(CNN)For most of the animal kingdom, babies are born in one of two ways: their parent either lays eggs or gives birth to live offspring.
An extraordinary feat pulled off by a lizard could suggest the species is going through a rare evolutionary transition
Recently, a three-toed skink (Saiphos equalis) pulled off an extraordinary feat: It laid three eggs and delivered another baby through live birth in the same pregnancy. That suggests that the lizard species is in a rare transitional form between egg-laying and live-bearing animals, according to a study published in Molecular Ecology last month.
"We affectionately call the three-toed skink 'the weirdest lizard in the world' -- but it can tell us a lot about the evolution of reproductive strategies," Camilla Whittington, one of the study's lead authors and an evolutionary biologist at the University of Sydney, wrote in an email to CNN.
Three-toed skinks, found in Australia, are already a fascinating species for evolutionary scientists, explains Whittington. One reason is that some populations reproduce by laying eggs, while others reproduce through live birth.
The mode skinks use to reproduce generally corresponds with their environment. Skinks around the Sydney area lay eggs, albeit ones with thin shells and embryos that are almost completely developed. In northern parts of Australia, the skinks give birth to live young.
But never before had scientists seen a species lay eggs and experience live birth in a single pregnancy until it was observed in the three-toed skink last year, Whittington wrote. It was the first record of a vertebrate doing so.
There are a couple of explanations as to why the skink both laid eggs and had a live baby in the same pregnancy, Whittingon said.
One is that it was a form of "bet-hedging," meaning that the ability to switch between laying eggs and live birth could provide the lizard an advantage in unpredictable environments.
"For example, if it's cold or dry, it might be risky to lay eggs in an unprotected nest, and better for the mums to carry the babies until development is complete," she wrote. "If there are a lot of predators around and pregnant mums find it harder to escape, it might be risky to carry babies to term. Mothers that are able to act flexibly could therefore have an advantage in an unpredictable environment."
Another explanation is that some feature of the environment could have caused the skink in question to lay part of her clutch abnormally early. Still, Whittington said, two of the skink's eggs hatched to healthy baby lizards, which means that if this phenomenon happened in the wild, the babies could still be viable.
The finding could mean that the skink is transitioning to only laying eggs or only experiencing live birth. But scientists say it's too soon to tell which direction it's moving in.
In general, animals that give birth to live young have evolved from ancestors that laid eggs and it would be rare for an animal to evolve in the other direction, according to Whittington. And it's worth pointing out that when th