Fine.
Viviparous evolution in squamates, which skinks are, has been observed many times (100 ), and the evolution has been strongly linked to the cold climate model. That is those lizards which remain oviparous in cold climates (as well as several other selective pressures) produce fewer and weaker offspring, while viviparous lizards, those that are better at egg retention, produce more offspring and become more dominant. Over time the egg shell thickness is reduced and eventually evolves into complex placenta, which has been observed several times.
"Squamate reptiles provide an excellent model system for studies on the evolution of viviparity because live-bearing reproduction has evolved in the Squamata at least 100 times (Blackburn, 1999), and complex placentae have evolved four or five times (Thompson and Speake, 2006)."
(Source) (sorry to use this twice, it just demonstrates my point)
It has been shown through observed placentation of lizards.
The following is an explanation of the evidence and cases for the stages of the evolution of the placenta in squamates, that the skink will likely follow if the evolution becomes successful. (Sorry about the wall of quoted text, it's just that I originally wrote out an explanation myself, but my browser crashed and lost it *grrr*. and this explains it better than I can anyway) (source)
"Multiple forms of squamate viviparity and placentation have evolved, each involving modification of extra-embryonic and uterus membranes from an ancestral oviparous pattern. Most squamates reproduce by simple yolk-dependent (lecithotrophic) viviparity, featuring retention of large, yolk-rich eggs, eggshell reduction to a thin membrane, and limited exchange of nutrients for growth (histotrophy) between the uterine epithelium and isolated yolk mass omphalopleure. Accepting the definition of Mossman (1937) that a placenta is “any intimate apposition or fusion of the fetal organs to the maternal (or paternal) tissues for physiological exchange”, this arrangement has been termed an ‘omphaloplacenta’.Gas exchange occurs across the well-vascularised interface between the outer-most embryo-derived membranes (the chorion and allantois) and the directly apposed uterine epithelium: this simple juxtaposition of fetal and maternal epithelia is technically termed a Type I or ‘epitheliochorial chorioallantoic’ placenta.
Moving on to consider other forms, some members of the Scincidae (e.g. Niveoscincus spp.) have a morespecialised, Type II, placenta. Here the chorioallantoic placenta comprises a layer of large, cuboidal chorion cells closely associated with a ridged uterine epithelium of flattened (or ‘squamous’) cells, underlain by a dense capillary network. Yet more complex, Type III placentation is seen in a number of Australian skinks (e.g. Pseudomoia spp.) and the Mediterranean lizard Chalcides chalcides. This morphotype is typified by differentiation of part of the chorioallantoic placenta into extensively folded, interdigitated uterine and chorionic epithelia. This structure is specialised for matrotrophic nutrient transfer, and is termed a ‘placentome’. Surrounding the placentome, gas exchange is facilitated by a ‘paraplacentome’ comprising microvilliated, enlarged chorionic epithelial cells apposed to a highly vascularised uterine epithelium.
Finally, in the most advanced, Type IV placentation morphotype, famously found in the South American genus Mabuya, complex adaptations converge in intricate detail upon the derived placentation of eutherian mammals. Placental features shared between mabuyids and eutherians include a placentome of densely folded fetal-maternal epithelia, and a surrounding chorioallantoic placenta (paraplacentome) covered in clusters of cells (chorionic areolae) specialised to absorb products secreted from complementary uterine glands, and giant, binucleate chorion cells covered in microvilli. Adding to the list of remarkable convergences, both Mabuya and eutherians also ovulate minuscule (~1mm) yolk-free ova, provide >99% of embryonic nourishment by placentotrophy, and do so over a protracted gestation period (8-12 months)."
Anyway, now to defend my point about it being evolution in action in this particular Skink. I believe that the selective pressures that form the eventual evolution which have been observed in other squamate are already happening in this case, and it will continue to do so if they continue to live in the cold environment over the coming generations and eventually they will develop more complex placentas. Even though it is early stages, this is the first step for this particular evolution for this lizard that will follow a path that many similar lizards have taken in the past. It may not be a significant evolution yet, but it is evolution that has been set in motion.
As the article said.
"Now we can see that the uterus secretes calcium that becomes incorporated into the embryo—it's basically the early stages of the evolution of a placenta in reptiles"
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