Brains of Australian Chiroptera I. Encephalization and Macromorphology

Abstract

Data on brain weights and body weights of 87 individuals representing 20 species of Australian Chiroptera were analysed. The allometric equation: log brain weight = 1.655 + 0.684 log body weight, which was derived from data on the vespertilionid species except Tylonycteris spp.. was used to calculate indices of encephalization for Australian Chiroptera. Vespertilionidae and Molossidae have the lowest indices; those of Emballonuridae, Rhinolophidae and Hipposideridae are slightly higher, that of Macroderma gigas is distinctly higher, and the highest are found in the Pteropodidae. Accompanying this scale of increasing encephalization are increases in hemisphere length, cover of the mesencephalic tectum, and cerebral and cerebellar fissuration. All of the aerial insectivore and foliage-gleaning species belong to the less encephalized Chiroptera, whereas all fruit eaters (alone or combined with other trophic roles) are highly encephalized. The intermediately encephalized Macroderma is a combined carnivore and foliage-gleaning species.