Changes

The transition from oviparous animals to viviparous animals is a well observed and documented process. A notable example is that of the Skink group of lizards, which have been observed in several stages of egg cell retention in the transition from oviparous birth to viviparous birth, particularly when environmental conditions have forced such a change where it is beneficial to retain the egg <ref>http://www.jstor.org/pss/2460311</ref>.

The transition from oviparous animals to viviparous animals is a well observed and documented process. A notable example is that of the Skink group of lizards, which have been observed in several stages of egg cell retention in the transition from oviparous birth to viviparous birth. This has been observed particularly when environmental conditions have forced such a change where it is beneficial to retain the egg <ref>Live-bearing in lizards and snakes. R, Shine and J, Bull., The American Naturalist. Vol 113, no 6, 1979.</ref>.