Ecological Correlates of the Morphology of the Auditory Bulla in Rodents: Applications to the Fossil Record
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Date
2020-12
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The Ohio State University
Abstract
For rodents, hearing is essential to survival; it enables predator evasion, prey detection, and conspecific recognition. The hearing system of rodents is likely to be ecology-specific since hearing is constrained by the surrounding physical environment. Previous research on the middle ear of rodents shows this ecomorphological association. The link between tympanic bulla morphology and ecology has never been investigated across a broad array of rodent species before; such link may enable the determination of the ecological affinities of many fossil species only known from partial skulls. In this study, I use geometric morphometrics to quantify the shape of the auditory bulla of 197 specimens of extant rodents representing 91 species from 17 families across four different locomotory modes. I use landmarks and semi-landmarks on the ventral and lateral views of the skull to capture characteristics of bullar inflation and external auditory meatus extension. The results of my principal component analyses and canonical variate analyses demonstrate an association between bullar morphology and locomotion in rodents. The classification phase of my combined analysis of the two views enables the correct classification of 76% of the species in the training set. A phylogenetically-informed flexible discriminant analysis shows a weak phylogenetic effect on tympanic morphology. The application of this approach to select fossil rodents from the Oligo-Miocene shows broad agreements with prior studies and yields new locomotory inferences for 17 fossil species, including the first proposed locomotion for members of the family Florentiamyidae. Such results call for the timing of burrowing diversification in rodents to be reevaluated.
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Keywords
morphology, Rodentia, geometric morphometrics, paleoecology