Growing apart: comparative cranial ontogeny in the myrmecophagous aardwolf (Proteles cristata) and the bone-cracking spotted hyaena (Crocuta crocuta)

Hyaenids represent an interesting case of extant low diversity but remarkable morphofunctional disparity. Hyaenas comprise three bone-cracking species, whereas the aardwolf ( Proteles cristata ) is a myrmecophagous species. Morphology of the skull and dentition reflects this functional disparity, and here we investigated postnatal ontogeny of the skull by applying multivariate allometry to 22 skull measurements taken in specimens from growth series of the spotted hyaena ( Crocuta crocuta ) and the aardwolf, which belong to hyaenid lineages that split in the middle Miocene or even earlier. We show that growth trends closely correspond to and explain the divergent morphofunctional patterning of the skull in each species. Interestingly, the smallest species —the aardwolf— showed a pronounced pattern of skull elongation, whereas in the spotted hyaena, the skull showed the strongest allometric trends in depth dimensions; these results reverse a general trend (CREA) of craniofacial elongation more pronounced in larger species, suggesting that specialization in dietary extremes can deviate developmental patterns from pervasive trends apparent in most mammalian lineages.