Estimates of climate derived from the foliar physiognomy of modern vegetation indicate that, for modern test sites, the calculated climates can differ from actual climates and are sensitive to the equation used to quantify the leaf/climate relationship (or transfer function). To determine how estimates of past climates can vary in response to transfer function, we analyzed a latest Cretaceous (Maastrichtian) leaf assemblage from the Jose Creek Member of the McRae Formation, southern New Mexico, in part because of its relevance to climatic change across the Cretaceous-Tertiary boundary. The Jose Creek assemblage represents probable in situ leaf litter preserved in volcanic ash and was derived from vegetation growing in well-drained soil. The analyzed assemblage consists of 132 specimens of dicot leaves belonging to 43 species, which are associated with a comparable number of ferns, conifers, and thermophilic monocots belonging to at least 10 species. Estimates of mean annual temperature (MAT) and mean annual precipitation (MAP) were made using published univariate and multivariate transfer functions derived from the CLAMP database of Wolfe or regional floras. Calculations were made using raw physiognomic data and data adjusted to account for the over-representation of small leaves in modern leaf litter. Calculated MAT for the Jose Creek assemblage generally ranges from 16-21C, with multivariate transfer functions tending to give cooler values than univariate transfer functions. Calculated MAP ranges from under 800 to over 1500 mm per year, with an average of 1100 mm. Variation in calculated temperature and precipitation, relative to the mean of all estimates, can exceed 35%, underscoring the potential bias introduced by choice of transfer function. However, the range of values is congruent with more qualitative estimates of climate derived from fossil soils and plant life form, which indicate warm moist conditions and above-freezing cold-month means for the Jose Creek Member.

Key words: Cretaceous, paleobotany, paleoclimate, physiognomy