Insect Pollination of Plants May Date Back to the Permian

演化之聲
Mar 10
3 min read

Reconstruction of Tillyardembia（感謝A. Atuchin提供） — Reconstruction of *Tillyardembia*（感謝A. Atuchin提供）

The prevailing view has long held that flowering plants (angiosperms) first appeared between the Jurassic and early Cretaceous periods, with some researchers proposing an even earlier origin. Consequently, insect-mediated pollination has traditionally been regarded as an ecological interaction that emerged only after the rise of angiosperms. However, fossil discoveries in recent years suggest that such mutualistic relationships may already have existed among gymnosperms during the Permian period.

In the past, most evidence for insect pollination in the Paleozoic and Mesozoic eras was inferred indirectly. Paleontologists relied on clues such as the morphology of plant cones or flowers that appeared suitable for insect visitation, or the presence of elongated mouthparts in insects that might have been adapted for feeding on nectar. Direct evidence—such as fossil insects bearing pollen grains on their bodies—has primarily been recovered from Cretaceous amber deposits. Earlier examples are extremely rare. When insects are preserved in sedimentary rocks, the depositional environment may have involved water transport or abrasion that removed pollen originally attached to the body surface. As a result, reconstructing the early evolutionary history of insect pollination from such fossils is particularly challenging. Only a few cases have been reported, including Jurassic lacewings of the family Kalligrammatidae and some early Cretaceous brachyceran flies preserved in sedimentary rocks that retain traces of pollen.

A Permian fossil Lagerstätte from the Chekarda locality in Russia has provided new insights into this issue. The site has yielded fossils representing more than two hundred insect species. Among them, insects of the polyneopteran genus Tillyardembia were especially abundant during the Permian. These insects measured about 1.5 cm in length and possessed wings that appear to have been poorly suited for sustained flight, suggesting that they likely spent much of their time crawling on the ground or on plant surfaces.

Researchers reexamined 425 specimens of Tillyardembia housed at the Borissiak Paleontological Institute and discovered that six individuals preserved pollen grains on their thorax or abdomen. In addition, pollen remains were identified within the digestive tract of some specimens, indicating that these insects consumed pollen as part of their diet. The dorsal plates of the abdomen bear short hairs, structures that would have facilitated the adherence of pollen grains.

Analysis of the pollen types suggests that these insects exhibited a preference for particular plants. The pollen grains were identified as belonging to three genera—Cladaitina, Luberisaccites, and Striatites—which are associated with coniferous plants belonging to the Rufloriaceae. These plants ranged from the Carboniferous to the Triassic and represent a lineage of early conifers. Although Rufloriacean plants were not the dominant vegetation in the region, Tillyardembia appears to have been particularly associated with them, possibly because their pollen offered higher nutritional value.

Tillyardembia had relatively short legs and a spindle-shaped body, suggesting a lifestyle spent largely beneath stones, within decaying wood, or among leaf litter—habitats comparable to those occupied today by earwigs or rove beetles. Such an ecology contrasts sharply with the common image of pollinating insects. Nevertheless, the insect's body form would also have been well suited for climbing within the reproductive cones of gymnosperms while searching for sugary secretions. In Rufloriacean plants, the female cones were approximately 5 cm long and about 2 cm wide, whereas male cones were shorter, measuring roughly 1.5–2 cm in length. The larger female cones could have provided shelter for Tillyardembia. After feeding on nectar and pollen from the male cones, these insects might have moved to female cones for feeding or refuge, inadvertently transferring pollen (microspores) in the process.

Modern stoneflies (order Plecoptera), which form the sister group to Tillyardembia, share a broadly similar appearance. Some stoneflies feed on nectar and pollen along riverbanks and may incidentally transfer pollen during feeding. They are also relatively weak fliers. These modern insects therefore offer a possible ecological analogy for understanding the behavior of Tillyardembia. Although the presence of pollen on these Permian insects indicates that they were capable of carrying pollen, only six of the 425 examined specimens exhibited such evidence. Consequently, the overall contribution of Tillyardembia to pollination remains uncertain. Their role may have resembled that of certain modern flies that consume nectar or pollen yet contribute little to actual pollen transfer. To better understand the ecological relationship between Tillyardembia and Rufloriacean plants, further research will be necessary to determine whether specialized adaptations existed on both sides of this interaction.