Glow in the Dark

99-million-year-old fossil reveals why these strange animals glow

Giphy

It's like something out of Jurassic Park. A scientist discovers an ancient insect preserved in amber, and the discovery changes the scientific world forever.

The ancient insect in question is the beetle Cretophengodes azari, found exceptionally well-preserved in Myanmar within 99-million-year-old amber. According to research published Wednesday in the journal Proceedings of the Royal Society B, the beetle is part of a newly discovered insect family from the mid-Cretaceous period.

The beetle is also shifting our understanding of the original purpose of bioluminescence. Analysis suggests the insect's light production evolved as a defense mechanism — much like modern-day fireflies (a distant relative of the ancient beetle) use light to ward off predators. Today bioluminescence is used for purposes ranging from mimicry to attracting mates, but in one of its earliest forms, it very likely kept creatures alive.

Bioluminescent background — Glowing animals have long fascinated scientists, whether they be platypuses, geckos, or beetles.

It's a phenomenon long intertwined with the history of the animal kingdom. The study states: "Bioluminescence, the production of light by living organisms, evolved over 30 times independently on diverse branches of the tree of life."

What they found — The researchers discovered an ancient bioluminescent male beetle specimen preserved in amber from Myanmar.

From that specimen, researchers discovered an entirely new Cretaceous-era beetle family: the Cretophengodidae. The specific beetle specimen also got its own new species: Cretophengodes azari. A light-producing organ on the beetle's abdomen generates its bioluminescent features.

An artist rendering of the Cretophengodes azari.Dinghua Yang

Bioluminescent beetles like Cretophengodes azari fall into the Elateroidea superfamily, which includes living insects like fireflies, fire beetles, and glow-worms. There are more than 2,000 bioluminescent beetles — far greater than any other light-producing terrestrial animal family on the planet.

Traditionally, scientists have divided the Elateroidea insect superfamily into two groups: hard-bodied elateroids and soft-bodied members of the Phengodidae and Rhagophthalmidae clades. The study's ancient beetle represents a transition between the soft-bodied insects and the hard-bodied ones, the authors suggest.

A map from the study showing the geographic location of beetles in this insect superfamily.

"The unique combination of characters in Cretophengodes is unknown in any currently defined beetle lineage," the study team writes.

Why this matters — The findings are a pair: A new understanding of bioluminescence and a discovery of life.

Because of the insect's unique features, researchers believe Cretophengodes azari is an ancient missing link, or transitional fossil, between the soft-bodied clades and the hard-bodied elateroids. The scientists believe this unique beetle is deserving of its own family.

A figure from the study showing the evolution of this new beetle.

The function of beetle bioluminescence — glowing reds and greens — has, in turn, been poorly understood prior to now.

Among bioluminescent beetles, juvenile larvae glow more often than adults. These larvae emit light regularly during the night or spontaneously when disturbed. Previous studies indicated that predators — like spiders, ants, frogs, and birds — may avoid glowing larvae.

The researchers speculate that beetles may have evolved bioluminescence primarily as a defense mechanism against predators, and only later adapted it for other purposes, such as mating.

Scientists in this study added extra weight to that hypothesis, stating that many of these predators' ancestors originated during the early-Cretaceous period, and their fossil specimens can also be traced back to Myanmar.

A figure from the study comparing the newly-discovered insect to the Rhagophthalmidae and Phengodidae families.

What's next — This new fossil finding opens up a new world of scientific understanding regarding bioluminescence.

But it's still missing one key item: a female specimen to compare to the male specimen described in the study. Yes, even beetles have a diversity problem.

Previous research indicates that female beetles, in particular, retain bioluminescent-related features into adulthood. Scientists may have been unable to identify adult female members of the Cretophengodidae family because they closely resemble juvenile larvae.

A lack of female specimens hinders our understanding of beetle bioluminescence overall. To really refine our understanding of the past, both samples are needed.

"Even in extant neotenic groups, females are much less represented in collections or are not known at all," the study team writes.

The future of bioluminescence research is female — and the hunt for those ancient specimens continues.

Abstract: Bioluminescent beetles of the superfamily Elateroidea (fireflies, fire beetles, glow-worms) are the most speciose group of terrestrial light-producing animals. The evolution of bioluminescence in elateroids is associated with unusual morphological modifications, such as soft-bodiedness and neoteny, but the fragmentary nature of the fossil record discloses little about the origin of these adaptations. We report the discovery of a new bioluminescent elateroid beetle family from the mid-Cretaceous of northern Myanmar (ca99 Ma), Cretophengodidae fam. nov. Cretophengodes azarigen. etsp. nov. belongs to the bioluminescent lampyroid clade, and would appear to represent a transitional fossil linking the soft-bodied Phengodidae + Rhagophthalmidae clade and hard-bodied elateroids. The fossil male possesses a light organ on the abdomen which presumably served a defensive function, documenting a Cretaceousradiation of bioluminescent beetles coinciding with the diversification of major insectivore groups such as frogs and stem-group birds. The discovery adds a key branch to the elateroid tree of life and sheds light on the evolution of soft-bodiedness and the historical biogeography of elateroid beetles.
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