The Kaapori capuchin (Cebus kaapori), also known as the Ka'apor capuchin, is a species of frugivorous, gracile capuchin endemic to the Brazilian Amazon. Their geographical home range is relatively small and is within the most densely populated region of the Amazon. With the strong human presence nearby,C. kaapori has had to deal with very large amounts of disturbances to their habitat and is one of the most endangered of the neotropical primates. Taxonomy First described by Helder Queiroz in 1992, C. kaapori was considered a subspecies for a long time. At the time of his discovery, Queiroz noted its similarities with the members of the C. olivaceus species. After analyzing their genetic makeup, researchers Harada and Ferrari argued that the Ka'apor capuchins should be considered a subspecies of the latter. However, due to various morphological and molecular evidence, the species is currently deemed a valid species in its own right. Physical characteristics Part of the genus of gracile capuchin monkeys, the ka'apor capuchin tend to have longer limbs in comparison to their body size as opposed to members of the Sapajus genus. On average, the adult male Ka'apor capuchin weighs approximately 3 kg. They also have rounder skulls as well as differences in their teeth and jaws which renders them incapable of opening hard nuts like their robust counterparts. Another notable trait is that no male gracile capuchin have tufts on their head, whereas all Sapajus do. Habitat and distribution The Ka'apor capuchin has been described as having one of the smallest geographical ranges of any other Cebus species in the Amazon. They can be found in the eastern border of the Brazilian Amazon along the Atlantic coast; more specifically in the states of Pará and Maranhão. The region is known as for having the highest population density in all of the Amazon. Due to the large human population living in the same area, the species tend to live in isolated patches of tall, lowland terra firme forest. Included in their range, are two protected stretches of land: the Gurupi Biological Reserve and the Lago de Turucuí Environmental Protection Area. Studies of the Ka'apor capuchin populations in these areas have had very varying results but the consensus seems to be that the species is quite rare, even within their known range. In one study, researchers following a group of C. kaapori observed that their average daily travel was of approximately