This is where that skink comes into play, the conditions changed rapidly within the species environment so the trade-offs were balanced. In colder climates, it would have been safer to keep the egg inside ready for live birth, with access to the warmth but the trade-off of using more nutrients and energy from the mother.
Those in warmer climates get deposited as regular external eggs, so they're in a bit more danger but not likely to freeze, and saves the mum's resources for herself.
So it will likely depend within each species and environment they live in =)