Most geographically restricted family of snakes

The most geographically restricted family of snakes is Bolyeriidae, whose two species have been restricted entirely in modern times to Round Island – an uninhabited islet 22.5 km north of Mauritius in the Indian Ocean, with an area of only 1.69 square km. The two species are the Round Island keel-scaled ground boa Casarea dussumieri, and the Round Island burrowing boa Bolyeria multocarinata, which was last seen in 1975 and is now believed to be extinct. To save C. dussumieri from extinction too, it has been bred in captivity and introduced onto the nearby island of Gunner's Quoin.