A STUDY OF PLANT-INSECT INTERACTIONS IN THE PALEOCENE-EOCENE CHICKALOON FORMATION: PALEOECOLOGIC, PALEOCLIMATIC, AND PALEOLATITUDE IMPLICATIONS

The Paleocene/Eocene Thermal Maximum (PETM) was a relatively short period (~200ky) of global warmth that has been documented in the fossil and geochemical record by multiple marine and terrestrial paleoclimate studies. Recent studies of Paloecene and Eocene plant-insect interactions in middle-latitude North America (Wyoming and Colorado) have shown a positive correlation between the extent of insect damage on leaves and independent estimates of mean annual temperature (MAT). Both the frequency and types of leaf damage have been documented to guide these studies as they've examined this relationship before, during, and after this interesting phase in the Paleogene. Plant-insect interaction studies are scarce from higher latitude North America during this time however.

Here we examine a fossil leaf assemblage in the Late Paleocene/Early Eocene Chickaloon Formation in south-central Alaska; a fluvial depositional unit exposed now in the Matanuska Valley. This unit has preserved numerous foliage species, many of which show evidence of insect damage. In a collection of ~600 leaf specimens gathered from the Evan Jones Mine locality, ~8% showed at least one type of plant-insect interaction. Individual specimens in our collections exhibit margin feeding, hole feeding, and/or skeletonization. In comparison with Paleocene and Eocene collections from lower latitude localities, the insect damage frequency on Chickaloon Fm. leaves is low. These data provide valuable insight into complex paleoecological interactions among trophic levels in the Chickaloon ecosystem and may prove to be part of a dataset that can be used to test models of the paleolatitude of the unit's deposition. If the assemblage is shown to have been deposited in a high-latitude setting, the flora allows for examination of latitudinal effects on plant-insect interactions in the middle Paleogene, perhaps dealing with season severity and plant response to unique high-latitude seasonal light conditions.