Meeting Abstract

P1.94  Wednesday, Jan. 4  Frontal Sinus Morphology in Arctoid Carnivorans CURTIS, Abigail A.*; LAI, George; VAN VALKENBURGH, Blaire; Univ. of California, Los Angeles

Frontal sinuses are one of four mammalian paranasal sinuses that form when nasal epithelium escapes the nasal chamber and invades surrounding bones including the maxilla, sphenoid, ethmoid, and frontal. Sinuses appear to form where bone is mechanically unnecessary. Aquatic mammals are generally cited as lacking frontal sinuses, and it is presumed that they are lost due to negative effects of having air filled spaces during diving. To date, there has not been a quantitative study how sinus morphology varies with degree of aquatic lifestyle. Here we quantified frontal sinus anatomy in arctoid carnivorans including bears, seals, skunks, otters, raccoons, and weasels. Arctoids offer a number of independent acquisitions of aquatic behavior that range from fully terrestrial to almost exclusively aquatic, as well as a broad range of body sizes. We expect aquatic species will have no sinuses, and semi-aquatic species will exhibit relatively reduced sinuses relative to terrestrial species, reflecting their intermediate behavior. We used CT technology to construct volumetric models of frontal sinuses and quantified size and 3-dimensional shape using spherical harmonics. As expected, sinuses are absent in aquatic species and reduced in semi-aquatic species. Notably, the American badger and kinkajou (both terrestrial) lack sinuses. Aquatic species tend to have flatter skulls with enlarged, dorsally shifted orbits. The fossorial badger exhibits a similar trend in skull shape, whereas the frugivorous kinkajou has an extremely foreshortened snout. Thus we propose that the absence of sinuses in aquatic arctoids is not likely an adaptation for diving; rather it reflects skull shape changes that improve vision and streamlining for crypsis and/or swimming efficiency.