Evolution and systematics

The Acrochordidae, called wart snakes or file snakes, is an unusual family of strictly aquatic snakes consisting of a single genus and three species. The little file snake (Acrochordus gran-ulatus) is the smallest of the three species and has a largely marine distribution. It originally was thought to be venomous and was placed in a separate genus (Chersydrus). It seems best to include this species in the genus Acrochordus, although some systematists have maintained the two separate genera. The Arafura file snake (A. arafurae) and the Java file snake (A. ja-vanicus) are roughly twice the size of the little file snake and are largely freshwater in distribution. A fourth extinct species is known that existed in the Upper Miocene and Lower Pliocene epochs of Pakistan.

The phylogenetic relationships between acrochordids and other snakes are unclear. The snakes in this family retain some primitive characteristics but have evolved numerous specialized traits. Some morphologic features are so different from those of other snakes that file snakes have been joined in a separate superfamily, the Acrochordoidea. They appear to be related most closely to advanced snakes: colubrids (a large family including many common and familiar snakes such as garter snakes, rat snakes, and king snakes), elapids (cobras and their relatives), viperids (vipers and pit vipers), and a group of African snakes known as Atractaspididae.

Taxonomy for these species: Acrochordus arafurae McDowell, 1979, Papua New Guinea, Western Province, Lake Daviumbo; commonly known as the Arafura file snake. Acrochordus granula-tus Schneider, 1799, "India"; commonly known as the little file snake. Acrochordus javanicus Hornstedt, 1787, Java; commonly known as the Java file snake, wart snake, or elephant trunk snake.

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