Table 1.

Examples of ecometric traits that can be applied to modern and fossil organisms.

Leaf physiognomy. The average shape of leaf serrations and lobes in dicot communities are related to mean annual temperature and water stress [59,97] (figure 2a). These traits are used to estimate continental climate conditions during the Mesozoic and Cenozoic from fossil floras [16,98–100].

Leaf venation density. The density of veins in the leaves of seed plants is related to transpiration and water availability, and it has been used to estimate these parameters from the Carboniferous to the present day [101].

Stomatal density. The density of stomatal pores on the surfaces of plant leaves and stems, through which carbon dioxide and oxygen are exchanged with the atmosphere, is inversely related to atmospheric CO2 concentration [38]. Stomatal density measured from fossil leaves tracks CO2 concentrations through the industrial era [102] and geological history [103].

Ectothermic body size. Metabolic rate decreases as body mass increases. Organisms cannot function with mass-specific metabolic rates below a certain threshold, placing a limit on the maximum size they can attain. In poikilotherms, whose internal temperature varies with the surrounding environment, mass-specific metabolic rate increases with ambient temperature, meaning that the maximum attainable size varies with environmental temperature [104,105]. The maximum size of terrestrial poikilotherms is a trait that has been used to estimate palaeotemperature [33] (figure 2c).

Limb proportions. The proportion of limb segments is related to stride length, speed and power in terrestrial vertebrates [106]. Arboreality, cursoriality and other locomotor styles differ in limb proportions. Because different macroenvironments favour different locomotor styles, average limb proportions in mammalian communities vary with macrovegetation and ecological region [71] (figure 2d).

Body mass. Body mass is related to ambient temperature, metabolic rate, substrate, diet and many life-history variables [107]. The analysis of body size in relation to mean annual temperature and macrovegetation is a well-developed ecometric example [34,108,109].

Tooth crown complexity. The shapes of the occluding surface of mammalian cheek teeth are specialized for food processing. The number of surface patches with the same occlusal orientation is smaller in carnivorous than in omnivorous and herbivorous teeth, making the ‘patchiness’ of the tooth crown highly correlated with the proportion of vegetation in the diet [17].