Similar in appearance to a little snake or salamander with tiny legs, the three-toed skink (Saiphos equalis) is an interesting little Australian lizard which either lays eggs or gives live birth depending upon where it lives.
Many lizards found in colder climates use live birth with the babies developing inside the mother in thin membranes rather than thick egg shells. When they are born, the mother deposits the membrane with the baby inside and it immediately tears free. This allows the mother’s thermoregulatory behavior to keep the developing embryos at a warmer-than-ground temperature.
Lizards in warmer climates tend to lay eggs.
Individual three-toed skinks lay eggs if they live further north where it is warmer in the southern hemisphere, or give live birth if they are further south where it is cooler.
Past studies have shown that live-bearing individuals who were moved north continued to give birth and egg-laying females that were moved south continued to lay eggs. So it was thought that perhaps a female was either an egg layer or a live-bearer from a long process of evolving within the climactic conditions of its location.
Now an individual has been observed laying eggs and giving birth in a single clutch. This is the first vertebrate known to do this.
For pictures (click on the first picture to see more) and an interesting article on the topic, see the link below: