YOUNG, JW*; FERNANDEZ, D; Stony Brook University; Stony Brook University: Ontogeny of limb bone geometry and bone strength in an arboreal primate (Cebus albifrons)

In numerous mammalian taxa, limb bone cross-sectional dimensions tend to be relatively greater early in life and decrease with negative allometry over postnatal growth. Greater cross-sectional dimensions increase bone strength, allowing young mammals to maintain adequate safety factors in spite of reduced mineralization and more erratic locomotion. However, by focusing on primarily precocial and terrestrial taxa, previous studies have likely undersampled the full range of life history variables and locomotor behaviors that may influence long-bone growth in mammals. This study examined ontogenetic changes of limb bone cross-sectional properties in an arboreal primate, the white-fronted capuchin monkey (Cebus albifrons). As primates, capuchin monkeys are a relatively altricial taxon that moves and forages almost entirely an arboreal environment. Due to the three-dimensional nature of arboreal locomotion, loading regimes may be more varied and unpredictable than during terrestrial locomotion, perhaps necessitating different scaling patterns during postnatal growth. Cortical diameters, second moments of area and section moduli (a measure of bending strength) of the humerus and femur were measured in a longitudinal radiographic series of five male capuchin monkeys spanning the first five years of life. Relative to body mass, femoral dimensions scaled with significant positive allometry, differing from the trend observed in ontogenetic studies of other mammals. Humeral dimensions scaled isometrically. These data suggest that arboreality and terrestriality may exert contrasting pressures on long bone growth in mammals. Detailed studies of locomotor ontogeny in capuchin monkeys and other are required to further clarify the observed scaling patterns.