Also, because people may miss the edit, I wonder about their diet as well. Where does the protein for the muscle mass come from? Their size tells us a lot; homosapien generations seem to have increased in height from their primitive predecessors. I remember reading that an increased height and erect spine actually causes greater body heat emission, whereas our hunched ancestors could avoid detection due to their physiology. For oxygen, we would HAVE to assume that some plant or aerobic bacteria thrives deep underground. This would suggest H2O, say for the cyanobacteria, which are responsible for the chemical synthesis of Oxygen.