It is somewhat dismaying, if not surprising, that so many trained biologists know that dinosaurs may have been “hot-blooded,” yet are completely unaware of even the existence of the mammal-like reptiles, the Therapsida. The reasons for the dearth of widespread knowledge of the therapsids are probably fairly mundane: the mammal-like reptiles are less spectacular in appearance than dinosaurs, and good therapsid fossil localities are restricted primarily to the southern hemisphere. As a result, therapsids seldom become the subjects of museum displays or classroom student presentations. Moreover, biology textbooks, whether at the high school or college level, almost invariably devote more space for recounting the “dinosaur story” than to discussing the therapsid reptiles (1). Consequently, although application of biological systems data to the fossil record has become increasingly popular and useful in the last decade, many neontologists who might potentially make substantial contributions to our knowledge of therapsid biology remain oblivious to the significance of these animals. This is particularly unfortunate—therapsids are, of course, the direct predecessors of mammals, and, as such, the more we understand the mammal-like reptiles the more likely we are to understand the origins and functions of our own anatomical, physiological, and behavioral systems.