Meeting Abstract
A dramatic range of morphologic variation can be found within the basic avian body plan, a product of birds’ radiation into nearly 10,000 extant species that occupy a diverse set of niches. The great ecological diversity of birds is particularly apparent in terms of the remarkable variety of locomotor strategies they employ, from nimbly hovering hummingbirds and soaring albatrosses to deep-diving auks and cursorial ostriches. To assess how diversification of locomotor modes has impacted the evolution of avian pelvic morphology, we conducted a 2D geometric morphometric analysis of bird pelves from 165 species (n = 263) across all Aves. Pelvic morphology was captured by placing landmarks and semilandmark curves on photographs of the ilium and ischium of each specimen, in separate dorsal and lateral analyses. The bird species were categorized by locomotor group to determine how morphologic variation is related to hindlimb function. We found that the locomotor categories were significantly discriminated in morphospace (F = 15.903, p = 0.001). Phylogeny was also significantly correlated with shape (K = 0.409, p = 0.001), but in phylogenetically-corrected analyses functional grouping remained significant (F = 4.61, p = 0.008). Birds adapted for hindlimb-propelled swimming were particularly differentiated, with narrow, highly elongated ilia. Hyperaerial birds such as hummingbirds and swifts grouped at the opposite end of morphospace, with relatively squat pelves. Other locomotor groups plotted at various points between these two extremes of form and function, suggesting that iliac elongation in Aves reflects an increase in functional attachment area for hip musculature.
