Subarcuate Fossa Anatomy as an Indicator of Future Locomotor Behavior in Newborn Primates.

Previous studies have demonstrated a link between subarcuate fossa size and locomotor behavior in primates. This fossa contains the petrosal portion of the paraflocculus, a portion of the brain associated with mobility and motor control. Studies have determined that the size of the fossa is larger in primate species that have more complex forms of locomotion. This study tested whether size of the subarcuate fossa in newborns predicts adult locomotor behavior. The sample included adult and newborn individuals of species representing strepsirrhine, tarsier, and platyrrhine primates. MicroCT images were used to create virtual endocasts in 3DSlicer software. The subarcuate fossa was isolated, and the volume was measured for each specimen. Results demonstrated that newborns from species with higher levels of locomotor agility exhibit a larger subarcuate fossa at the time of birth than newborns from species with lower levels of locomotor agility. This confirms that the subarcuate fossa is an indicator of the future locomotion of the primate. Comparison of subarcuate fossa volume between newborn and adult scans from the same species indicated that there is little growth in the fossa from birth to adulthood in most primates. These results are consistent with an expectation that the size of the subarcuate fossa is highly constrained by the semicircular canals, which are not expected to increase in size through growth. The possibility exists that the size of the semicircular canals is the object of selection, and the size of the subarcuate fossa is a secondary effect. These findings show that this aspect of a newborn primate's anatomy expresses information about its future behavior prior to any experience with locomotor action.