New fossil sheds light on early evolution of ants

NANJING - Scientists have discovered a new species of ant in a 99-million-year-old piece of Burmese amber. The bizarre-looking ant has a prominent cephalic horn and oversized, scythe-like mandibles that extend above its head.

According to Nanjing Institute of Geology and Paleontology, under the Chinese Academy of Sciences, the fossil suggests that at least some of the earliest ants were solitary specialist predators.

Ants experienced their early diversification within the Cretaceous period. The success of ants is generally attributed to their remarkable social behavior.

Recent studies suggest that the early branching lineages of extant ants formed small colonies of subterranean or epigeic, solitary specialist predators.

The vast majority of Cretaceous ants belong to the stem-group Formicidae and comprise workers and reproductives of largely generalized morphologies. Although it is difficult to draw clear conclusions about their ecology, recent discoveries from the Cretaceous suggest relatively advanced social levels.

Remarkable exceptions to this pattern are ants with bizarre mouthparts in which both female castes have modified heads and blade-like mandibles, which move uniquely in a horizontal rather than vertical plane.

Questions over the specific ecology of haidomyrmecines have puzzled evolutionary biologists for many years, as their mandibles appear to act as traps triggered by sensory hairs in a way distinct from that of modern trap-jaw ants

Not all ants cooperate in social hunting, however, and some of the most effective predatory ants are solitary hunters with powerful trap jaws. Models of early ant evolution predict that the first ants were solitary specialist predators, but discoveries of Cretaceous fossils suggest group recruitment and socially advanced behavior among stem-group ants.

Wang Bo from the Nanjing institute and his colleagues said the structures of the new ant presumably functioned as a highly-specialized trap for larger prey. The horn results from an extreme modification of the clypeus hitherto unseen among living and extinct ants, which demonstrates the presence of exaggerated trap-jaw morphogenesis early among stem-group ants.

Together with other Cretaceous haidomyrmecine ants, the new fossil suggests that at least some of the earliest Formicidae were solitary specialist predators. In addition, it demonstrates that early ant societies in the Early Cretaceous, descendant from at least one lineage -- the Haidomyrmecini, became adept at prey capture, independently arriving at morphological specializations that would be lost for millions of years after their disappearance near the close of the Mesozoic.

The new fossil reveals a proficiency for large-bodied carriage and highlights a more complex and diversified suite of ecological traits for the earliest ants, according to researchers.