Cebus aequatorialis
Cebus albifrons
Cebus brunneus
Cebus capucinus
Cebus castaneus
Cebus cesare
Cebus cuscinus
Cebus imitator
Cebus kaapori
Cebus leucocephalus
Cebus malitiosus
Cebus olivaceus
Cebus trinitatis
Cebus unicolor
Cebus versicolor
Cebus yuracus
Gracile capuchin monkeys are capuchin monkeys in the genus Cebus. At one time all capuchin monkeys were included within the genus Cebus. In 2011, Jessica Lynch Alfaro et al. proposed splitting the genus between the robust capuchin monkeys, such as the tufted capuchin, and the gracile capuchins.[1] The gracile capuchins retain the genus name Cebus, while the robust species have been transferred to Sapajus.[1][3]
The placement of the Trinidad white-fronted capuchin is controversial; the American Society of Mammalogists classifies it as conspecific with C. brunneus based on a 2012 study later found to be flawed, while the IUCN Red List classifies it as a distinct species (Cebus triniatis) due to debate over the aforementioned study, and the ITIS classifies it as a subspecies of C. albifrons, also due to debate over the aforementioned study.[6][7][8][9]
Philip Hershkovitz and William Charles Osman Hill published taxonomies of the capuchin monkeys in 1949 and 1960, respectively.[1] These taxonomies established four species of capuchin monkey in the genus Cebus. One of those species, Cebus apella, is a robust capuchin and is now included in the genus Sapajus. The other three Cebus species included in that taxonomy were the gracile capuchin species Cebus albifrons, Cebus nigrivittatus and the type species Cebus capucinus.[3] Cebus nigrivittatus was subsequently renamed Cebus olivaceus.[3][10] Cebus kaapori had been considered a subspecies of C. olivaceus but Groves (2001 and 2005) and Silva (2001) regarded it as a separate species.[11]
The gracile capuchins, like all capuchins, are members of the family Cebidae, which also includes the squirrel monkeys. The evolution of the squirrel monkeys and capuchin monkeys is believed to have diverged about 13 million years ago.[1] According to genetic studies led by Lynch Alfaro in 2011, the gracile and robust capuchins diverged approximately 6.2 million years ago.[1][3] Lynch Alfaro suspects that the divergence was triggered by the creation of the Amazon River, which separated the monkeys in the Amazon north of the Amazon River, which evolved into the gracile capuchins, from those in the Atlantic Forest south of the river, which evolved into the robust capuchins.[1][3]
Gracile capuchins have longer limbs relative to their body size compared with robust capuchins.[1] Gracile capuchins also have rounder skulls and other differences in skull morphology.[1] Gracile capuchins lack certain adaptations for opening hard nuts which robust capuchins have.[1] These include differences in the teeth and jaws, and the lack of a sagittal crest.[1] Exterior differences include the fact that, although some females have tufts on their head (Humboldt's white-fronted capuchin and Guianan weeper capuchin), no male gracile capuchin has tufts, while all robust capuchins have tufts.[1] Also, no gracile capuchins have beards.[1]