GYMNOSPERM POLLEN AS A RESOURCE FOR TERRESTRIAL ARTHROPODS: THE LATE PALEOZOIC AND PRESENT COMPARED

Gymnosperm pollen from cordaitean trees (Florinites) is a common component of ancient permineralized peat. Florinites pollen occurs dispersed in the peat matrix, and undispersed in pollen cones, usually as single grains clinging to cone scales, rarely in pollen sacs, and also in coprolites and fecal pellets. Pollen-filled coprolites found in cordaitean peat are generally 200-800 mm in diameter and occur in the peat matrix. Pollen-filled fecal pellets are 50-150 mm in size and occur closely associated with cones, usually between cone scales. Whereas pollen in pollen-filled coprolites is often recognizable, pollen in fecal pellets is tightly packed, crushed and broken. In a random sample of 114 cordaitean cones recovered from the Williamson No. 3 Mine deposit (Kalo Formation, mid-Moscovian, Pennsylvanian) in Iowa, approximately 25% of the cones contained undispersed pollen grains and pollen-filled fecal pellets.

In modern peat from Florida, Taxodium (cypress) pollen occurs dispersed in the peat matrix. Although Taxodium pollen cones occur commonly in the surface peat, these cones do not have dispersed pollen clinging to cone scales, and do not contain fecal pellets. Wet sieving of Taxodium peat revealed abundant fecal material derived from terrestrial arthropods that were filled with vegetative debris; however, no fecal pellets contained pollen grains.

Despite the lack of pollen-filled fecal pellets and fecal material in modern Taxodium peat, many terrestrial arthropods eat pollen, either as predators, consuming undispersed pollen from cones and flowers, or as detritivores consuming pollen from the soil surface: collembola, mites, orthopterans, thysanopterans (thrips); lepidopterans (moths and butterflies); hymenopterans (bees), coleopterans (beetles) and dipterans (flies). Of these groups, lepidopterans, hymenopterans, coleopterans and dipterans radiated after the Pennsylvanian. The scarcity of concentrated accumulations of pollen (i.e., pollen-filled fecal pellets and cones with undispersed pollen) in modern peat may be due to the rapid recycling of a protein-rich substrate (pollen) rather than the absence of arthropod consumers in the mire. The common occurrence of concentrated accumulations of pollen from Pennsylvanian peats suggests that pollen recycling was slower in Paleozoic mires.