OVERVIEW

The molar teeth of early mammals were less than a millimetre in length while those of a living African elephant are several hundred times larger. What is the reason for this? Well, it is probably true to say that, despite being a prime focus of investigation for a century or more, the adaptive significance of such tooth size differences is not understood. The initial approach here is to consider constraints not just on tooth size, but on the size of all mouthparts, that are imposed on the digestive system by the energy requirements of the mammalian body. The argument leads quickly to what engineers call ‘scaling arguments’. Biologists call them this too, but they also use the term ‘allometric analyses’. Both terms describe changes in the shape of animals required by change in their size. The predictions made here appear to be novel because they scale the mouth directly to the food particles that it ingests and not to whole body size (which is the norm in such studies). However, the arguments are couched in standard allometric form because this is the nature of the available data. Postcanines are treated separately from incisors and canines and both general arguments and specific roles are covered. The overriding philosophy is that physical properties of mammalian diets explain not only tooth size, but also the size of most orofacial structures.