant,' known for their bizarre predatory adaptations. Despite being part of an ancient lineage, this species already displayed highly specialized anatomical features, suggesting unique hunting behaviors."

The ant fossil's discovery challenges our understanding of ant evolution and biogeography through time, according to the researchers. The previous oldest ants were found in France and Burma and were preserved in amber instead of limestone. The existence of a hell ant in Brazil shows that ants were already widely distributed and diversified early in their evolution, says the team.

"Even though there have been hell ants described from amber, this was the first time we could visualize this in a rock fossil," said Lepeco.

Lepeco and his team discovered the "remarkably well-preserved" ant specimen while systematically examining one of the world's largest collections of fossil insects from the Crato Formation, a deposit renowned for its exceptional fossil preservation. The collection is housed at the Museu de Zoologia da Universidade de São Paulo.

"When I encountered this extraordinary specimen, we immediately recognized its significance, not only as a new species but as potentially the definitive evidence of ants in the Crato Formation," said Lepeco.

"This finding highlights the importance of thorough examination of existing collections—private or in museums—and brings a spotlight to Brazilian paleontology and the underexplored fossil insect fauna of the country."

Micro-computed tomography imaging—a 3D imaging technique that uses X-rays to view the inside of an object, or ant in this case—showed that the newly discovered ant was closely related to hell ants previously known only from specimens preserved in Burmese amber—a type of amber found in Myanmar.

The finding shows that the ants were widely distributed across the globe and must have crossed Cretaceous landmasses repeatedly, say the authors. But what astonished them most was the hell ant's specialized features.

"While we expected to find hell ant features, we were shocked by the characteristics of its feeding apparatus," said Lepeco.

Unlike modern ants with laterally moving mandibles, this species possessed mandibles that ran forward parallel to the head and facial projection anterior to the eyes, the researchers noted.

"Finding such an anatomically specialized ant from 113 million years ago challenges our assumptions about how quickly these insects developed complex adaptations. The intricate morphology suggests that even these earliest ants had already evolved sophisticated predatory strategies significantly different from their modern counterparts."

The discovery of this new ant specimen raises broader questions about the evolutionary pressures that led to the hell ant's unique adaptations, say the researchers. With advanced imaging tools, it's now possible to examine such fossil specimens in much greater detail than ever before.