Forelimb dimensions and goniometry of the wrist and fingers in tufted capuchin monkeys (Cebus apella): Developmental and comparative aspects

Abstract

Adult capuchin monkeys use precision grips during manipulation of small objects, although their thumbs have been classified as pseudo-opposable. We investigated the physical properties of the hands to increase our understanding of manual function in capuchins. Forelimb dimensions and joint mobility (goniometric) measurements were obtained from adult, juvenile, and infant tufted capuchins (Cebus upella). Compared to adult squirrel monkeys, adult capuchins exhibited less flexibility of the wrist and digits. Capuchins of all ages had proportionally longer hands than squirrel monkeys, and capuchins more than 7 weeks old had proportionally longer thumbs than squirrel monkeys. Growth of the arms and hands was asynchronous. The duration of growth of the thumb was particularly prolonged, extending into early adulthood. Age-related changes in flexibility were apparent in most indices, and were greatest at the metacarpophalangeal joints. It is unknown to what extent the characteristics of growth, forelimb dimensions, and goniometry presented by capuchins are shared with other species, or if they contribute to the capuchin's unusual prehensive capacities. However, the marked differences between adult capuchins and squirrel monkeys in these metrics, and between capuchins and rhesus in the growth patterns of the digits, suggest that variation across taxa in these characteristics can be considerable.

Grasping primate development: Ontogeny of intrinsic hand and foot proportions in capuchin monkeys (Cebus albifrons and Sapajus apella)

“…On average, over the first three years of life manual phalangeal indices declined by approximately 11% from their initial values at birth (Table 3). Similarly, Fragaszy, Adams-Curtis, Baer, and Carlson- Lammers (1989) found that the external length of the third ray, relative to that of the palm, was greatest in neonatal S. apella and decreased into adulthood. Ontogenetic declines in phalangeal indices were similar across the two capuchin species, in spite of documented differences in foraging strategy between "gracile" capuchins (i.e., Cebus) and "robust" capuchins (i.e., Sapajus) (Alfaro et al, 2012).…”

“…On average, over the first three years of life manual phalangeal indices declined by approximately 11% from their initial values at birth (Table 3). Similarly, Fragaszy, Adams-Curtis, Baer, and Carlson- Lammers (1989) found that the external length of the third ray, relative to that of the palm, was greatest in neonatal S. apella and decreased into adulthood. By three years of age, mean capuchin phalangeal indices for the third manual ray (as a representative digit) was 139%, within the range of values published previously for other adult cebid monkeys (i.e., Saimiri: 145%; Saguinus:…”

“…Because infant monkeys cling to the carrier with both the hands and the feet (Fragaszy et al, 1989(Fragaszy et al, , 2004b, one might expect similar ontogenetic declines in relative digit lengths if grasping during passive transport were the primary function of relatively long digits early in life.…”

Hand use by tufted capuchins (Cebus apella) to extract a small food item from a tube: digit movements, hand preference, and performance

“…A rotational movement of the wrist and forearm toward the radial side of the hand was noted more often in association with power than with precision grips. Overall, these data indicate that capuchins possess a high flexibility of the carpal joints [Fragaszy et al, 1989] that allows them to execute radio/ulnar movements of the wrist during their dexterous prehensile activities. This pattern is well developed in macaque monkeys [Christel & Billard, 2002].…”

Compound grips in tufted capuchin monkeys (Sapajusspp andSapajus libidinosus)

“…Wooden balls (1.27 cm diameter) were presented. One ball was roughly one quarter the width of a capuchin's palm (Fragaszy, Adams‐Curtis, Baer, & Carlson‐Lammers, 1989). Balls were painted with acrylic paint (red, blue, yellow, green), and coated in polyurethane (Figure 2).…”