A unique and diverse albeit phylogenetically restricted mammal fauna[note 1] is known from the Caribbean region. The region—specifically, all islands in the Caribbean Sea (except for small islets close to the continental mainland) and the Bahamas, Turks and Caicos Islands, and Barbados, which are not in the Caribbean Sea but biogeographically belong to the same Caribbean bioregion—has been home to several families found nowhere else, but much of this diversity is now extinct.
The bat faunas of much of the Caribbean show similarities that led to the proposal of a distinct Caribbean faunal region, bounded by "Koopman's Line". This region excludes several of the region's islands, including the Grenadines, Grenada, Trinidad, Tobago, and other islands near the American mainland, such as Margarita, Isla Escudo de Veraguas, Rosario Islands, Cozumel, and the Florida Keys.[1] The faunas of islands outside Koopman's Line are similar to those of the adjacent mainland, though usually smaller; in contrast, the region inside Koopman's Line harbors relatively few species shared with the mainland and many of its species belong to endemic genera, subfamilies, and even families.
Excluding bats, nearly 90% of the mammals of the Caribbean faunal region have gone extinct since the late Pleistocene,[2] including all the sloths and monkeys, the unique insectivore Nesophontes, two of four species of solenodon, and a variety of rodents including all giant hutias, leaving only a few hutia species extant.[3] Most of these species (the sloths, monkeys, and caviomorph rodents) were of South American origin. The oryzomyine rodents were of ultimately of Nearctic origin, but except for those on Jamaica would also have reached the Caribbean via South America. The origin(s) of the Caribbean eulipotyphlans are uncertain.[4]
Non-flying mammals of Cenozoic origin must have colonized the Caribbean islands by some combination of rafting and/or use of a "land span" (a temporary land bridge connecting South America with one or more off-shelf islands).[5][6][7] Colonization of a series of islands can occur either by an iterative rafting process ("island-hopping"), or by colonization of a large ancestral island which is then subdivided by into smaller islands by subsequent geologic or sea level changes (island-island vicariance).[8] The restricted, unbalanced nature of the Caribbean mammal fauna implies that rafting was part of the overall process.[6][7] This is consistent with the fact that megalonychid sloths, platyrrhine monkeys and caviomorph rodents have all shown a capacity for this type of dispersal (in their colonization of North America from South America prior to the formation of the Isthmus of Panama in the first case, and of South America from Africa in latter two cases). These three groups are known in the Caribbean from fossils as old as the early Oligocene, early Miocene and early Miocene, respectively. Rafting is also consistent with the prevailing flow of oceanic currents from South America towards the islands.[7]
The large proportion of extinctions can be attributed to the isolated and therefore somewhat less competitive nature of the islands' ecosystems, and to the fact that carnivorans never colonized most of the region. These factors made the islands' native fauna particularly vulnerable to disruption by humans[9] and the invasive species they introduced. The large predator niches of the Caribbean islands were formerly occupied by endemic outsize hawks, falcons, caracaras, teratorns and owls, such as Titanohierax, Gigantohierax, Buteogallus borrasi, Caracara tellustris, Oscaravis olsoni, Ornimegalonyx and Tyto pollens - all of which are now extinct. Cuban crocodiles also have more terrestrial habits than other extant crocodilians.
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