Relative volume of the cerebellum in dolphins and comparison with anthropoid primates

According to the 'developmental constraint hypothesis' of comparative mamma lian neuroanatomy, brain growth follows predictable allometric trends. Ther efore, brain structures should scale to the entire brain in the same way ac ross mammals. Evidence for a departure from this pattern for cerebellum vol ume has recently been reported among the anthropoid primates. One of the ma mmalian groups that has been neglected in tests of the 'developmental const raint hypothesis' is the cetaceans (dolphins, whales, and porpoises). Becau se many cetaceans possess relative brain sizes in the range of primates com parative tests of the 'developmental constraint hypothesis' across these tw o groups could help to delineate the parameters of this hypothesis. In this paper, we compare relative cerebellum volumes in two cetacean species, the bottlenose dolphin (Tursiops truncatus) and the common dolphin (Delphinus delphis) with published data from anthropoid primates. We found that relati ve cerebellum size is significantly greater in the two dolphin species than in any of the primates, including humans. These results suggest that there is possibly expansion of brain structures independent of strictly allometr ic processes. Copyright (C) 2000 S. Karger AG, Basel.