In Australia is a unique animal, a lizard known as a three-toed skink. It is one of the very few vertebrate animals that both lays eggs and gives birth to live young, and in a recent strange discovery a pregnant skink was for the first time observed to use both methods in the same litter.
In a world first, researchers at the University of Sydney have observed a normally live-bearing Australian lizard lay three eggs and then weeks later, give birth to a live baby from the same pregnancy. This is the first time such an event has been documented in a single litter of vertebrate babies.
The three-toed skink (Saiphos equalis) is one of only a handful of rare “bimodally reproductive” species, in which some individuals lay eggs and others give birth to live babies. But up until now, no vertebrate has ever been observed to do both in one litter.
“It is a very unusual discovery,” said Dr Camilla Whittington, from the School of Life and Environmental Sciences and Sydney School of Veterinary Science at the University of Sydney.
The three-toed skink is native to the east coast of Australia. In the northern highlands of New South Wales the animals normally give birth to live young, but those living in and around Sydney lay eggs.
“We were studying the genetics of these skinks when we noticed one of the live-bearing females lay three eggs,” Dr Whittington said. “Several weeks later she gave birth to another baby. Seeing that baby was a very exciting moment!” …
There are at least 150 evolutionary transitions from egg-laying to live-bearing in vertebrates said Dr Whittington …
“The earliest vertebrates were egg-layers, but over thousands of years, developing embryos in some species were held inside the body for longer, until some animals began to give live birth. People mostly think about humans and other mammals giving birth. But there are many species of reptile that give birth, too.”
Dr Whittington said that the unusual observation of both egg laying and live birth in a single litter shows that the three-toed skink is an ideal model for understanding pregnancy. …
Here’s a video of some three-toed skinks.
They seem to be evolutionarily transitional animals in terms of legs as well. They look like snakes with tiny legs.