The diversity of lizards, a group within the reptiles, is extensive, and their methods of reproduction reflect this wide variation. Unlike mammals, which are uniformly live-bearing, lizard reproductive strategies span a spectrum from familiar egg-laying to true live birth. The process by which a baby lizard enters the world is dictated by its species’ evolutionary history and its environment.
The Most Common Way: Egg Laying (Oviparity)
The dominant reproductive mode among lizards globally is oviparity, or egg-laying, characteristic of the majority of species. A female deposits her clutch of eggs in a protected location, such as a burrow, under a log, or within a communal nesting site. Lizard eggs are typically leathery and porous, allowing them to absorb moisture from the surrounding substrate as the embryo develops.
The eggs of most geckos are an exception, featuring shells that rapidly harden, preventing subsequent change in size or shape. Embryos rely entirely on the yolk for nutrition until they are ready to hatch. The incubation period depends on the external environment, with temperature and humidity being the most significant factors. In many species, the incubation temperature determines the sex of the hatchlings, known as Temperature-Dependent Sex Determination (TSD). When fully developed, the baby lizard uses a temporary structure called an egg tooth to cut its way out of the shell, a process called eclosion.
The Alternative: Internal Development and Live Birth (Viviparity)
A significant minority, about 20% of lizard species, have evolved to give birth to live young, a reproductive strategy common in colder or high-altitude environments. Retaining the eggs internally allows the mother to regulate the temperature of the developing embryos by basking or seeking shade, a major advantage in cooler climates. This internal gestation exists along a continuum, with two main forms often discussed.
Ovoviviparity
In ovoviviparity, the eggs are retained inside the mother’s body, and the embryos primarily rely on the large yolk sac for nutrition, similar to an externally laid egg. The mother provides protection and gas exchange, but minimal additional nutrients. The young hatch immediately inside or just after the mother expels the egg membrane.
True Viviparity
In true viviparity, the mother develops a specialized placenta-like structure to provide sustained nutrition to the developing young. This structure is formed from the mother’s uterine tissue and the embryo’s membranes, facilitating the transport of nutrients and gases. This placentotrophy, or placental nutrition, allows the young to emerge fully formed and relatively large. Viviparous species give birth to miniature versions of the adult, which are immediately mobile and independent. The neonate emerges from the female, often still enclosed in a thin membrane that it must quickly break out of.
Independent Life Begins: Post-Hatching and Parental Care
Regardless of whether they emerge from an egg or are born live, most baby lizards are considered precocial. This means they are relatively mature and mobile from the moment of birth or hatching, possessing the necessary abilities to hunt, hide, and survive on their own. This independence contrasts sharply with the altricial young of many mammals and birds that are born blind and helpless.
The vast majority of lizard species exhibit no parental care after the young have hatched or been born. The female usually leaves the nesting site or birth location shortly after the event, leaving the offspring to navigate survival challenges alone. A few species, such as certain skinks and some anguids, may guard their eggs or remain near the hatchlings for a short period for protection, but this is an exception. The first few weeks of life are a period of high vulnerability, as the small size of the baby lizard makes it susceptible to predators.