Meeting Abstract
The vertebrate limb is a dynamic structure that often includes many endoskeletal elements yet has traditionally been analyzed via “static” measures of morphology such as length or mass. Can incorporating a structure’s dynamic capabilities help explain apparent gaps between form and function? For example, studies have repeatedly found that across broad investigations of avian clades, the correspondence between wing shape and flight behaviors is coarse. The avian wing, however, is well-suited to trace the evolution of motion capability: by modulating wing shape via skeletal joints, birds generate and control forces to keep themselves aloft. We measured the three-dimensional movement capabilities of wings from cadavers of 61 bird species from 20 avian orders, spanning a wide range of body masses and flight behaviors. These cadaver measurements were coupled with high-speed video of in vivo wing usage in three focal species. Using a phylogenetic comparative framework, we found that various aspects of range of motion strongly associate with flight behavior and/or body mass. In contrast, wing shape bears little correspondence to either explanatory variable. The static morphological traits of the wing also exhibit high phylogenetic signal whereas range of motion traits show greater evolutionary lability. Collectively, these results suggest a new framework for understanding the evolution of the vertebrate skeleton: rather than static morphology, it may be emergent properties such as range of motion that are predominantly reshaped as behaviors and body size evolve.
