Pollen eaters and pollen morphology : co-evolution through the Permian and Mesozoic

In each of the sequential periods of seed-plant evolution, there were "charismatic" pollen grains that fascinated generations of palynologists. In the Permian, such peculiar pollen morphologies included taeniate pollen (with the wall split into bands, or taeniae) of Protohaploxypinus-Lunatisporites and Vittatina groups. One or more types of taeniate pollen prevailed in the pollen load of several species of Permian insects. The advent of the Mesozoic era was marked by a spread of smooth asaccate pollen of "Ginkgocycadophytus" type, virtually indistinguishable in the dominant orders of Mesozoic gymnosperms. Such pollen was never found in the guts. Charismatic through the Mesozoic was the rimulate pollen of Classopollis type. It constituted a monospecific load in the guts of large Jurassic katydids (Aboilus, Haglidae). The Eucommiidites group, related to gnetophytes, is peculiar in having lateral grooves parallel to the main sulcus. Recently this pollen type has been found in the gut compression of a xyelid, genus Ceroxyela. The reason why Palaeozoic and Mesozoic insects showed preferences for pollen with distinctive morphologies might be that, on the basis of the surface ornamentation of these different varieties, insects were able to distinguish edible pollen types. The distinctive pollen morphologies might have evolved primarily for this purpose.