Currently the majority of methods used to estimate paleo-elevation are based on the relationship of temperature with altitude, and for this reason, are inherently climate-sensitive. It remains difficult therefore to decipher the effects of changing elevation and broad scale global climatic change on these paleo-altimeters, which critically hampers our ability to evaluate or constrain theories relating to tectonic and climatic evolution. The reduction in CO2 partial pressure with altitude exerts a physiological limitation on plant photosynthesis, which is compensated for, in many species, by an increase in stomatal frequency (density and index) and altered stomatal distribution. This strong inverse relationship between stomatal frequency and atmospheric CO2 concentration, which has been repeatedly demonstrated experimentally and historically over the past 200 years of anthropogenic CO2 rise, has been successfully utilized to reconstruct paleo-CO2 concentrations on timescales of centuries to millennia. The accuracy with which paleo-CO2 concentrations can be estimated from sub-fossil and fossil stomata, and the observation that stomatal density and index increase with decreasing CO2 partial pressure with altitude, now offers the exciting potential of utilizing this relationship as a novel paleo-altimeter. A model for estimating paleo-elevation from fossil stomatal frequency will be presented and the implications of this new method discussed.

Key words: fossil plants, paleo-climate, paleo-elevation, stomatal density