BIODIVERSITY

This skink has a surfeit of toes.

We all know that lizards are coldblooded and lay eggs. Some of us (such as the readers of this magazine) know that the some of the Scincidae - the skinks, including our backyard favourite the blue-tongue - give birth to live young.

(To be clear: they still start off in eggs, the mother just doesn’t lay the eggs but rather incubates them inside her and then the babies hatch and crawl out - it’s much more primitive than the mammalian womb.)

But because nature likes to try everything, here’s an example of a single species of skink where some populations lay eggs, and some give birth to live young.

Saiphos equalis, like quite a few Aussie lizards including the pinktongued skink, is the only member of its genus. It’s a slinky, snaky, literally yellow-bellied lizard that grows to about 20 cm. They’re most often seen when you turn over a rotting log, and you’d easily mistake it at first for either a common garden skink, a really fat nightcrawler of an earthworm, or (if you’re the nervous type) a small snake.

If you’re confident enough to nab one, you can see it has three stubby little toes on its tiny front feet. And when you let it go, it will dive straight down into loose dirt or leaf-litter and disappear.

Saiphos is especially unusual because not only does it lay eggs (on the coast) or give birth to live young (in the mountains), it has a very short incubation period for its eggs - just five days. Well, actually it has TWO different incubation periods: some populations also incubate for 15 days.

Both are much shorter than the typical skink incubation period of 30 days.

Again it’s all about climate: the Saiphos who live at over 1000m in the mountains give birth to live young in a transparent sack. The ones who live on the sides of the mountains or uplands lay eggs that only have partially-formed shells and the babies inside are already quite developed. These hatch within a week. Only the coastal populations incubate for 15 days.

Herpetologists think this might be evidence that the three-toed skink is in evolutionary transition from egg-laying to true “viviparity”. Many thousands from years from now, they’d join the bluetongues as a fully live-bearing lizard.