Pleurodire

Pleurodire is a major infraorder of turtles, commonly known as side-necked turtles. This group is distinguished by its unique method of retracting its head into its shell. Instead of pulling its head straight back, a pleurodire bends its neck sideways, tucking its head into the space between its upper arm and shoulder. This contrasts with the Cryptodira, or hidden-necked turtles, which pull their heads directly backward.

Pleurodires are found primarily in the Southern Hemisphere, with their distribution spanning South America, Africa, Australia, and New Guinea. They inhabit a variety of freshwater environments, including rivers, lakes, swamps, and marshes. Their diets are typically carnivorous, consisting of fish, insects, crustaceans, and amphibians, though some species may also consume plant matter.

The infraorder is divided into three extant families: Chelidae, Pelomedusidae, and Podocnemididae. Chelidae, the Australian side-necked turtles, are found in South America and Australia. Pelomedusidae, the African mud turtles, are exclusively found in Africa. Podocnemididae, the South American side-necked turtles, are restricted to South America and Madagascar.

Fossil evidence suggests that pleurodires have a long evolutionary history, with their origins dating back to the Cretaceous period. Their unique head-retraction mechanism is believed to be an adaptation to their specific ecological niches and predator avoidance strategies.