Did beetles visit Pseudanthus (Picrodendraceae) flowers in the Eocene of Europe?

During ongoing investigations of flower-insect interactions in the Eocene of Central Europe we discovered two different beetles, a Scarabaeidae (scarab) and Cerambycidae (longhorn) beetle from the Middle Eocene of Messel (Germany), with their bellies full of the same peculiar pollen type. In light microscopy (LM), the pollen grains are small, spherical, echinate, and pantoporate. Additional studies applying scanning- (SEM) and transmission electron microscopy (TEM) how that the extracted pollen is also perforate in SEM, and with a complex, structured sporopollenin pollen wall in TEM. Based on the combined morphological and ultrastructural features observed with LM/SEM/TEM, the fossil pollen is comparable to pollen of extant Pseudanthus. Today, Pseudanthus (Picrodendraceae) comprises eight to nine species that are all endemic to the subtropical, seasonally dry tropical, or dry tropical biomes of East Australia. The plants are small subshrubs or shrubs and monoecious. Pseudanthus grows on sandy soils, sandstones and rocks (often of volcanic origin) in various habitats that include open forests and woodlands, shrublands, heathland, rainforests (rarely), gorges, along creek banks, in crevices, on hillsides, cliff faces, and mountain tops. Pseudanthus are considered entomophilous, but little is known about their insect visitors and main pollinators. Our findings prove that both scarab and longhorn beetles visited Pseudanthus flowers in the Middle Eocene of Europe to feast on pollen. The plants were likely growing on sandy or rocky volcanic substrate in the vicinity of the Messel lake maar. The amount of pollen filling the guts of the beetles and the adhered pollen discovered on their exterior suggest long and careful feeding visits within the male flowers. To prove that the beetles also visited/came into contact with female flowers is unrealistic, but if they did, the amount of pollen discovered supports the theory that they were true pollinators of Pseudanthus back in the Eocene of Europe.