This sideneck turtle family contains about 11 genera and 52 species distributed in Tropical America and Australia and New Guinea. Chelid turtles appear to have shared an ancestor with the Pelomedusidae, side-neck turtles from Africa and South America. They are mostly carnivorous, aquatic and semi-aquatic in freshwater, but a few may enter brackish water, and at least two species survive long periods of drought buried in mud. Their egg shells are brittle. Their carapace size ranges from 150-500 mm. Pritchard and Trebbau (1984, The Turtles of Venezuela) hypothesized a trans-Antarctic distribution to explain the current distribution of these turtles. They wrote:
"Despite its poor fossil record, the family Chelidae is known from deposits as early as the Eocene. The fact that the Eocene forms are relatively advanced suggests that the family was already differentiated before the close of the Mesozoic, at which time the Antarctic is known to have had a relatively moderate climate.... The shift of the Antarctic continent to its present polar position took place during the early and mid-tertiary, during which time the deteriorating climate displaced almost all of the biota."
The Matamata Turtle, Chelus fimbriata (Schneider, 1783). Photographs of captive specimens. The matamata turtle is perhaps the world's most unusual turtle. It inhabits the Orinoco and Amazon River basins of South America, and it may occur as an established population on Trinidad. This turtle is almost entirely aquatic. Food is obtained using a sit and wait strategy, but fish herding has also been reported. Chelus opens its mouth explosively, creating a vacuum and sucking in prey. This turtle often inhabits turbid water and it is likely that prey is detected from the vibrations produced by the prey. Matamatas have tiny eyes, but can feed in the dark. While it is mostly freshwater, one specimen was reported with dead barnacles on its carapace, suggesting it spent some time in salt water. Adults can reach 450 mm in carapace length.
A sideneck turtle in the genus Chelodina. Captive animals of unknown origins. Some of the turtles in the genus Chelodina have exceptionally long necks (see below), some have necks that are longer than the carapace. The genus contains at least 8 species, probably more. Chelodina are semi-aquatic chelonians that are omnivorous. They are endemic to the Australia-New Guinea region. These turtles are also called snakenecked turtles or longnecked turtles.
