Monkeying around with bat scapulae: Old World fruit bats show arboreal adaptations of primates lacking in New World fruit bats

Abstract

Comparative analysis of nonflight morphologies can give important insight into the early ancestral origin of bats by revealing locomotor adaptations that may have predated wings. Because the scapula of bats is not directly involved in flight mechanics but does retain a primary role in walking and climbing, morphological analysis may help resolve if the ancestor to bats was arboreal or terrestrial as well as if bats are indeed monophyletic. We compared the scapulae of species representing the body mass range of Old World fruit bats (Pteropodidae) with those spanning the body mass range and diverse diets of New World fruit bats (Phyllostomidae), with a focus on the subfamily Stenodermatinae whose members have very similar niches to pteropodids. Because we were interested in scapular traits associated with climbing versus walking, we analyzed characters known to differentiate arboreal from terrestrial primates, in both contemporary and extinct lineages. We hypothesized that the scapulae of both fruit bat families would show similar adaptations, either for terrestrial or arboreal locomotion, especially if they were derived monophyletically. We found that pteropodids scapulae showed overall adaptations associated with climbing and suspensory locomotion similar to arboreal primates, whereas phyllostomids possessed character states indicating terrestrially adapted scapular morphology. Comparing the scapulae of contemporary species with the scapulae from full-bodied fossil bats from the Eocene and Oligocene epochs showed alignments that may depict the evolutionary underpinnings of each group's adaptations.