GYMNOSPERMS, ANGIOSPERMS AND INSECT POLLINATORS TRANSITING THE ALBIAN-APTIAN GAP

A fundamental ecological event of the Mesozoic was the worldwide shift from a gymnosperm to an angiosperm-dominated world during the Barremian to Cenomanian Stages of the Cretaceous. The overwhelming brunt of this transition occurred during the 35 million-year-long Aptian–Albian Gap, resulting in major changes of four, well-documented pollination modes. Pollination Mode 1 consisted of thrips bearing mouthcone mouthparts, engaged in punch-and-sucking feeding, and pollinating a ginkgoalean host that bore Cycadopites pollen. Pollination Mode 2 was a beetle with mandibulate mouthparts, engaged in a chewing feeding style, and pollinating a cycad host bearing Monosulcites pollen. Pollination Mode 3 was a very diverse guild of 41 species of Neuroptera (lacewings), Mecoptera (scorpionflies), Diptera (true flies) and Lepidoptera (moths), representing 13 to 15 separate evolutionary originations of long-proboscid mouthparts, engaged in a siphoning feeding style, and pollinating cheirolepidiaceous conifers based on Classopollis pollen and bennettitaleans based on Exesipollenites pollen. Pollination Mode 4 consisted of true flies with labellate mouthparts, a sponging feeding style, and pollinating a cheirolepidiaceous conifer with Classopollis pollen.

These four pollination modes collectively had four separate fates across the Aptian–Albian Gap, each composed of a distinct evolutionary-ecological cohort of pollinators responding to the effects of gymnosperm-to-angiosperm turnover. First, were gymnosperm pollinating lineages, such as a zhangsolvid long-proboscid fly on a bennettitalean that became extinct and thus failed the transition onto angiosperms. Second, were gymnosperm-pollinating lineages, such as a merothripid thrips on a ginkgoalean that survived on gymnosperms but in substantially decreased diversity. Third, were gymnosperm-pollinating lineages, such as an oedemerid beetle on a cycad that successfully made the transition onto angiosperms. Fourth, were newly evolved pollinator lineages, such as bees that originated with angiosperms but never had gymnosperm hosts in their history. The direct evidence of pollinator–seed plant associational data should be corroborated with analogous insect herbivore–seed plant data by using damage-type studies across the Aptian–Albian Gap.