Turtles were already carrying their homes around 220 million years ago. They outlasted the dinosaurs. Now about half of all species are at risk.
The same basic body plan spans a tortoise you could hold in one hand and a sea turtle that dives past 1,000 metres and weighs as much as a grand piano.
Most turtles have no sex chromosomes. The temperature of the nest during the middle third of incubation sets whether each egg hatches male or female.
Below about 27.5 °C, sea turtle clutches hatch mostly male.
Near 29 °C, a clutch comes out roughly half and half.
Above about 30.5 °C, hatchlings are mostly female. Some beaches now produce almost no males.
Hatchlings find the sea by heading toward the brightest horizon. Shield or switch off beachfront lights during nesting season.
Collection for the pet trade empties whole populations. If you keep a turtle, make sure it was captive-bred, and never release it.
Freshwater turtles cross roads to nest. If it is safe, move one across in the direction it was already heading.