Cyprinodon

Cyprinodon is a genus of pupfishes found in waters that range from fresh to hypersaline. The genus is primarily found in Mexico, the Caribbean Islands and southern United States (Arizona, California, Florida, Nevada, New Mexico, Oklahoma and Texas), but C. variegatus occurs as far north as Massachusetts and along the entire Gulf of Mexico coastline, and C. dearborni and C. variegatus are found in northern South America. Many species have tiny ranges and are highly threatened, in some cases already extinct. Cyprinodon are small; the largest reaches 10 cm (3.9 in) in length and most other species only reach about half that size. Based on phylogenetic evidence, Cyprinodon diverged from its closest relative, the recently extinct Megupsilon, during the Late Miocene, and saw a rapid evolutionary radiation afterwards. The only known fossil species from the genus is C. breviradius from the late Miocene or early Pliocene-aged sediments of Death Valley National Park (originally considered part of the Late Eocene-aged Titus Canyon Formation). A few Cyprinodon species have quite large ranges, notably C. variegatus, but the vast majority have small ranges, typically restricted to one or two Mexican states or U.S. states, Hispaniola, or a Bahamian island. C. longidorsalis and C. diabolis have both been said to have the smallest native range of any vertebrate species, with the former being restricted to a spring pool that covers about 10 m (110 sq ft) and the latter to an 18 m (190 sq ft) shelf in a spring pool, but C. longidorsalis is now only found in captivity as its habitat has disappeared. While most Cyprinodon species have separate distributions, seven (C. beltrani, C. esconditus, C. labiosus, C. maya, C. simus, C. suavium and C. verecundus) are endemic in Lake Chichancanab in Quintana Roo, Mexico, and three (the endemic C. brontotheroides and C. desquamator, and the widespread C. variegatus) live in the hypersaline lakes on San Salvador Island in the Bahamas. In a few other cases separate species do come into contact towards the edges of their distributions where they often hybridize, notably C. eximius with C. pachycephalus and C. atrorus with C. bifasciatus, but also C. variegatus in places where it has been introduced by humans into the ranges of other Cyprinodon species.