Geomorph

For each individual we first recorded the 3D coordinates of 29 anatomical landmarks on each scapula surface model (Supplemental S1). These landmarks were chosen to capture the shape of the body, glenoid, spine, acromion, and coracoid process and are based on standards in comparative morphology (Young, 2004 ; Young, 2006 (link); Young et al., 2015 (link)). The landmarks were placed by a single user using a semiautomated user-directed method in the software Landmark Editor 3.6 (IDAV, Davis, CA, USA). Shape was quantified using three-dimensional geometric morphometrics (Zelditch et al., 2012 ). First, the raw 3D coordinates for each scapula were aligned and scaled to a common centroid size and rotated to minimize distance via generalized Procrustes superimposition as implemented in the R statistical software package geomorph (R Foundation for Statistical Computing, Vienna, Austria). We further tested for and removed the effects of allometry (size:shape relationships) by regressing against centroid size and utilizing the computed residuals.