North American box turtles are turtles of the genus Terrapene. Although box turtles are superficially similar to tortoises in terrestrial habits and overall appearance, they are actually members of the American pond turtle family (Emydidae). The 12 taxa which are distinguished in the genus are distributed over seven species. They are largely characterized by having a domed shell which is hinged at the bottom, allowing the animal to retract its head and legs and close its shell tightly to protect itself from predators. Taxonomy and genetics The genus name Terrapene was coined by Blasius Merrem in 1820 as a genus separate from Emys, describing those species which had a sternum separated into two or three divisions, and which could move these parts independently. He placed in this genus, among others, Terrapene boscii (now accepted to be Kinosternon subrubrum subrubrum) and Terrapene carolina (but under the name Terrapene clausa). Also several Asian box turtles have been formerly classified within the genus Terrapene; e.g., Terrapene bicolor (now Cuora amboinensis couro) and Terrapene culturalia (now Cuora flavomarginata). Currently, six species are classified within the genus and 12 taxa are distinguished: Common box turtle, Terrapene carolina (Linnaeus, 1758) (type species) Florida box turtle, Terrapene carolina bauri Taylor, 1895 Eastern box turtle, Terrapene carolina carolina (Linnaeus, 1758) Gulf Coast box turtle, Terrapene carolina major (Agassiz, 1857) Terrapene carolina putnami O.P. Hay, 1906 (extinct) Three-toed box turtle, Terrapene triunguis (Agassiz, 1857) Coahuilan box turtle, Terrapene coahuila Schmidt & Owens, 1944 Mexican box turtle, Terrapene mexicana (Gray, 1849) Spotted box turtle, Terrapene nelsoni Stejneger, 1925 Northern spotted box turtle, Terrapene nelsoni klauberi Bogert, 1943 Southern spotted box turtle, Terrapene nelsoni nelsoni Stejneger, 1925 Western box turtle, Terrapene ornata, (Agassiz, 1857) Ornate box turtle, Terrapene ornata ornata (Agassiz, 1857) Desert box turtle, Terrapene ornata luteola H.M. Smith & Ramsey, 1952 Yucatán box turtle, Terrapene yucatana (Boulenger, 1895) Box turtles have diploid somatic cells with 50 chromosomes. Ecology and behavior Life cycle and predation Once maturity is reached, the chance of death seems not to increase with age. The survivorship curve of box turtles is therefore probably similar to that of other long-living turtles. The average life span of adult box turtles is 50 years, while a significant portion lives over 100 years. The age of a growing box turtle in the wild cannot be accurately estimated by counting the growth rings on the scutes; Their growth is directly