Jason Shih
Two modern-day froghoppers in a mating embrace.
About 165 million years ago, in what is now northeastern China, two insects were doing what comes naturally. Suddenly, in the middle of copulating, they were struck dead, felled by poisonous gas from a volcanic eruption.
But the moment was not lost. Fortunately for science, the insects, still in the grip of what passes for passion among froghoppers, sank to the bottom of a lake where they were preserved for the ages under layers of ash and sediment.
They ended up in an insect fossil collection in Beijing, and scientists poring over the collection recently discovered and exposed them.
The scientists, Shu Li and Dong Ren, of Capital Normal University, and colleagues there and at other universities reported Wednesday in the journal PLoS One that the exquisitely detailed preservation is the oldest fossil of two insects copulating.
In a clear act of sentiment, the researchers titled their paper, "Forever Love: The Hitherto Earliest Record of Copulating Insects from the Middle Jurassic of China." But the discovery is scientifically significant because the mating behavior exhibited is essentially the same as that of froghoppers today.
Fossils that show behavior of any sort are unusual, and fossils of mating insects even more so.
"This one is so rare," said Chungkun Shih, a visiting professor at the university and one of the authors of the paper. "I got involved in this research in 1999, and I have seen more than half a million fossils," but this was the only one in which the insects were clearly mating.
Only 33 examples of copulating insects are known to exist in the entire fossil record, most of them caught in amber. Until now, the oldest was two tiny flies, what fly fishers call midges, preserved in 135 million-year-old amber from Lebanon.
George O. Poinar Jr., a paleoentomologist at Oregon State University, who wrote about those flies, said he did not know of any other fossil of froghoppers copulating, probably because "they're so big they don't stick in amber."
The froghoppers are part of a treasure trove of creatures killed in the volcanic eruption, including feathered dinosaurs, all somehow ending up in the lake. The froghoppers were mating "belly to belly," the scientists reported, although they may have been pressed into that position by the weight of sediment during fossilization.
Dr. Shih, a retired chemical engineer and businessman who found a second career working with the fossil insect group at Capital Normal University and now lives in New Jersey, said that modern froghoppers mate side by side or belly to belly, depending on whether they are on a flat surface or clinging to a vertical stem.
Marlene Zuk, an evolutionary biologist at the University of Minnesota and author of "Sex on Six Legs: Lessons on Life, Love and Language From the Insect World," said that by and large, "behavior doesn't fossilize," so it is rare to have it preserved so clearly.
"Obviously," she said, "there's behavior going on here."
As to why the froghoppers' behavior has remained essentially the same for 165 million years, the authors did not comment in the paper. But Dr. Shih said he thought the explanation was probably simple. "This works," he said. "They don't need to change."
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