viviparous

Viviparous describes organisms that give birth to live young that have developed inside the parent's body. The term derives from Latin vivi, meaning alive, and parere, to bring forth. In zoology, viviparity refers to live birth, contrasting with oviparity (egg-laying) and ovoviviparity, in which embryos develop inside eggs retained within the mother and are nourished mostly by yolk.

In true viviparity, developing embryos receive nutrients from the mother through a specialized connection such as a placenta or placental-like tissues. The form and degree of maternal provisioning vary among groups. Mammals typically possess a placenta that enables nutrient and waste exchange between mother and fetus. In some fish, reptiles, and amphibians, nourishment may occur via a yolk sac, uterine secretions, or other maternal tissues, with or without a direct blood connection.

Examples include humans and most other mammals; many sharks and some rays are viviparous, often with yolk-sac or placental nourishment. Among reptiles, several species of lizards and snakes are viviparous; the common lizard Zootoca vivipara is a well-documented example. Viviparity can confer advantages in environments where eggs are at risk from predation or harsh conditions, but it also imposes higher energetic costs on the mother and can limit litter size and timing.

In botany, vivipary refers to seeds germinating while still attached to or within the parent plant, a distinct phenomenon from animal viviparity.