Jaw shape varies among species. Each species has a jaw shape adapted for its diet. The large, bony shell provides protection from predation and abrasion. In all species except the leatherback, the shell is covered with a layer of horny plates called scutes. Scutes are firm but flexible, not brittle.
Scientists can identify sea turtle species by the number and pattern of scutes.
The leatherback turtle has a thick and oil-suffused skin, which is an excellent insulator allowing this species to venture into colder waters. Depending on species, the adult carapace ranges in shape from oval to heart-shaped. In all species except the leatherback, the bony shell is composed of broadened, fused ribs, and the backbone is attached to the carapace. In all species except the leatherback, the backbone is attached to the carapace. The leatherback's carapace is composed largely of cartilage raised into prominent logitudinal ridges.