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The World's Other Sea Turtles
Six species, one shared story — leatherback covered separately

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What Makes a Sea Turtle a Sea Turtle

Sea turtles are reptiles, the same class of animal as lizards, snakes, and crocodiles. Like all reptiles, they’re vertebrates, and their most recognizable trait is the shell: a domed carapace on top and a flatter plastron underneath, protecting the organs in between. Sea turtles are also ectothermic, or cold-blooded, meaning they can’t generate their own body heat internally the way mammals and birds do. Instead, their body temperature simply matches their surroundings, which is why they’re drawn to warm currents and tropical or subtropical waters, and why cold water can leave them sluggish or in trouble. (The leatherback is the one exception in the whole group, capable of holding its body warmer than the surrounding water.)

Sea turtles evolved from land-and-freshwater-dwelling ancestors roughly 100 million years ago, and their bodies still show that history at every turn. Ordinary land turtles can pull their head and legs into their shell for protection; sea turtles gave up that ability entirely in exchange for a more streamlined shell and long, paddle-shaped flippers, built for fast, sustained swimming across open ocean rather than for hiding. But one piece of their land ancestry never changed: sea turtles still breathe air with lungs, not gills, and as reptiles their eggs need to develop on land, buried in warm sand where oxygen can reach them, not underwater. That single constraint is why every sea turtle alive, no matter how much of its life is spent far out at sea, is still tied to a beach: females have to leave the water and haul themselves onto land to nest, generally returning to the very beach where they themselves hatched.

Green Turtle (Chelonia mydas)

The only sea turtle that is primarily herbivorous as an adult, grazing on seagrasses and algae, a diet that tints their body fat green and gives the species its name. Adults can reach 5 feet in length and 500 lbs, and the largest nesting colony in the Western Hemisphere is just up the coast at Tortuguero, Costa Rica, one of few sea turtle populations trending upward despite ongoing illegal harvest for meat and eggs. A smaller, darker form found in the Eastern Pacific, sometimes called the black sea turtle, nests mainly in Mexico and the Galápagos and has declined sharply over recent decades. Listed as Endangered by the IUCN.

Hawksbill (Eretmochelys imbricata)

Named for a narrow, beak-like jaw built for reaching into reef crevices, where it feeds on sponges, anemones, and other invertebrates most other species can’t access. Its strikingly patterned, overlapping shell scutes are also exactly what made it a historic target for the tortoiseshell trade, and illegal shell, meat, and egg collection remain active threats. Smaller than the green turtle, at around 2 to 3 feet and 130 lbs, and listed as Critically Endangered by the IUCN.

Olive Ridley (Lepidochelys olivacea)

One of only two species in the world known for synchronized mass nesting events called arribadas, in which tens or even hundreds of thousands of females come ashore together over a few nights. Costa Rica’s Pacific coast hosts some of the most significant arribada beaches anywhere, including Ostional and Nancite. At around 1.5 to 2 feet long and 75 to 100 lbs, it’s one of the smallest sea turtle species. Despite being the most abundant sea turtle species in the Eastern Pacific, heavy fisheries bycatch and egg harvest keep it listed as Endangered by the IUCN.

Loggerhead (Caretta caretta)

Named for its oversized head and powerful jaw muscles, built for crushing hard-shelled prey like crabs, clams, and mussels. Adults reach around 3.5 feet and up to 400 lbs. Loggerheads range across temperate and subtropical waters of the Pacific, Indian, and Atlantic Oceans, with major nesting concentrations along the southeastern United States and scattered sites around the Mediterranean; very few nest anywhere in Central America. Listed as Endangered by the IUCN.

Kemp's Ridley (Lepidochelys kempii)

The world’s rarest sea turtle, and, like its olive ridley relative, a mass-nester, though its arribadas happen almost exclusively on a single stretch of Mexican Gulf coast. It’s similarly small, around 2 feet long and 75 to 100 lbs, and feeds mostly on crabs. Found only in the Gulf of Mexico and adjacent Atlantic waters, it’s listed as Critically Endangered, but decades of nest protection combined with turtle excluder devices (TEDs) in shrimp fisheries have helped its numbers climb over the last decade, one of the clearer conservation success stories among sea turtles.

Flatback (Natator depressus)

The only sea turtle species confined to a single country, nesting and foraging exclusively in the waters of Australia. Named for its notably flat shell, it reaches close to 3 feet in length and roughly 200 lbs, and feeds on sea urchins and jellyfish. Unlike every other species, the flatback isn’t highly migratory, spending its whole life cycle close to its nesting beaches rather than crossing ocean basins. It remains too little studied for the IUCN to fully assess its conservation status.

A Shared Set of Threats, A Shared Path Forward

Every one of these species faces the same core pressures: fisheries bycatch, egg and meat harvest, coastal development and artificial lighting on nesting beaches, and marine pollution, especially plastic debris mistaken for prey. All sea turtle species found in the Americas are currently listed as Endangered or Critically Endangered by the IUCN. International agreements like CITES and the Inter-American Convention for the Protection and Conservation of Sea Turtles, alongside on-the-ground work like TLT’s, are what stand between these species and extinction.

Condensed and adapted by The Leatherback Trust from: Inter-American Convention for the Protection and Conservation of Sea Turtles (IAC) Secretariat, An Introduction to the Sea Turtles of the World, San José, Costa Rica, October 2004. Full text and references available at iacseaturtle.org.