Podocnemididae is a family of pleurodire turtles native to Madagascar and northern South America. Podocnemidid turtles are commonly called "side-necked turtles" in direct reference to their inability to retract their heads backwards, but hide them sideways. In addition, their pelvis is fused to the shell which prevents any pelvic motion. Due to their pelvis being immobile they are unable to walk on land, which requires greater pelvis mobility. For this reason, Podocnemididae turtles are best suited for swimming and as a result live in aquatic environments. These turtles are all aquatic, inhabiting streams and other flowing water. Their shells are streamlined to aid in swimming.