Scorpionflies: The Oldest Known Animal Pollinators

A new study suggests that scorpionflies that lived during the Jurassic Period fed on the nectar-like juices of seed ferns, conifers, and other primitive plants. As the scorpionflies feasted on the sweet liquid from these plants, they may have also acted as animal pollinators—couriers of pollen grains that are vitally necessary to the reproductive cycle of their host plants. If this scenario is true, scorpionflies represent the earliest known animal pollinators.

In general, for plants to reproduce, pollen grains must be transported from the stamen of a flower to the pistil. There are numerous ways that this transfer can take place—pollen can be carried from stamen to pistil by the wind, water, or by animals.

Until now, scientists believed that primitive plants—plants that predated flowering plants—relied mainly on wind for pollination, not on insects. The understanding was that it animal pollination didn't become widespread until flowering plants evolved during the late Cretaceous period (99.6 to 65.5 million years ago).

But that reasoning has now been called into question by Dong Ren of Capital Normal University, Beijing, China and his colleagues. The scorpionfly fossil evidence they present suggests that scorpionflies may have been pollinating plants as early as 167 million years ago, long before animals started pollinating flowering plants during late Cretaceous.

Ren and colleagues have shown that ancient scorpionflies were equipped with elaborate, siphon-like mouthparts that would have enabled the ancient insects to extract nectar from deep within primitive plants. They also determined that there were five potential plants that the ancient scorpionflies could have visited: a conifer, seed fern, ginkgoopsid, pentoxylaean, and gnetalean. These plants all had reproductive organs that were poorly suited for wind pollination, suggesting that the plants relied instead on animal pollination.

The evidence for scorpionflies as ancient pollinators is not without its loopholes though. It turns out that Ren and colleagues looked for pollen grains in the fossils, reasoning that if scorpionflies were indeed transporting pollen, than some might have been preserved with the specimens. They found no evidence of pollen in any of the fossils they studied.

Refs:
Ren, D., Labandeira, C., Santiago-Blay, J., Rasnitsyn, A., Shih, C., Bashkuev, A., Logan, M., Hotton, C., & Dilcher, D. (2009). A Probable Pollination Mode Before Angiosperms: Eurasian, Long-Proboscid Scorpionflies Science, 326 (5954), 840-847 DOI: 10.1126/science.1178338

Ollerton J, & Coulthard E (2009). Paleontology. Evolution of animal pollination. Science (New York, N.Y.), 326 (5954), 808-9 PMID: 19892970

Related: Photos: The Oldest Known Animal Pollinators

Photos © Wenying Wu.