Bone volume in the distal calcaneus correlates with body size but not leap frequency in galagids.

OBJECTIVES: Primate leap performance varies with body size, where performance will be optimized in lightweight individuals due to the inverse relationship between force generation and body mass. With all other factors equal, it is less energetically costly to swing a light hindlimb than a heavier hindlimb. Previous work on the calcaneus of galagids hypothesized that bone volume in leaping galagids may be minimized to decrease overall hindlimb mass. We predict that (1) lighter taxa will exhibit relatively less calcaneal bone volume than heavier taxa, and (2) taxa that are high-frequency leapers will exhibit relatively less bone volume than lower frequency leapers. MATERIALS AND METHODS: Relationships among bone volume, body size, and leap frequency (high vs. low) were examined in a sample of 51 individuals from four genera of galagids (Euoticus, Galago, Galagoides, and Otolemur) that differ in the percentage of time engaged in leaping locomotion. Using µCT scans of calcanei, we quantified relative bone volume (BV/TV) of the distal calcaneal segment and predicted that it would vary with body size and frequency of leaping locomotion. RESULTS: Phylogenetic generalized least squares (PGLS) regression models indicate that body size, but not leaping frequency, affects BV/TV in the distal calcaneus. Relative bone volume increases with body size, supporting our first hypothesis. DISCUSSION: These results support previous work demonstrating a positive correlation between BV/TV and body size. With some exceptions, small galagids tend to have less BV/TV than larger galagids. Leaping frequency does not relate to BV/TV in this sample; larger taxonomic and/or behavioral sampling may provide additional insights.

The effects of phylogeny, body size, and locomotor behavior on the three-dimensional shape of the pelvis in extant carnivorans.

The mammalian pelvis is thought to exhibit adaptations to the functional demands of locomotor behaviors. Previous work in primates has identified form-function relationships between pelvic shape and locomotor behavior; few studies have documented such relationships in carnivorans, instead focusing on long bones. Most work on the functional morphology of the carnivoran pelvis, in particular, has used univariate measures, with only a few previous studies incorporating a three-dimensional (3D) analysis. Here we test the hypothesis that carnivoran taxa that are characterized by different locomotor modes also differ in 3D shape of the os coxae. Using 3D geometric morphometrics and phylogenetic comparative methods, we evaluate the phylogenetic, functional, and size-related effects on 3D pelvis shape in a sample of 33 species of carnivorans. Using surface models derived from laser scans, we collected a suite of landmarks (N = 24) and curve semilandmarks (N = 147). Principal component analysis on Procrustes coordinates demonstrates patterns of shape change in the ischiopubis and ilium likely related to allometry. Phylogenetic generalized least squares analysis on principal component scores demonstrates that phylogeny and body size have greater effects on pelvic shape than locomotor function. Our results corroborate recent research finding little evidence of locomotor specialization in the pelvis of carnivorans. More research on pelvic morphological integration and evolvability is necessary to understand the factors driving pelvic evolution in carnivorans.