Angiosperm leaf megafossils from the southern Rocky Mountains will be surveyed to determine patterns of generic and familial diversity in floral assemblages bracketing the Cretaceous-Tertiary boundary (66 million years b.p.), one of the five major extinction episodes in the history of life. Although species-level analyses of pollen and leaf assemblages have elucidated many details of climatic and ecological change at this time, many biological properties of plant extinction cannot be determined accurately, because leaf megafossils must be determined through detailed analysis of foliar venation and cuticular anatomy in well-preserved remains and extensive comparisons with reference collections of extant angiosperm leaves. This analysis will provide more reliable determinations of systematic relationships than are currently available for latest Cretaceous and earliest Tertiary paleofloras, in assemblages that have tight stratigraphic age control. These systematic determinations will provide a data base for future quantitative analysis of end-Cretaceous plant extinction, which will be important for testing hypotheses on the nature of biotic extinction.
