Robust capuchin monkeys are capuchin monkeys in the genus Sapajus. Formerly, all capuchin monkeys were placed in the genus Cebus. Sapajus was erected in 2012 by Jessica Lynch Alfaro et al. to differentiate the robust (tufted) capuchin monkeys (formerly the C. apella group) from the gracile capuchin monkeys (formerly the C. capucinus group), which remain in Cebus.
Taxonomy
Based on the species and subspecies proposed by Groves in 2001 and 2005, robust capuchin monkey taxa include: Black-capped, brown or tufted capuchin, Sapajus apella Guiana brown capuchin, Sapajus apella apella Colombian brown capuchin, Sapajus apella fatuellus Margarita Island capuchin, Sapajus apella margaritae Large-headed capuchin, Sapajus apella macrocephalus Sapajus apella peruanus Sapajus apella tocantinus Blond capuchin, Sapajus flavius Black-striped capuchin, Sapajus libidinosus Sapajus libidinosus libidinosus Sapajus libidinosus pallidus Sapajus libidinosus juruanus Azaras's capuchin, Sapajus cay Black capuchin, Sapajus nigritus Sapajus nigritus nigritus Sapajus nigritus cucullatus Crested capuchin or robust tufted capuchin, Sapajus robustus Golden-bellied capuchin, Sapajus xanthosternos
S. flavius was only rediscovered in 2006. The specific species and subspecies within Sapajus are not universally agreed upon. For example, Silva (2001) proposed a slightly different species and subspecies split in which, for example Azara's capuchun, Sapajus libidinosus paraguayanus, is considered a separate species, Sapajus cay, as are the large-headed capuchin and the crested capuchin.
Taxonomic history
Philip Hershkovitz and William Charles Osman Hill published taxonomies of the capuchin monkeys in 1949 and 1960, respectively. These taxonomies included all robust capuchins, described then as the tufted group, in the single species Cebus apella, while three gracile (untufted) capuchin species were recognized. Over time, the original C. apella was split into the additional species of robust capuchin monkeys recognized today. In 2001, Silva published a study in which he found greater genetic diversity among robust capuchins than among gracile capuchins. Silva's study also concluded that due to the differences between robust and gracile capuchins, the two groups should at least be placed in separate subgenera within the genus Cebus, offering Sapajus as the subgenus name for robust capuchins. After further studies of the morphology and genetics of the capuchin monkeys, Lynch Alfaro, Silva and Rylands proposed elevating Sapajus to a separate genus in 2012.
Evolutionary history
The genetic studies led by Lynch Alfaro concluded that robust and gracile capuchin monkey genera diverged about 6.2 million years ago. This is approximately the same time that humans and chimpanzees are believed to have diverged. In contrast, capuchins diverged from their nearest common relative, squirrel monkeys, over 13 million years ago. Lynch Alfaro suggested that the formation of the Amazon River may have caused the split that led to separation of robust and gracile capuchins. The robust capuchins then evolved in the Atlantic forest, while the gracile capuchins evolved in the Amazon.
In the late Pleistocene, about 400,000 years ago, robust capuchins began to expand their range northwards into the Cerrado and the Amazon. In some of these areas robust capuchins outcompeted gracile capuchins, and are now the only capuchin monkeys in the area, while particularly in the north Amazon, robust capuchins are sympatric with gracile capuchins. In areas of sympatry, robust capuchins achieve higher population densities than gracile capuchins. This is thought to reflect the advantage of the adaptations for durophagy in the robust forms, which allow them to exploit hard nuts, palm fruit and unripe fruit, while gracile forms are more restricted to ripe fruit. In general, robust capuchins seem to be more flexible in their diet.