100 million-year-old amber points to oldest animal societies

Fighting ants, giant soldier termites and foraging worker ants recently discovered in 100-million-year-old amber pieces from Myanmar provide direct evidence of advanced social behaviour in ancient ants and termites, say researchers.

Advanced sociality, or eusociality, a hallmark of which is reproductive specialisation into worker and queen castes, is essentially a phenomenon of the group of invertebrates known as arthropods.

However, before the new work, the earliest termites ever found that could definitively be tied to a caste system were from the Miocene epoch, a mere 17 to 20 million years ago.

"In the Cretaceous amber we examine, the ants and termites represent the earliest branches of each evolutionary tree, and the species are wildly different from what their modern relatives look like today," said study co-author Phillip Barden from Rutgers University in New Jersey, US.

The new work, led by scientists at the American Museum of Natural History and the University of Kansas, was published in two papers in the journal Current Biology.

"We wanted to know how social these creatures were, if they were social at all," Barden noted.

A number of spectacular pieces of amber recently recovered from Myanmar gave Barden and colleagues a clear answer: Eusociality was going strong in both groups - ants and termites during the Cretaceous period.

In termites, the researchers made this determination based on the diverse anatomy of the animals, indicating the presence of castes.

The amber ant fossils froze a number of eusocial behaviours in time. Those include the presence of different castes, including queen ants and workers; groups of worker ants in single pieces of amber, probably nestmates foraging together; and two workers of different ant species engaging in combat, the researchers said.