(638.3) Comparative Growth of the Tympanic Cavity in Primates

Poster Board Number: C129
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Katheryn Franklin (University of Florida), Laura Haynes (University of Florida), Timothy Smith (Slippery Rock University), Valerie DeLeon (University of Florida)

Primate auditory structures are morphologically indicative of taxonomy and phylogeny.   The tympanic cavity houses the three articulating ear ossicles: malleus, incus, and stapes.  The ossicles amplify sound waves from mechanical vibrations to the cochlea, a sensory organ, where it can then be interpreted by the organism.  All primates are characterized by a petrous bulla, but the extent of the tympanic cavity varies across taxa.

            Our sample of newborn and adult individuals representing strepsirrhines (e.g., Galago moholi and Nycticebus pygmaeus) and haplorhines (e.g., Aotus nancymaae and Cebuella pygmaea) allowed us to study the comparative growth of these structures.  Using a combination of conventional CT data and diffusion iodine contrast-enhanced CT (diceCT) data, we created 3D models of auditory structures using 3DSlicer.  Metric data included angles between ear ossicles, surface area of the tympanic membrane, surface area of the stapes footplate, and overall tympanic cavity volume.  Many differences among major clades are already evident at the newborn stages in this sample.  The pneumatization of accessory cavities in newborns has been initiated. For example, in the newborn Galago moholi, pneumatization of accessory cavities is most pronounced posteriorly.  In contrast, in the newborn Aotus nancymaae, we see early evidence of the anterior accessory cavity.  Mesh-to-mesh comparisons of endocasts of the cavity indicate structural changes through ontogeny.  Additionally, the surface area of the tympanic membrane remains consistent through growth.

            This research allows for a better understanding of the relationship between the functional morphology of the auditory system and audible frequency levels. Haplorhines are adapted to lower frequencies than strepsirrhines. This adaptation is discernable at birth, and key spatial relationships of ossicles are maintained through ontogeny even as spatial configuration of the cranium as a whole undergoes profound change due to pneumatic expansion of sinus cavities and growth of soft tissue structures.  

Support or Funding Information

Funded by the National Science Foundation (BCS-1830894 and BCS-1830919)