The division between these two suborders represents a very deep evolutionary divide between two very different types of turtles.

The physical differences between them, although anatomical and largely internal, are nonetheless significant, and the zoogeographic implications of them are substantial.

[6] The Pleurodira turtles are currently restricted to freshwater habitats in the Southern Hemisphere, largely to Australia, South America, and Africa.

A larger overhang of the carapace helps to protect the neck, which remains partially exposed after retraction.

[10] These centra act as a double joint, allowing a large degree of sideways movement and providing a means of folding the neck onto itself in the lateral plane.

The biconvex centra in some of the cryptodiran cervicals allow the neck to fold onto itself in the vertical plane.