Associations between Skeletal Fractures and Locomotor Behavior, Habitat Use, and Body Mass in Nonhuman Primates

Injuries sustained during falls from heights may be the most frequent cause of long bone trauma among nonhuman primates. Yet the interrelatedness of trauma and positional behaviors is poorly understood. The purpose of this study is to assess how common locomotor behaviors, broad habitat use tendencies, and body mass are associated with skeletal fracture frequencies in primates. Primates exhibiting a higher degree of arboreality should exhibit greater fracture frequencies than more terrestrial primates due to their greater risk of obtaining injuries in falls from heights. Similarly, primates whose locomotor repertoire includes more specialized behaviors should exhibit higher frequencies than those of more generalized quadrupeds. Falls sustained by primates commonly active higher in the canopy and larger primates should be more likely to show severe repercussions (as depicted by higher fracture frequencies) than primates active closer to the ground and smaller primates.;Fractured long bones from primates encompassing twenty-two taxonomic groups housed at The Ohio State University, Cleveland Museum of Natural History, American Museum of Natural History, National Museum of Natural History, and the Caribbean Primate Research Center were examined macroscopically and radiographically. Locomotor and habitat use profiles for each taxonomic group were developed based upon quantitative field observations in the primatological literature.;Fracture patterns appear to be most closely associated with locomotor mode, followed by arboreality, vertical distribution, and body mass, although each of these variables are interconnected. Locomotor mode preferences strongly correlate with fracture frequencies. As expected, suspensory primates exhibit the highest fracture frequencies, although leapers have the lowest frequencies. The locations of fractures are significantly correlated with some aspect of every variable examined. When suspensory primates break a bone, it tends to be either the humerus or femur. Small- or medium-sized, arboreal quadrupeds are more likely to fracture their tibia or fibula than another long bone, whereas large and very large quadrupeds tend to fracture any long bone preferentially except for the tibia or fibula. Fracture occurrences in leaping primates tend either to involve the clavicle preferentially or are independent of location. Factors contributing to intraspecific variation in fracture frequencies, including the impact of sex, age, and changing population pressures, may contribute to differential fracture distributions. Combining skeletal samples with behavioral observations from individuals' life histories highlights the under-representation of fractures in field studies as well as over-estimates of the degree to which fractures impair mobility.;The fact that fracture frequencies and patterns revealed in this study are associated with locomotor and positional behaviors appears to highlight the importance of risk avoidance in primate evolution. Skeletal trauma may affect reproductive fitness either directly or incidentally. Consequently, primates should be under selective pressure to avoid the risk of obtaining fractures, developing behavioral and anatomical mechanisms to reduce the number and severity of falls from heights. Further analyses of the anatomical distribution of fractures in primates may reveal selective factors shaping locomotor anatomy. Ultimately, the analysis of fractures in primates which have healed under natural conditions may lead to a greater understanding of the origins of medical intervention in humans.