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When dinosaurs roamed Earth, their surroundings looked very different than the world of today. But there were also some similarities. And now scientists have confirmed a new one: Diverse firefly species lit up the night during the late Mesozoic.
The discovery comes from a fossil of an ancient firefly species that was initially discovered in 2016, trapped in 99 million-year-old Burmese amber from northern Myanmar. The beetle is only the second firefly species from the Mesozoic to be identified.
Scientists estimated that fireflies evolved aerial bioluminescence, the ability to glow during flight, at least 100 million years ago in a July 2022 study that analyzed the first Mesozoic firefly fossil that was described in 2015. But because firefly remains from this period can be difficult to come by since the insects' softer bodies don't preserve well in the fossil record, the evolution of the beetles and their bioluminescence has been difficult to pinpoint, experts say.
The recently identified species, dubbed Flammarionella hehaikuni, could help researchers better understand the early evolution of fireflies and this characteristic trait, according to a study published Sept. 11 in the journal Proceedings of the Royal Society B: Biological Sciences.
"The fossil helps bridge gaps in understanding the evolutionary history of the lampyroid beetles (the beetle family fireflies belong to) and shows that key traits, like abdominal light organs, have remained consistent since the mid-Cretaceous," said lead study author Chenyang Cai, professor at Nanjing Institute of Geology and Palaeontology at the Chinese Academy of Sciences in Beijing.
"How cool is it that dinosaurs once saw fireflies flying at dusk?"
Fireflies in the land of dinosaurs
Upon first look of the firefly fossil in 2016, Cai said he thought the insect was a type of beetle in the Elateroidea family — similar to a separate species Cai also helped to identify from Burmese amber in 2021 — due to the fossilized insect's unique serrate antennae that modern fireflies do not have. But when he revisited the peculiar fossil described in the new study in late 2022, Cai noticed the well-preserved light organ, a characteristic of fireflies.
How cool is it that dinosaurs once saw fireflies flying at dusk?
–Chenyang Cai, professor at Nanjing Institute of Geology and Palaeontology
There are 10 past firefly species that are only known from fossils, said Dr. Oliver Keller, a research museum collection specialist at the University of Michigan in Ann Arbor who has studied the systematics and taxonomy of fireflies.
"The significance of this discovery is in the rarity of fossils of fireflies from that period," Keller said via email. Because only one other Cretaceous firefly species has been identified, "this new species can be used to revisit the (July 2022 study) to better date the evolution of fireflies given the new evidence," he added. Keller was not part of the new study or the 2022 research.
Fireflies glow for a multitude of reasons, most commonly as a defense mechanism and a way to communicate and attract mates. While it is hard to speculate how the flashes would have looked 100 million years ago, it is possible they would have looked similar to those seen today, Keller said.
The study authors named the beetle as a homage to French astronomer Camille Flammarion and Haikun He, an amateur collector who had donated several other amber specimens to the authors, according to the study.
Firefly diversity
There are more than 2,000 firefly species found today, according to the Natural History Museum in London. The study authors hypothesize that the newly reported ancient firefly species belonged to the Luciolinae, a subfamily that currently includes about 450 species, due to the placement of the light organ on the insect's abdomen, said study coauthor Dr. Robin Kundrata, an entomologist and an associate professor in the department of zoology at the Palacký University Olomouc in the Czech Republic.
However, no existing Luciolinae species sports the peculiar antennae that the fossil had, which the authors suspect would also differ depending on the sex of the insect, according to the study. The newly identified fossil is that of a female.
What's more, the firefly fossil, which measures less than 1 centimeter long, is morphologically different from the other specimen identified in 2015, showing that the light organs of Mesozoic species were more diverse than once thought but still similar to ones in modern fireflies, Kundrata said.
The authors said they hope more firefly fossils from the Mesozoic will come to light to further scientists' understanding of the mysterious origins of the bioluminescent beetles.
"Based on the recent knowledge, fireflies originated in the Mesozoic Era although the more precise period of their origin remains unclear. … Future discoveries may reveal further information on their diversity and morphology," Kundrata said. "Since there is no information about the immature stages of fireflies from their early evolution, we would be happy for discoveries of fossil larval specimens from Mesozoic."
