![]() ![]() With this transition, some structures were lost, including the hard outer eggshell. Many physiological changes were necessary for live birth to have evolved from egg-laying. There is strong evidence that egg-laying is ancestral to live birth, meaning it came first. The embryos can rely entirely on yolk for nutrition, or the parents can provide supplementary nutrition, sometimes via a placenta (as in humans). In contrast, “viviparous” animals carry embryos internally until they are fully developed. In other oviparous species, including birds and some lizards and snakes, eggs are fertilised inside the mother, an eggshell is added, and then eggs are laid.ĭepending on the species, much or all of the nutrition needed to grow a healthy baby is supplied in the egg yolk. For instance, many fish species spawn eggs that are fertilised externally. There are two main reproductive strategies in vertebrates.Īnimals that lay eggs are called “oviparous”.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |