title: Walking like dinosaurs: chickens with artificial tails provide clues about non-avian theropod locomotion.
abstract: Birds still share many traits with their dinosaur ancestors, making them the best living group to reconstruct certain aspects of non-avian theropod biology. Bipedal, digitigrade locomotion and parasagittal hindlimb movement are some of those inherited traits. Living birds, however, maintain an unusually crouched hindlimb posture and locomotion powered by knee flexion, in contrast to the inferred primitive condition of non-avian theropods: more upright posture and limb movement powered by femur retraction. Such functional differences, which are associated with a gradual, anterior shift of the centre of mass in theropods along the bird line, make the use of extant birds to study non-avian theropod locomotion problematic. Here we show that, by experimentally manipulating the location of the centre of mass in living birds, it is possible to recreate limb posture and kinematics inferred for extinct bipedal dinosaurs. Chickens raised wearing artificial tails, and consequently with more posteriorly located centre of mass, showed a more vertical orientation of the femur during standing and increased femoral displacement during locomotion. Our results support the hypothesis that gradual changes in the location of the centre of mass resulted in more crouched hindlimb postures and a shift from hip-driven to knee-driven limb movements through theropod evolution. This study suggests that, through careful experimental manipulations during the growth phase of ontogeny, extant birds can potentially be used to gain important insights into previously unexplored aspects of bipedal non-avian theropod locomotion.
authors: Institute of Ecology and Biodiversity, Facultad de Ciencias, Universidad de Chile, Santiago, Chile ; Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors: Bruno
authors: B
authors: Grossi
authors: Department of Oral Biology, University of Illinois at Chicago, Chicago, Illinois, United States of America ; Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, United States of America.
authors: José
authors: J
authors: Iriarte-Díaz
authors: Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors: Omar
authors: O
authors: Larach
authors: Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors: Mauricio
authors: M
authors: Canals
authors: Institute of Ecology and Biodiversity, Facultad de Ciencias, Universidad de Chile, Santiago, Chile ; Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors: Rodrigo A
authors: RA
authors: Vásquez
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002645:Chickens / Q000033:anatomy & histology* / Q000502:physiology*; D025061:Dinosaurs / Q000033:anatomy & histology / Q000502:physiology*; D005121:Extremities / Q000033:anatomy & histology / Q000502:physiology; D008124:Locomotion; D011187:Posture; D016138:Walking