Oviparous

Oviparous describes animals that lay eggs in which the embryo develops until hatching, with little or no sustained nutrition from the parent after fertilization. The term derives from Latin ovum, meaning egg, and parere, to bring forth. In oviparous species, fertilization is typically internal, followed by laying eggs that develop outside the body. Development may occur externally in the environment or within a nesting site, after which the young hatch.

Eggs vary widely in structure. Some have hard, calcified shells as in birds, while others possess leathery or gelatinous coverings as seen in many reptiles, fish, and invertebrates. Inside, eggs are generally yolk-rich to support embryonic growth, though some species supply additional parental care or incubation warmth after laying.

Taxonomic distribution is broad. Birds, most reptiles, and monotremes (the egg-laying mammals such as the platypus and echidnas) are classic examples. Many fishes, amphibians, and numerous invertebrates also reproduce oviparously, using a variety of egg-laying strategies.

Oviparity is contrasted with viviparity, where young are born live, and ovoviviparity, where eggs hatch inside the mother before birth. Some species exhibit different degrees of parental involvement after laying, ranging from no care to guarding and providing heat or food for eggs.

Evolutionarily, oviparity is widespread and ancient, offering advantages in dispersal and reduced maternal energy expenditure during gestation, while exposing eggs to environmental risks and predation.