Skink: Eggs, Babies or Both?

Sep 15, 2010 By Arati
Arati Rao's picture

A yellow-bellied three-toed skink (a type of lizard with very short legs that moves like a snake) has become the center of attraction for scientists lately. Here’s why: the skinks living in the warm coastal lowlands of Australia are oviparous (they lay eggs). But members of the same species have begun opting for live births (no eggs, directly giving birth to babies) further up in the cooler climates of the mountains. So does the yellow-bellied three-toed skink lay eggs or give birth to live babies? Both … for now!

And THAT is what is exciting. 

What's special about this?

Over time, several species of reptiles have made the transition from egg-laying to live births. But looking at a reptile giving birth to babies does not give an insight in to how they made that transition. This skink species is like a developing story! If you were a herpetologist (someone who studies reptiles), this would be a chance of a lifetime.

How does the skink do that?

Scientists know that the process of giving birth in mammals is highly advanced. Food and oxygen for the developing baby comes through a sac called the placenta. Correspondingly, when a reptile lays eggs on the ground, the nourishment for the unborn baby comes from the yolk and much needed calcium comes from the porous eggshell.

If a reptile is moving from laying eggs to live births, what might be happening to make sure that the baby gets its nourishment? The scientists decided to check what was happening in the yellow-bellied three-toed skink that lived in the cool mountains.

Well, it turned out to be a rather smooth transition! The mother’s womb seemed to secrete calcium that got absorbed into the embryo. Scientists believe that this is the beginning of placenta-formation in reptiles. The ease of the switch is likely why there have been so many instances in history of species making the change from egg-laying to live births. 

This research was published in the Journal of Morphology in August 2010 by James Stewart from East Tennessee State University and co-authors.

Which reptile fascinates you the most and why?