Unique frontal sinuses in fossil and living Hyaenidae (Mammalia, Carnivora): description and interpretation

ABSTRACT

Unique, caudally elongated frontal sinuses 2′ (terminology of Paulli, 1900c) are present in the living hyaenine hyaenids (Crocuta crocuta, Parahyaena brunnea, Hyaena hyaena) and in at least four fossil hyaenids (Adcrocuta eximia, Hyaenotherium wongii, Palinhyaena reperta, and Ictitherium viverrinum). In Crocuta crocuta, Parahyaena brunnea, Hyaena hyaena, 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 enough to indicate a persistent difference in skull architecture between proteline and hyaenine hyaenids through time. The elongated frontal sinuses in all hyaenids examined in this study except for Proteles is an impressive pattern, and its potential function is unlikely to be related to shock dissipation, brain cooling, olfaction, or maximization of muscle attachment area. With the application of basic structural engineering 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 mammalian sagittal crest.