Abigail A. Curtis, Jessica H. Arbour, and Sharlene E. Santana
Novel morphological traits pose interesting evolutionary paradoxes when they become widespread in a lineage while being deleterious in others. Cleft palate is a rare congenital condition in mammals in which the incisor-bearing premaxilla bones of the upper jaw develop abnormally. However, ~50% of bat species have natural, non-pathological cleft palates. We used family Vespertilionidae as a model and linear and geometric morphometrics within a phylogenetic framework to (1) explore evolutionary patterns in cleft morphology, and (2) test if cleft morphological variation is correlated with skull shape in bats. We also used finite element analyses (FEA) to experimentally test how presence of a cleft palate impacts skull performance during biting in a species with extreme cleft morphology (hoary bat, Lasiurus cinereus). We constructed and compared performance of two FE models: one based on the hoary bat’s natural skull morphology, and another with a digitally filled cleft simulating a complete premaxilla. Results showed cleft length and width are correlated with skull shape in Vespertilionidae, with narrower, shallower clefts seen in more gracile skulls and broader, deeper clefts in more robust skulls. FEA showed that the model with a natural cleft produced lower bite forces, and had higher stress and strain than the model with a filled cleft. In the rostrum, safety factors were 1.59–2.20 times higher in the model with a filled cleft than in the natural model. Our results demonstrate that cleft palates in bats reduce biting performance, and evolution of skull robusticity may compensate for this reduction in performance.