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The uppermost Eocene Florissant Formation of central Colorado, U.S.A. contains a diverse flora and fauna preserved in lacustrine facies and represents a key episode in Earth history immediately preceding the Eocene-Oligocene boundary. Laminated shales contain impressions of non-monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods including: leaf mass per area (M A), digital leaf physiognomy (DiLP), leaf margin analysis (LMA), and leaf area analysis (LAA). The majority (58%) of the morphotypes analyzed for M A suggested a semi-evergreen leaf lifespan, whereas another 27% indicated a deciduous habit and 15% an evergreen habit. There was no significant relationship between M A and insect damage based on a small subset of Florissant's leaves. Higher M A values (~73% of leaves ≥ one-year lifespan), coupled with a tendency toward long and narrow leaf shapes and small leaf areas, indicate the existence of sclerophyllous vegetation. Using the global regression for mean annual temperature (MAT), the DiLP estimate of MAT was anomalously cold: 5.5 ± 4 °C. However, using a Northern Hemisphere regression the DiLP MAT estimate of 11.6 ± 3.3 °C was more plausible. Using DiLP, mean annual precipitation (MAP) was estimated at 740 + 608/−334 mm∙yr−1, which supports dry conditions. Estimates for MAT and MAP using the univariate LMA and LAA methods overlapped within uncertainty of the DiLP results. In addition, those taxa classified as growing in wet areas (riparian) had significantly more teeth than non-riparian taxa. These paleoclimatic and paleoecological results suggest that outside the riparian forest, the Florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland, perhaps similar to modern chaparral forests, in the western interior of the U.S.A. just before the transition into the cooler Oligocene. • The uppermost Eocene Florissant Formation in Colorado preserves a diverse flora. • The majority of morphotypes indicated a leaf lifespan of approximately one year. • Mean annual temperature for Florissant was estimated to be 11.6 ± 3.3 °C. • Mean annual precipitation was estimated at 740 + 608/−334 mm∙yr−1. • Florissant provides key climate data just before the transition to the Oligocene. [ABSTRACT FROM AUTHOR]

We tested the sensitivity of paleoclimate estimates to different resolutions of leaf morphotype distinction by grouping one paleofloral collection three ways and comparing the results. We examined the different morphotype resolutions using a recently collected Eocene (34 Ma) fossil leaf assemblage from Florissant Fossil Beds National Monument Collection Site 9 (CS-9, Florissant, Colorado), an exposure that yields one of the most diverse sets of dicotyledonous angiosperm ('dicot') morphotypes yet analyzed from a single site within this well-studied formation. We grouped this collection using what are herein referred to as 'Splitter' (number of morphotypes n = 129), 'Intermediate' (n = 96), and 'Lumper' (n = 53) morphotyping approaches, which differed in their degree of delineating foliar morphotypes. Leaf Margin Analysis (LMA) and Leaf Area Analysis (LAA) were used to obtain paleotemperature and paleoprecipitation estimates from the morphotype datasets and Climate Leaf Analysis Multivariate Program (CLAMP) was employed to examine further parameters. We perform an additional paleoclimatic analysis of CS-9 in which we divide the site into three stratigraphic sections, and finally we perform an analysis on sample collections above and below a volcanic event horizon within CS-9. Whole collection results across the three morphotype resolutions indicate a mean annual temperature between 10.8 and 12.5 °C, and annual precipitation between 61.8 and 130.7 cm at the time of deposition. The 'Splitter,' 'Intermediate,' and 'Lumper' approaches provide very similar estimates by all methods of analysis and suggest that morphotype resolution specificity has very little effect on climatic results using these leaf physiognomic techniques. • Different fossil leaf morphotype resolutions yield similar paleoclimate estimates. • By our methods, lower morphotype resolution generates colder and wetter estimates. • Leaf physiognomy estimated a mean annual temperature of ~12 °C for Florissant. • Mean annual precipitation was estimated between 620 and 1310 mm using leaf physiognomy. • This furthers our understanding of regional climate before a global cooling event. [ABSTRACT FROM AUTHOR]