Using pre-Quaternary Diptera as indicators of paleoclimate

Abstract

Many researchers have used fossilized insects to determine Quaternary climates with great success. However, pre-Quaternary insect fossils have not been utilized as indicators of climate with the same frequency, despite levels of preservation that are often equal to that of Quaternary fossils. In this study we use the Mutual Climate Range (MCR) approach with fossil Diptera from the Florissant Formation to examine the accuracy with which pre-Quaternary insect fossils can be used to determine paleoclimate. A database of extant Dipteran climate ranges was compiled and MCR analyses were performed on all fossil Dipteran genera from Florissant with extant representatives. The analyses were performed using all fossil Dipteran genera and then again with only non-host-specific taxa. The estimates of paleoclimate from our analyses were then compared to previous estimates obtained from various paleobotanical studies of the Florissant Formation. The paleobotanical studies utilize a variety of methods to determine paleoclimate, including nearest living relative (NLR), modern analogues, CLAMP, palynalysis, and leaf margin analysis. We found that using a MCR approach with fossil Diptera can provide an estimate of paleoclimate for pre-Quaternary assemblages that is consistent with estimates made by paleobotanists. The analysis that included all Diptera gave a less precise climate estimate (12–18 °C) than the analysis in which host-dependent taxa were omitted. Our climate estimate, based on only non-host-specific taxa, was 12–14 °C, which is well within the range of estimates for Florissant derived from floral material. Although approaches that use modern analogs are sometimes viewed with concern because of the necessary assumption that fossil taxa share the same environmental tolerances as their modern counterparts, we believe that fossil insect assemblages, especially when used in MCR analyses, can be quite informative in estimating pre-Quaternary paleoclimate.