Meeting Abstract
Birds can use different types of gaits to move on the ground: they either walk, hop, or run. Although preference for running can easily be linked to velocity, it remains unclear what drives a bird to walk rather than to hop at moderate speeds. As it appears that many hopping birds are arboreal, we wanted to test an arboreal origin of hopping. To explore this question, we carried out ancestral character state reconstructions of both hopping ability and lifestyle on a wide diversity of Neotropical birds (N=96 species). Then, we quantified the morphological differences of the pelvis and the three long bones of the hindlimbs in 26 species of birds with different habitats and gait preferences. We used geometric morphometrics on 3D landmarks, digitized on micro-CT scans of the specimens. We found that hopping ability and arboreality were both derived traits in avian evolution and that the shape of the pelvis, femur, tibiotarsus, and tarsometatarsus carried a strong phylogenetical signal, reinforcing the importance of performing our analysis in a phylogenetical context. Our geometric morphometrics analysis revealed that the locomotion habits significantly influence the shape of the pelvis, femur and tibiotarsus, but not the shape of the tarsometatarsus: hopping birds tend to have a less elongated and broader pelvis than walking bird, with a straighter femur. These features may provide efficient propulsion and dampening of the forces involved in hopping and could confer a selective advantage to move in the trees. This work provides elements on a potential arboreal origin of hopping and on the evolution of avian locomotion, which could help us better understanding the evolution of theropod dinosaurs.
