Lacerta vivipara Lichtenstein, 1823
The viviparous lizard or common lizard, Zootoca vivipara (formerly Lacerta vivipara), is a Eurasian lizard. It lives farther north than any other reptile species, and most populations are viviparous (giving birth to live young), rather than laying eggs as most other lizards do. It is the only species in the monotypic genus Zootoca.
Zootoca vivipara can be seen in a few different colors. Female Zootoca vivipara undergo color polymorphism (biology) more commonly than males. Female lizards display a variety of ventral coloration, ranging from pale yellow to bright orange and a mixed coloration. There have been many hypothesis for the genetic cause of this polymorphic coloration. These hypothesis test for coloration due to thermoregulation, predator avoidance, and social cues, specifically sexual reproduction. Through an experiment conducted by Vercken et. al., color polymorphism in viviparous lizard was caused by social cues, rather than the other hypotheses. More specifically, the ventral coloration that is seen in female lizards is associated with patterns of sexual reproduction and sex allocation. 
The length of the body is less than 12 cm (5 in) (excluding the tail). The tail is up to twice as long as the body, although it is often partially or wholly lost. The limbs are short, and the head is rather round. Males have more slender bodies than females. The neck and the tail are thick. The collar and other scales seem jagged.
The colour and patterning of this species is variable. The main colour is typically medium brown, but it can be also grey, olive brown or black. Females may have dark stripes on their flanks and down the middle of their backs. Sometimes females also have light-coloured stripes, or dark and light spots along the sides of their backs. Most males and some females have dark spots in their undersides. Males have brightly coloured undersides – typically yellow or orange, but more rarely red. Females have paler, whitish underparts. The throat is white, sometimes blue.
The viviparous lizard is widely distributed throughout Europe and Asia. Its range extends to the north of the Arctic Circle. It ranges from Ireland to Hokkaidō and Sakhalin. It is absent from most of the Mediterranean area, although it occurs in northern Spain, northern Italy, Serbia, Republic of Macedonia and Bulgaria. It is also absent from the area surrounding the Black Sea.
In the southern parts of its distribution range, the species lives at high elevations, occurring as high as 3,000 metres (9,800 ft) above sea level in the Alps. In these areas, the viviparous lizard lives in damp places or near water, including meadows, swamps, rice fields, by brooks and in damp forests. In the northern part of the range, the species is also found in lowlands, where it occurs in drier environments, including open woodland, meadows, moorland, heathland, fens, dunes, rocks, roadsides, hedgerows and gardens. It lives mainly on the ground, although it may climb onto rocks, logs and low-growing vegetation.
The viviparous lizard feeds on invertebrates, mostly small insects. It shakes larger prey in its jaws before chewing it and swallowing it whole. In early spring, late autumn, and cool summer days, it basks in the sun to reach its optimum body temperature, which is about 30°C (86°F).
These lizards mate in April or May. Males take females in their jaws before mating – if the female is not interested, she will bite the male fiercely. The offspring develop for about three months inside the female.
The name of the species is derived from its ability to give birth to live young, an adaptation to a cool climate, but some southern populations are oviparous (egg-laying). The three to 10 young (or eggs) are usually produced in July. The blackish young measure about 3 cm (1.2 in), and when first born are surrounded by egg membrane, from which they break free after about a day. Males reach sexual maturity at two years old, females at three years old. Individuals from viviparous and oviparous populations may be hybridised, but with significant embryonic malformation. Viviparous Z. vivipara do develop placentae to facilitate pregnancy but there is no substantial transport of nutrients as seen in some other species of viviparous reptiles (e.g. Pseudemoia entrecasteauxii).
In northern regions, viviparous lizards begin hibernation in September or October, underground or in log piles. Hibernation ends about mid-February. Further south, the species is active throughout the year.
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- A. Agasyan; et al. (2010). "Zootoca vivipara". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved May 11, 2012.
- Josef Friedrich Schmidtler1 & Wolfgang Böhme (2011). "Synonymy and nomenclatural history of the Common or Viviparous Lizard, by this time: Zootoca vivipara (Lichtenstein, 1823)" (PDF). Bonn Zoological Bulletin 60 (2): 214–228.
- Harris, D. J. and M. A. Carretero. (2003). Comments on the taxonomic value of (sub)genera within the family Lacertidae (Reptilia). Amphibia-Reptilia 24 119-22.
- Vercken, E., Massot, M., Sinervo, B., Clobert, J.2006. Colour Variation and Alternative Reproductive Strategies in Females of the Common Lizard Lacerta vivipara. Journal of Evolutionary Biology 20(1): 221-232
- Heulin, B., Arrayago, M. J., and Bea, A. 1989. Expérience d'hybridation entre les souches ovipare et vivipare du lézard Lacerta vivipara. Comp. Rend. Acad. Sci. Series 3 308: 341-346 (cited by the Reptile Database).