THE PARANASAL SINUSES OF CAVIOMORPH RODENTS

Paranasal sinuses are air-filled cavities that surround the nasal cavity. The presence of these structures is a common trait of the mammalian skull, but in rodents these sinuses are rare. Here, we investigate the morphology of these cavities in extant and extinct caviomorphs, a clade of South American rodents. Fourteen specimens of neoepiblemids, chinchillids, dinomyids, erethizontids, caviids, hydrochoerines, dasyproctids, and echimyids were analyzed using computed tomography and three-dimensional reconstructions. In neoepiblemids, dinomyids, chinchillids, hydrochoerines, and erethizontids, a system of paranasal sinuses (frontal sinus, maxillary and lacrimal recesses, and their divisions) is present and located over the olfactory region of the nasal cavity. On the other hand, in some groups, such as caviids (non-hydrochoerines), dasyproctids, and echimyids, these structures are much reduced or absent. Comparing a newborn specimen of _H. hydrochaeris_ with an adult individual, it is possible to see that in early ontogenetic stages, the cavities are not fully developed, and the frontal sinus invades the frontal by bone remodeling through the ontogeny. The largest species of each clade show well developed frontal sinuses (covering the olfactory bulbs and the anterior region of the frontal lobes of the brain), while in smaller forms they are small or absent (i.e. not covering the anterior region of the brain). The development of paranasal sinuses is related to the increase in body size in clades of caviomorphs. Further, ongoing analyses of the distribution and shape of the paranasal sinuses and their volumes in a phylogenetic context are necessary for better understanding the evolution of these structures, their functionality, and origin in Caviomorpha. [CNPQ 422568/2018-0, CAPES 001, and SNSF grant 31003A-16939].