WERE PENNSYLVANIAN MICROARTHROPODS PREDATORS OF CORDAITEAN POLLEN?

Pollen-filled fecal pellets and coprolites could result from either pollen predation or detritivory. Distinguishing between the two depends on determining the location of pollen consumption. When soil arthropods consume undispersed pollen in cones and sporangia within the peat, this is detritivory. When arthropods consume undispersed pollen in cones and sporangia attached to the living plant, this is pollen predation. Pollen-filled fecal pellets found in close association with cordaitean pollen cones from the Kalo Formation (mid-Moscovian) of Iowa suggest that Pennsylvanian microarthropods may have been predators of cordaitean pollen. Coal balls from the Kalo Formation contain a diverse assemblage of cordaiteans seeds (Cardiocarpus, Mitrospermum, and Nucellangium). Medullosan seed plants contributed up to 45% of the debris in these swamps. However medullosan pollen was large and rare compared to cordaitean pollen; and all pollen-filled fecal pellets associated with medullosan debris appear to represent coprophagy. Psaronius tree ferns contributed up to 15% of the plant debris in coal balls from the Kalo Formation; however Psaronius spores rarely occur in fecal pellets or coprolites.

Pollen-filled fecal pellets associated with cordaitean cones range from 20 – 50 microns in diameter, and could have been produced by oribatid mites, collembola, or another, unknown group of microarthropods. The following evidence suggests that these fecal pellets resulted from pollen predation: 1, In cordaitean peat, pollen-filled fecal pellets always occur between cone scales and have not been found within the peat matrix of coal balls. Fecal pellets in this location could have formed when the cones were attached to the tree, and fallen into the peat with the cone. Fecal pellets within the peat matrix are peat-filled. 2, The pollen in fecal pellets associated with cordaitean pollen cones is macerated, suggesting that the consumers derived nutrition from pollen.

Spore-filled fecal pellets from the Early Devonian Rhynie Chert were hypothesized to result from detritivory. Unmacerated spores in these fecal pellets were interpreted as an undigested, indigestible residue, excreted by soil microarthropods. If so, we would expect these fecal pellets to contain undigested plant material mixed with spores.