Viviparous

Reproductive mode

There is no relationship between sex-determining mechanisms and whether a species bears live young or lays eggs. Temperature-dependent sex determination, which cannot function in an aquatic environment, is seen only in terrestrial viviparous reptiles. Therefore, marine viviparous species, including sea snakes and, it now appears, the mosasaurs, ichthyosaurs, and plesiosaurs of the Cretaceous, use genotypic sex determination (sex chromosomes), much as birds and mammals do. Genotypic sex determination is also found in most reptiles, including many viviparous ones (such as Pseudemoia entrecasteauxii), whilst temperature dependent sex determination is found in some viviparous species, such as the montane water skink (Eulamprus tympanum).