and most lizards, the sex of the developing embryo is determined by the temperature of the surroundings, with the species determining which gender is favored at cool versus warm temperatures. Not all reptiles lay eggs; some are viviparous ("live birth"). This adaptation may have allowed reptiles to inhabit new habitats, especially in colder climates.

Dinosaurs laid eggs, some of which have been preserved as petrified fossils. Soft-shelled dinosaur eggs are less likely to be preserved, so most of the