Our analysis has illustrated that within Procyonidae there are two distinct modes of metabolic adaptation to climate. One is typified by those species with low [.H]_{ b}'s (_Bassariscus astutus_, _Nasua nasua_, _Nasua narica_, _Procyon cancrivorus_, and _Potos flavus_), and the other by _Procyon lotor_ with its higher [.H]_{ b}. Those with low [.H]_{ b}'s have more restricted geographic distributions, and, with the exception of _Bassariscus astutus_, they are all confined to tropical and subtropical areas. The fossil history of this family indicates that it had its origins in tropical forests of North and Central America. This indicates that those procyonids whose distributions are still primarily restricted to tropical forests share many of the metabolic adaptations characteristic of their ancestors. We speculate, therefore, that ancestral procyonids had a lower than predicted [.H]_{ b}, a pelt with modest to poor insulative quality, good thermogenic ability but poor heat tolerance, modest to poor capacity for evaporative cooling, no well-defined molt cycle, no cyclic period of fattening, nocturnal habits, and a modestly diverse diet of high-enough quality to provide for an average reproductive potential. Although this pedigree contributed to the success of this family in tropical and subtropical forests, it limited the ability of its members to expand their distributions into cooler, less stable climates. Viewed in this perspective, _Procyon lotor_'s high basal metabolic rate, extraordinarily diverse diet, well-defined cyclic changes in fat content and thermal conductance, high level of heat tolerance, high capacity for evaporative cooling, and high reproductive potential all stand out in sharp contrast to the condition described for other procyonids. This suggests that the North American raccoon represents culmination of a divergent evolutionary event that has given this species the ability to break out of the old procyonid mold and carry the family into new habitats and climates.
a potential age of females first producing young
b potential annual birth rate of female young
C_{ mwr} ratio of measured to predicted minimum wet thermal conductance
D_{ dr} ratio of food categories actually used by a species to the total number of food categories taken by all species tested