Leaves as Thermometers
In 1979, Jack Wolfe of the USGS published a landmark observation: in forests worldwide, the proportion of tree species with smooth-edged (entire-margined) leaves increases linearly with mean annual temperature. Tropical forests have 60-80% entire-margined species; temperate forests have 20-40%. This simple relationship — leaf margin analysis — became one of paleobotany's most powerful tools for estimating ancient temperatures from fossil leaf assemblages.
The Calibration
The original Wolfe regression (MAT = 1.14 + 30.6 * P, where P is the fraction of entire-margined species) was calibrated on East Asian forests. Subsequent global calibrations by Wilf, Wing, Greenwood, and Peppe have refined the slope and intercept, finding slightly different values for different continents and time periods. This simulator uses the classic Wolfe calibration by default but lets you adjust the regression parameters to explore alternative calibrations.
Counting Species, Not Specimens
A critical methodological point: LMA counts species, not individual leaves. A flora dominated by one toothed species should not bias the temperature estimate. Each species is scored as either entire-margined or non-entire, and the percentage is computed. This species-level approach requires careful taxonomic identification, which is challenging with fragmentary fossils. Most studies require a minimum of 25-30 morphospecies for statistical reliability.
Beyond Simple Margins
Modern multivariate approaches like CLAMP (Climate-Leaf Analysis Multivariate Program) and Digital Leaf Physiognomy extend LMA by scoring dozens of leaf traits — tooth size, tooth density, apex shape, leaf area, length-to-width ratio — and using multivariate regression against multiple climate variables. These methods can estimate not just MAT but also precipitation, growing season length, and humidity. The simple univariate LMA remains popular for its transparency and ease of application.