Anatomical Analysis of Thumb Opponency Movement in the Capuchin Monkey (Sapajus sp)

Abstract

Capuchin monkeys present a wide variety of manipulatory skills and make routine use of tools both in captivity and in the wild. Efficient handling of objects in this genus has led several investigators to assume near-human thumb movements despite the lack of anatomical studies. Here we perform an anatomical analysis of muscles and bones in the capuchin hand. Trapezo-metacarpal joint surfaces observed in capuchins indicate that medial rotation of metacarpal I is either absent or very limited. Overall, bone structural arrangement and thumb position relative to the other digits and the hand’s palm suggest that capuchins are unable to perform any kind of thumb opponency, but rather a ‘lateral pinch’ movement. Although the capuchin hand apparatus bears other features necessary for complex tool use, the lack thumb opposition movements suggests that a developed cognitive and motor nervous system may be even more important for high manipulatory skills than traditionally held.

Anatomia comparativa dos nervos da pelve de macacos-prego (Sapajus sp)

“…When the anatomical data are applied to evolutionary, taxonomy and phylogenetic studies, errors could be propagated indefinitely and incorrect conclusions and hypothesis will be obtained (AVERSI-FERREIRA et al, 2014a).…”

“…On the other hand, anatomical structures of bearded capuchins seem to be closer to those of other New World primates, per its taxonomy, but few studies on its anatomy are reported (AVERSI-FERREIRA et al, 2014a). Nevertheless, in recent years some, but not enough, works about Sapajus anatomy associated with its behavioral aspects were performed.…”

“…Bearded capuchins (Sapajus sp), unexpectedly, share with chimpanzees (Pan) various behavioral features such as high cognitive ability, good memory, tool use with intermittent bipedalism, and social tolerance (ANTINUCCI; VISALBERGHI, 1986;BOESCH;BOESCH, 1990;PHILLIPS, 1998;RYLANDS et al, 2000;TOMAZ, 2002;FRAGASZY et al, 2004;LOPES, 2004;VISALBERGHI et al, 2007;SABBATINI et al, 2008;DEFLER, 2009;MANNU;OTTONI, 2009;DEMES, 2011;DEMES;O´NEILL, 2012 however, their anatomical structures are like those of baboons (AVERSI-FERREIRA et al, 2005, 2010, 2011a, 2011b, 2013, 2014a, 2014b.…”

“…Then, the anatomical similarity to baboons (Papio) was studied (AVERSI-FERREIRA et al, 2005, 2010, 2011a, 2011b, 2013, 2014a, 2014b, inter alia, because the anatomical descriptions of the apes and baboons are easily found in previous literature, which are lacking in the New World primates.…”

“…World primates (AVERSI-FERREIRA et al, 2005, 2010, 2011a, 2011b, 2013, 2014a, 2014bSPAGNOLETTI et al, 2011). Indeed, the taxonomy of the bearded capuchins has been a source of discussion since the 18 th century in relation to correct names of the species (ERXLEBEN, 1777;SABBATINI et al, 2008) and recently, the genus was changed; for instance, the Sapajus genus was previously called…”