A close-up view of the well-preserved Cretophengodes azari, a fossil light-producing beetle encased in amber.

A beetle trapped in amber for over 100 million years is offering scientists clues to why the bioluminescent insects may have glowed way back during the Cretaceous period, about 145 to 66 million years ago. .

In a new study published in the journal Proceedings of the Royal Society B, scientists reveal that a Cretophengodes beetle found "preserved with life-like fidelity in amber" has a direct connection to its firefly cousins. .