South America supports an extremely diverse assemblage of side-necked turtles. The two distinct families, 12 genera and 30 species represent aquatic and semiaquatic turtles that dwell in rivers, lakes and marshes, temporary pools in savannas, and leaf litter of jungle floors. They range in size from the giant 3-foot-long, 200-pound Amazon River turtle (Podocnemis expansa) to the 6-inch-long twist-necked turtle (Platemys platycephala) and gibba turtle (Mesoclemmys [Phrynops] gibba). This mix includes many plain-Jane species as well as the bizarre matamata (Chelus fimbriata). Males are generally smaller than females. In some species this size difference is as great as 30 percent.
For the most part, these turtles are tropical species occurring primarily in the Amazon and Orinoco river basins. All are restricted to areas east of the Andes, and none are found in Central America. Several live near the Atlantic coast as far south as Uruguay and Argentina. Although some have limited distributions, many range widely through the South American tropics. The closest living relatives of the South American side-necks are in Africa, Madagascar and Australia.
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