Our earliest vertebrate (animals with backbones) ancestors laid eggs, but over millions of years of evolution, some species began to give birth to live young.
There is a traditional dichotomy in vertebrate reproduction: species either lay eggs or have live births. However, as is often the case in biology, things aren’t as simple as they first appear, and there are a handful of vertebrate animals that do both.
One of these is the three-toed skink (Saiphos equalis). Our recent research suggests the egg-laying S. equalis may currently be in the process of transitioning from egg-laying to giving live birth.
Studying them gives us a unique opportunity to watch evolution in action. MORE
Header image: Saiphos equalis has a distinctive yellow belly, and a long, slender body, ideal for its underground lifestyle. Credit: Charles Foster.