Paleoclimate of the Two Medicine Formation based on Leaf Physiognomy
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Over the past 50 years, methods to study ancient warm climates, like those of the Cretaceous, have yielded new information on climates and their interaction with flora and fauna. One of the effective ways to reconstruct paleoclimates in terrestrial environments is the study of external features of leaves, or foliar physiognomy. Features of leaves from different climates have been correlated to mean annual temperature (MAT), mean annual precipitation (MAP), and other climate variables. There are several methods to determine paleoclimate based on the modern-day correlation between leaf features and climate parameters. These methods include the univariate methods of leaf margin analysis (LMA) and leaf area analysis (LAA), and the multivariate methods of Climate Leaf Analysis Multivariate Program (CLAMP) and Digital Leaf Physiognomy (DiLP). This study uses these paleoclimate proxies to study the Two Medicine Formation, a famous formation in northern Montana that contains both dinosaur and paleobotanical remains. In addition, the research examines the congruence of different physiognomic methods with each other and with other climate proxies for the Two Medicine Formation and surrounding formations of similar age. This study concludes that the univariate methods give temperature estimates that are too low, and the multivariate methods give precipitation estimates that are too high. Of the two multivariate methods, CLAMP gives slightly lower temperature estimates and has inconsistencies based on classification of leaf features, but is still able to provide seasonality signals. DiLP, on the other hand, gives more reasonable estimates for MAT based on congruence with other paleoclimate proxies. However, the DiLP image processing of the leaves is more complex and time consuming than that of the other methods. In order to cute the leaf image processing time, a new modified technique of doubling the leaf halves from partial fossil specimens was implemented in this study. Preliminary results from the doubling halves technique indicates that climate parameter estimates are nearly the same as those described in the original DiLP method.