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ABSTRACT ObjectivesWild juvenile capuchins exhibit lower feeding success than adults, particularly for mechanically challenging foods, but ontogenetic changes in oral food processing behaviors related to this reduced success are unknown. We test how oral food processing efficiency varies across development in an experimental setting in tufted capuchins (Sapajusspp.). Further, we simulate discontinuous feeding observations to test the comparability of behaviors measured in wild and captive settings. Materials and MethodsTwenty‐nine captive and semi‐wild infants (n = 2), juveniles (n = 12), older juveniles (n = 4), and subadults‐adults (n = 11) were video recorded while feeding at the Núcleo de Procriação de Macacos‐Prego Research Center (Araçatuba, Brazil). Each animal was offered a series of five foods ranging in volume, toughness, and elastic modulus. ResultsMeasures of oral food processing inconsistently varied with sex; however, younger animals were less efficient in food processing than older individuals. Larger and more mechanically challenging foods were associated with longer feeding sequence durations and an increased frequency of anterior ingestion, posterior ingestion, and chewing during a feeding sequence. Simulated discontinuous data from the first and last halves of the feeding sequences closely replicated continuous results. ConclusionsOur results indicate younger capuchins have reduced oral food processing efficiency compared to adults through increased duration, behavioral frequencies, number of chews, and behavioral patterns. Further, our continuous and discontinuous comparisons support the use of discontinuous feeding behaviors from the first and last halves of the feeding sequence. We caution that researchers should be careful to capture infrequent behaviors when using discontinuous data. 

Abstract Skeletal muscle fibre architecture provides important insights into performance of vertebrate locomotor and feeding behaviours. Chemical digestion and in situ sectioning of muscle bellies along their lengths to expose fibres, fibre orientation and intramuscular tendon, are two classical methods for estimating architectural variables such as fibre length (L_f) and physiological cross‐sectional area (PCSA). It has recently been proposed thatL_festimates are systematically shorter and hence less accurate using in situ sectioning. Here we addressed this hypothesis by comparingL_festimates between the two methods for the superficial masseter and temporalis muscles in a sample of strepsirrhine and platyrrhine primates. Means or single‐specimenL_festimates using chemical digestion were greater in 17/32 comparisons (53.13%), indicating the probability of achieving longer fibres using chemical digestion is no greater than chance in these taxonomic samples. We further explored the impact of sampling on scaling ofL_fand PCSA in platyrrhines applying a bootstrapping approach. We found that sampling—both numbers of individuals within species and representation of species across the clade significantly influence scaling results ofL_fand PCSA in platyrrhines. We show that intraspecific and clade sampling strategies can account for differences between previously published platyrrhine scaling studies. We suggest that differences in these two methodological approaches to assessing muscle architecture are relatively less consequential when estimatingL_fand PCSA for comparative studies, whereas achieving more reliable estimates within species through larger samples and representation of the full clade space are important considerations in comparative studies of fibre architecture and scaling. 

Abstract ObjectivesCortical bone geometry is commonly used to investigate biomechanical properties of primate mandibles. However, the ontogeny of these properties is less understood. Here we investigate changes in cortical bone cross‐sectional properties throughout capuchin ontogeny and compare captive versus wild, semi‐provisioned groups. Tufted capuchins (Sapajusspp.) are known to consume relatively hard/tough foods, while untufted capuchins (Cebusspp.) exploit less mechanically challenging foods. Previous research indicates dietary differences are present early in development and adultSapajusmandibles can resist higher bending/shear/torsional loads. Materials and methodsThis study utilized microCT scans of 22Cebusand 45Sapajusfrom early infancy to adulthood from three sample populations: one captiveCebus, one captiveSapajus, and one semi‐provisioned, free‐rangingSapajus. Mandibular cross‐sectional properties were calculated at the symphysis, P₃, and M₁. If the tooth had not erupted, its position within the crypt was used. A series of one‐way ANOVAs were performed to assess differences between and within the sample populations. ResultsMandible robusticity increases across ontogeny for all three sample populations.Sapajuswere better able to withstand bending and torsional loading even early in ontogeny, but no difference in shear resistance was found. Semi‐provisioned, free‐rangingSapajustend to show increased abilities to resist bending and torsional loading but not shear loading compared to captiveSapajus. DiscussionThis study helps advance our understanding of the primate masticatory system development and opens the door for further studies into adaptive plasticity in shaping the masticatory apparatus of capuchins and differences in captive versus free‐ranging sample populations.