Science Daily mentions an interesting paper on the relationship between brain size, body, and longevity in mammals. From Science
The study includes an extended taxonomic range in comparison to previous studies and takes into account phylogenetic relations between species analysed. Researchers analysed a series of other variables which could be related to higher longevity, such as metabolic rates — the amount of energy expended while at rest — diet or habitat, and concluded that none of these can be significantly associated with longevity. Connections are made however not only with a larger brain size, but also with a larger body size, given that large animals are known to live longer. Nevertheless, CREAF researchers confirm that the size of the brain affects lifespan regardless of the size of the body. Hyenas, for example, have a larger brain than giraffes in proportion to body size and on average live longer, although they are smaller than these herbivores.
The study looked at 493 mammal species and can be found here (this links to the pdf – which is open access).