What is Chelidae?
{{Automatic taxobox | image = Chelus fimbriatus 2005.jpg | image_caption = ''[[Mata mata|Chelus fimbriatus]]'' | fossil_range = {{fossil_range|Albian|Recent}} | taxon = Chelidae | authority = [[John Edward Gray|Gray]], 1831 | subdivision_ranks = Genera | subdivision = See text. }} The '''Chelidae''' are a [[family (biology)|family]] of [[freshwater]] [[turtles]]. They are [[Pleurodira|''side-necked turtles'']]. The family is distributed in [[Australia]], [[New Guinea]], parts of [[Indonesia]], and throughout most of [[South America]]. It is a large family of turtles, and its fossil history goes back to the [[Cretaceous]]. The family Chelidae has about 60 living species in about twenty genera.<ref name=GBS>Georges, A. ''et al'' 1998. A phylogeny for side-necked turtles (Chelonia: Pleurodira) based on mitochondrial and nuclear gene sequence variation. ''Biological Journal of the Linnean Society'' '''67''': 213-246.</ref> The family is entirely [[Gondwana]]n in origin, with no members found outside Gondwana, either now or as a fossil.<ref name=GT>Georges A. & Thomson S. 2006. Evolution and zoogeography of Australian freshwater turtles. In: Merrick J.R. ''et al'' (eds) ''Evolution and zoogeography of Australasian vertebrates''. Sydney: Australia.</ref> They are called side-necked turtles because they withdraw their heads by moving the head sideways (see [[Pleurodira]]). Other turtles, if they withdraw their heads, pull them back in the vertical plane. The subfamilies within Chelidae show that most of the South American species and all the Australian species are a [[clade]], that is, evolved from the same ancestor ([[monophyly]]. The far more ancient turtle [[genus]] ''Hydromedusa'' is their [[sister taxon]].<ref name=prit84>Pritchard P.C.H. 1984. Piscivory in turtles, and evolution of the long-necked Chelidae. in Ferguson M.W. (ed) ''The structure, development and evolution of reptiles''. Zoological Society of London, Symposium. '''52''':87-110.</ref><ref name=sedd97>Seddon J. ''et al'' 1997. Phylogenetic relat