POLLEN-FILLED COPROLITES IN MIDDLE PENNSYLVANIAN CORDAITEAN CONES: EVIDENCE FOR EARLY POLLINOVORY IN CORDAITEANS?

Pennsylvanian coal balls contain rich assemblages of plant debris and invertebrate traces, serving as our primary resource for understanding paleoecological interactions in Pennsylvanian peat swamps. Cordaitean cones in coal balls often contain arthropod coprolites. Previous studies reported the occurrence of coprolites filled with cordaitean pollen in cordaitean cones and used coprolite size to identify the organisms that may have produced them. Here we analyze their frequency and report their spatial distribution in cones and the peat matrix. Our dataset consists of 192 cordaitean secondary cones on 83 mounted slides from the Cliffland coal bed of Iowa, from the Harvard University Paleobotanical Herbarium, analyzed using light microscopy. We identified two types of coprolites, coprolites filled with partially digested vegetative organs (dark in color; 30%) and pollen-filled coprolites (golden in color; 70%). Pollen-filled coprolites primarily occur within mature cordaitean cones (98% occur inside the cone scales of mature pollen cones) and are composed of cordaitean pollen (Florinites). Immature cones did not contain pollen-filled coprolites. Dark coprolites are common in the peat matrix, however, a few occurred with pollen-filled coprolites in cordaitean cones. Coprolites in cones range in size from 70 μm to 150 μm and were spherical in shape and resemble those of mites and collembola. The minimum percentage of pollen cones with pollen-filled coprolites was 44%. Coprolites in peat may be derived from a number of sources, including arthropods that ate living material within the forest canopy or on the forest floor (herbivory), and arthropods that consumed dead plant, fungal or animal debris in the peat (detritivory). The high percentage of pollen-filled coprolites confined to mature cordaitean pollen cones (98%) suggests that these coprolites resulted from pollen predation in the canopy before cones fell to the forest floor. Dark coprolites in pollen cones may derive from sterile or fertile cone scales and pollen sacs consumed to access pollen. Pollen-filled coprolites in cordaitean pollen cones may be the earliest occurrence of pollinovory in gymnosperms.