any other squirrel monkey species. A study of nuclear and mitochondrial DNA demonstrated that the Central American squirrel monkey is indeed a separate species that apparently diverged from the South American species long ago – at least 260,000 years ago and possibly more than 4 million years ago. A genetic study by Lynch Alfaro, et al. in 2015 estimated that the Central American squirrel monkey diverged from S. scuireus a little less than 1 million years ago. One popular theory is that squirrel monkeys did live in Colombia during the late Miocene or Pliocene and these squirrel monkeys migrated to Central America, becoming the ancestors of the current Central American species. According to this theory, the Guatemalan black howler migrated to Central America around the same time. Passage through the isthmus of Panama later closed due to rising oceans, and eventually opened up to another wave of migration about 2 million years ago. These later migrants, ancestors to modern populations of white-headed capuchins, mantled howlers and Geoffroy's spider monkeys, out-competed the earlier migrants, leading to the small range of the Central American squirrel monkey and Guatemalan black howler. Ford suggested that high water levels during the Pleistocene not only cut off the Central American squirrel monkey from other squirrel monkeys, but was also responsible for the formation of two subspecies. Lynch Alfaro, et al. suggested that the separation of the Central American squirrel monkey from other squirrel monkeys may have resulted from a period of high aridity in northern South America. The population density has been estimated at 36 monkeys per square kilometer (93 per square mile) in Costa Rica and 130 monkeys per square kilometer (337 per square mile) in Panama. It has been estimated that the population of the Central American squirrel monkey has been reduced from about 200,000 in the 1970s to less than 5,000. This is believed to be largely due to deforestation, hunting, and capture for the pet trade. There are significant efforts within Costa Rica to try to preserve this monkey from extinction. A reforestation project within Panama tries to preserve the vanishing population of the Chiriqui Province. As of 2021, the Central American squirrel monkey is listed as endangered from a conservation standpoint by the IUCN. This is due mainly to deforestation ongoing habitat loss, but other sources such as capture for the pet trade also contribute. References External links ARKive – images