Paranasal recesses and rostral airspace volume covary with echolocation call frequency in emballonurid bats

The mammalian rostrum has multiple functions including serving as the upper jaw, supporting olfactory sensory structures, conditioning inspired air, and-for some mammals-transmitting sound. Several groups of bats independently evolved bony inflations on the dorsolateral surfaces of their rostra. In rhinolophoid bats, rostral inflations are associated with nasal emission of echolocation calls, but their function in oral emitting bats (family Emballonuridae) is not well understood. Here, we combine μCT, diceCT, and histological methods to describe and quantify nasal fossa morphology of emballonurid bats in a comparative sample of 24 species overall, including 23 in the quantitative CT sample. Our goals are to (1) describe and quantify paranasal recess morphology, (2) explore scaling of paranasal recess size with body, skull, main nasal chamber, and turbinal size, (3) elucidate potential functions of rostral inflations in emballonurids, and (4) understand how nasal fossa morphology is related to presence of socially important glands and odor storing sacs in Emballonuridae. We report surprising diversity, clade-specific traits, and several novelties in paranasal recess size and location among emballonurids. The combined volume of the paranasal recesses and main nasal chamber was more strongly correlated with peak echolocation call frequency used during foraging than with skull size. Some emballonurid species possess a well-developed lateral nasal gland in the lateral recess. Other emballonurids have inflated, air-filled paranasal recesses lined with thin, avascular mucosa, similar to those of nasal emitters with rostral inflations. We also observed turbinal traits reminiscent of those in nasal emitting Rhinolophidae. Proportionally large paranasal recesses are associated with reduced size and turbinal elements in emballonurid bats, except possibly in species that exhibit complex mating displays using perfume storing sacs in their wing membranes. Together, our results suggest that paranasal recesses could play a role in modifying echolocation calls in Emballonuridae, as they are hypothesized to do in nasophonating bats. However, the potential acoustic function of paranasal recesses remains to be experimentally elucidated in bats.