INTERNAL NASAL ANATOMY IN BATS

         I have an ongoing interest in internal nasal anatomy that stems from my dissertation work and my work as a  Gerstner Scholar Postdoctoral Research Fellow at the American Museum of Natural History (AMNH) in New York, NY. While at AMNH, I studied how presence of paranasal sinuses affects evolution of skull shape in bats. My dissertation research on carnivore frontal sinuses suggested that they develop where bone is not structurally necessary, and, thus, economize skull structure and function. Sinuses may also facilitate evolution of novel skull shapes due to the fact that when they form, the bones they fill are separated into two separate plates; the inner plate that conforms to internal structures, such as the nasal chamber or braincase, and the external plate that allows external shape to be modified to meet the mechanical demands of diet or coopted for a variety of other functions. Presumably, without sinuses, changes in the shapes of the bones of the face would have a greater effect on the structure and function of the nasal chamber, braincase, etc., and/or may require development and maintenance of a greater amount of costly bone tissue.

 

 

 

 

 

 

 

 

 

 

 

 

Bat skulls are often extremely small (photo on left), but by using high-resolution micro-CT scans, I can easily study thier anatomy, including the insides of skulls all without damaging the original specimen. The four skulls on the right are digital replicas of real bat skulls like that in the photo to the left, and reveal differences in the size, number, and shape of paranasal sinuses adjacent to the nasal fossa.

 

        Bats represent over 20% of all living mammal species, and show remarkable skull shape diversity that rivals that of nearly all other mammal species combined. In addition, their compact size makes it possible quickly and easily compile a large number of high-resolution micro-CT scans of bat skulls in order to examine paranasal sinus morphology throughout the clade. Like carnivores, skull shape in bats is related to how they use their skulls. Much of the variation in bat skull shape is related to diet, but bats show additional features that are related to flight and echolocation. Thus, bats offer an excellent framework within which to test how paranasal sinuses affect evolution of skull shape disparity, and also how this is related to species diversity.

 

 

 

 

 

 

 

 

 

 

 

 

Illustrations based on micro-CT data showing differences in the shape of the nasal chamber and morphology of the delicate turbinal bones in three species of emballonurid bats (Left to right: Taphozous, Emballonura, Balantiopteryx). Note the honeycomb-like texture of the turbinals in Emballonura and Balantiopteryx, which are associated with presence of expansive paranasal sinuses.

 

          The internal anatomy of bat skulls is poorly understood, however use of non-destructive high-resolution micro-CT scans allows me to study anatomy previously obscured and inaccessible without use of destructive methods. CT scans are revealing that paranasal sinuses are much more widespread in bats than thought by previous authors, and are even found in the smallest species of bats.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Three-dimensional reconstructions of horseshoe bat skulls illustrating the unique form of the maxilloturbinal (orange) and differences in the lengths of the lateral and medial strands of the maxilloturbinal among species. A: Rhinolophus affinis, B: Rhinolophus mehelyi, C: Rhinolophus hipposideros.

 

     In addition to paranasal sinuses, CT scans allow me to study variation in the size and shape of the nasal chamber and associated turbinal bones, as well as other features of the nasal chamber and cranium, and have led to the discovery of several novel features in some groups of bats. Most notable, are the unique strand-like turbinal bones in the nasal chambers of horseshoe bats (Family Rhinolophidae); a group of bats highly specialized for nasal emission of echolocation calls.