UNIQUE FRONTAL SINUSES IN FOSSIL AND LIVING HYAENIDAE (MAMMALIA, CARNIVORA) - DESCRIPTION AND INTERPRETATION

Unique, caudally elongated frontal sinuses 2' (terminology of Paulli, 1900c) are present in the living hyaenine hyaenids (Crocuta crocuta, P arahyaena brunnea, Hyaena hyaena) and in at least four fossil hyaenids (Adcrocuta eximia, Hyaenotherium wongii, Palinhynena reperta, and Ict itherium viverrinum). In Crocuta crocuta, Parahyaena brunnea, Hyaena h yaena, and Adcrocuta eximia, the elongated frontal sinuses completely overlie the brain cavity, a condition apparently unique in the history of the Carnivora. Elongated frontal sinuses are conspicuously absent in the extant aardwolf (Proteles cristatus), however. The cladogenetic distribution of these fossil and living hyaenid species is broad enou gh to indicate a persistent difference in skull architecture between p roteline and hyaenine hyaenids through time. The elongated frontal sin uses in all hyaenids examined in this study except for Proteles is an impressive pattern, and its potential function is unlikely to be relat ed to shock dissipation, brain cooling, olfaction, or maximization of muscle attachment area. With the application of basic structural engin eering principles, however, the elongated frontal sinus can be modeled as a shell structure that provides better resistance to muscular load than the cantilever plate geometry of the typical plate-like mammalia n sagittal crest.