Researches from University College London have studied a 120 million year old fossil, which has been discovered to be the oldest pregnant lizard ever found. The team said the lizard from the Cretaceous period was only a few days away from giving birth when it died.
The report, found in the journal Naturwissenschaften, details the interest of the reptile that gave birth to live young rather than through laying an egg. Of modern lizards and snakes, only 20% give birth to live young and the existence of this fossil shows that the characteristic is prehistoric.
Professor Susan Evans from University College London co-wrote the paper with Yuan Wang from the Chinese Academy of Sciences. She said, “I didn’t think much of the fossil when I first saw it.”
However, after Wang took a look at the fossil under the microscope, he saw nearly 15 late stage embryo remains inside. Professor Evans then spotted them, adding, “Sure enough, when I examined it under the microscope, I could see all these little babies.”
Upon taking a closer look, even the microscopic teeth of the embryos can be seen. Professor Evans confirmed that these were the oldest lizard embryos ever found, saying, “This specimen is the oldest pregnant lizard we have seen.
“It implies physiological adaptations, like adequate blood supply to the embryos and very thin shells – or no shells at all – to allow oxygen supply, evolved very early on.”
Up until now, only marine lizards, such as ichthyosaurs, were thought to have experienced live births, with the only examples being aquatic animals. A logical reason for this would be that the lizards in water would be able to support even heavily pregnant bodies over lizards on land.
Professor Evans said, “We do know that this lizard lived near to water and we think it likely that they could swim even though they primarily lived on land.
“This would make sense as a pregnant lizard would be less constrained by carrying offspring – she’d be able to escape into water if a hungry dinosaur came along.”
The specimen was found in the world famous rocks of the Jehol Group in northeastern China and has been identified as a Yabeinosaurus, which was primitive, large, and grew slowly.