Two major evolutionary events shaped current vertebrate life forms: the transition from water to land during the Carboniferous period and the development of endothermy during the Triassic period (Freeman and Herron, 1998). Nascent terrestrial animals experienced new ecological opportunities because of the water to land transition, while at the same time they confronted new physiological challenges such as maintaining an aqueous internal milieu in a desiccating environment (Gordon and Olson, 1995). With the advent of endothermy, land animals may have increased their fitness, but their need for energy must have risen by as much as an order of magnitude compared to their ectothermic ancestors (Bartholomew 1982; Bennett and Dawson, 1976). Endothermy also exacerbated problems of water loss because high rates of metabolism were associated with elevated respiratory water loss as well as increased water loss via urine and feces.