Seven sea turtle species still patrol the world's oceans
Marine turtles in the chelonioid superfamily still number seven living species worldwide, spanning hard-shelled cheloniids and a single leathery giant. Adults of each kind match in body size by sex, yet males trail longer tails that end near a distal cloaca.
The hard-shelled majority—greens, loggerheads, hawksbills, flatbacks, and both ridleys—contrast with the leatherback's flexible dermochelyid covering. All belong to order Testudines and the cryptodiran neck-tucking group, even while flippers and salt glands suit open-ocean life far from pond turtles.
Life at sea reshaped the body. A fusiform outline, tapered at both ends, cuts drag and lets them swim fast, but it leaves no room to pull head and limbs inside the shell the way many turtles can. Their limbs, which first evolved for getting around, now also hold, swipe and forage food. The leatherback dwarfs the rest at 1.4 to over 1.8 metres and 300 to 640 kilograms; green turtles, the runners-up, reach about 120 centimetres, and Kemp's ridley, the smallest, about 60.
Five of the seven species are listed as threatened on the IUCN Red List. Some ranges are tiny: flatbacks live only off northern Australia, and Kemp's ridleys only in the Gulf of Mexico and along the US East Coast. Youngsters spend their first three to five years drifting in open-ocean seaweed mats, green turtles often in Sargassum, before moving nearer shore as adults, when females come back to sandy beaches to lay eggs. When COVID-19 cut human activity in 2020, nesting rose in parts of Thailand and Florida, possibly helped by less plastic and light pollution.
The lineage is old. Marine turtle fossils such as Europe's Plesiochelys date to the Late Jurassic, 150 million years ago, and the name Chelonioidea comes from the Ancient Greek word for tortoise.
Source: Sea turtle
