ESTIMATING CLIMATE FROM THE LATE CRETACEOUS FLORA OF THE TWO MEDICINE FORMATION, MONTANA: COMPARISON OF UNIVARIATE METHODS AND DIGITAL LEAF PHYSIOGNOMY
This study uses LMA, LAA, and DiLP to reassess the paleoclimate inferred from the fossil flora of the Upper Cretaceous Two Medicine Formation of Montana. The specimens used in this study are twenty-nine morphotypes of fossil dicotyledon (dicot) leaves collected from the lower part of the formation near Cut Bank, Montana by David Crabtree. Crabtree estimated MAT of 7–10 °C with no extended cold season, based on LMA and the presence of fossil palms.
In this analysis, DiLP estimates a MAT of 17°C, whereas LMA estimates a lower temperature of 10°C. DiLP and LAA estimate MAP of 108 and 91 cm, respectively, values characteristic of a subhumid climate. The temperature offset between DiLP and LMA for the Two Medicine flora is comparable to temperature offsets found for Maastrichtian and Paleocene floras from the northern Western Interior. The DiLP estimate of MAT is more in line with published temperature estimates for the Campanian of North America, which may indicate that it provides the more accurate estimate of temperature for the Two Medicine flora.