Discovery of 'Jurassic butterflies'

An image of the fossilized lacewing Oregramma illecebrosa (left) and the modern owl butterfly Caligo Memnon (right).
Credit: Conrad C. Labandeira and Jorge Santiago-Blay.

IU paleobotanist David Dilcher is a co-author on a study out today in the Proceedings of the Royal Society: B that identifies a Jurassic age insect whose behavior and appearance closely mimic a butterfly -- but whose emergence on Earth predates the butterfly by about 40 million years.

Dilcher -- who made international headlines last year for his role in discovering the mythical "first flower" -- said these proverbial "first butterflies" survived in a similar manner as their modern sister insects by visiting plants with "flower-like" reproductive organs producing nectar and pollen.

The butterfly-like insects, which went on to evolve into a different form of insect from the modern butterfly, is an extinct "lacewing" of the genus kalligrammatid called Oregramma illecebrosa. Another genus of this insect -- of the order Neuroptera -- survives into our modern era, and are commonly known as fishflies, owlflies or snakeflies.

The discovery of the insect was made possible by the examination of well-preserved fossils recently recovered from ancient lake deposits in northeastern China and eastern Kazakhstan. The study was led by Conrad Labandeira, a curator at the Smithsonian Institution's National Museum of Natural History, and Dong Ren of Capital Normal University in Beijing, China, where the fossils are housed.

"Poor preservation of lacewing fossils had always stymied attempts to conduct a detailed morphological and ecological examination of the kalligrammatid," Dilcher said. "Upon examining these new fossils, however, we've unraveled a surprisingly wide array of physical and ecological similarities between the fossil species and modern butterflies, which shared a common ancestor 320 million years ago. "

The species are an example of convergent evolution, Dilcher explains, where two distantly related animals develop similar characteristics independently.

As a paleobotanist, Dilcher contributed to the study by describing these ecological similarities, including the insect's relationship to a type of fossilized plant found in the same region of China as the insect fossils. An extinct order of seed plants called bennettitales, these plants first appeared about 250 million years ago during the Triassic period, surviving for nearly 200 million years until the end of the late Cretaceous period.

Based on their examination, which drew in part upon microscopically small clues such as the fossilized remains of food and pollen trapped in the mouthparts of the insects, Dilcher and colleagues concluded kalligrammatid fed upon bennettitales using a long tongue to probe nectar deep within the plant. The insects also possessed hairy legs that allowed for carrying pollen from the male flower-like reproductive organs of one plant to the flower-like female reproductive organs of another.

Eventually, this system of pollination by long-tongued lacewings traveling between plants with exposed reproductive parts -- called gymnosperms -- gave way to more familiar system of insect pollinators and modern flowers, or angiosperms, in which the reproductive parts of the plants are contained with a protective seed.

However, another evolutionary innovation found in the ancient lacewing fossils' wings remained remarkably unchanged over the course of millennia: so-called "eye spots."

This unique pattern on the wings, arising over 200 million years ago, is nearly identical to markings on the modern owl butterfly. To this day, owl butterflies use these circular marks as a defense mechanism against predators, which mistake the spots as the eyes of a larger, more threatening animal.

Evolution is a great innovator, Dilcher said. But at the same time: "if it worked once, why not try it again."

This work was supported in part by the National Basic Research Program of China, National Science Foundation of China, National Institutes of Health and Swedish National Space Board.