Central American Region

in zoogeography, the part of the Tropical Realm that encompasses the continental shelf in the tropical parts of the eastern Pacific and western Atlantic (including the Caribbean Sea and Gulf of Mexico), that is, the waters on both sides of the Isthmus of Panama. The region is sometimes classified as a subregion of the Tropical Region.

Besides genera that are common to the tropics and genera that are endemic to either the western or the eastern side of the isthmus, the region has many endemic genera, especially among fish, crabs, and echinoderms, which are found on both sides of the isthmus. Such genera, called amphi-American genera, are represented in the Pacific and Atlantic by related but different species. The waters of the western Atlantic and the eastern Pacific contain few of the same species: only about 1 percent of the shelf s fish and mollusk species and 1–10 percent of other invertebrate species are identical. Amphi-American forms are also found among the deep-sea (bathyal and abyssal) bottom animals. The pelagic faunas on the two sides of the isthmus are completely different; only circumtropical species are common to both sides. The am-phi-American areas are vestiges of past geological ages (Cretaceous-Paleogene), when the eastern Pacific and the Caribbean were connected by a strait that was completely closed up in the Pliocene, about 5 million years ago.

The Central American Region is divided into two subregions: the western Atlantic and the eastern Pacific. In view of the small number of identical species, many zoogeographers consider the Central American Region to be an artificial unit and treat the two subregions as independent regions. The western Atlantic waters have 1.5 times more species than those of the eastern Pacific and, unlike the latter, have extensively developed coral reefs with their typical fauna.