Scaling patterns of body plans differ among squirrel ecotypes

Body size is often hypothesized to facilitate or constrain morphological diversity in the cranial, appendicular, and axial skeletons. However, how overall body shape scales with body size (i.e., body shape allometry) and whether these scaling patterns differ between ecological groups remains poorly investigated. Here, we test whether and how the relationships between body shape, body size, and limb lengths differ among species with different locomotory specializations, and describe the underlying morphological components that contribute to body shape variation among squirrel (Sciuridae) ecotypes. We quantified the body size and shape of 87 squirrel species from osteological specimens held at museum collections. Using phylogenetic comparative methods on these data, we found that 1) body shape and its underlying morphological components scale allometrically with body size, but these allometric patterns differ among squirrel ecotypes; 2) only ground squirrels exhibit a relationship between forelimb length and body shape, where more elongate species exhibit relatively shorter forelimbs; and 3) the relative length of the ribs and elongation or shortening of the thoracic region contributes the most to body shape variation across squirrels. Overall, our work contributes to the growing understanding of mammalian body shape evolution and how it is influenced by body size and locomotor ecology, in this case from robust subterranean to gracile gliding squirrels.