AsianScientist (Jul. 26, 2011) – Two scientists from the University College London and the Chinese Academy of Sciences have discovered a 120 million-year-old fossil. But that is not all, the fossil also happens to be pregnant.
The fossil was discovered by Susan Evans, a professor from University College London, in the Jehol region of Northeast China, a treasure trove of hundreds of dinosaur, amphibian, reptile, fish, bird, mammal, invertebrate, and plant fossil specimens.
Initially, Evans did not pay much attention to the fossil, which has since been identified as Yabeinosaurus, a primitive lizard similar to the modern gecko.
But Yuan Wang from the Chinese Academy of Sciences examined the fossil and discovered 15 tiny fossilized skeletons of baby lizard embryos within it.
This discovery was published in the July 2011 edition of the journal Naturwissenschaft.
“We previously thought that lizards adapted to live birth after mammals, but now it looks like it happened at roughly the same kind of time,” Evans said.
“This specimen is the oldest we have seen, which 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,” she added.
The embryos were almost fully developed, and researchers believe that the foot-long mother lizard died just days before giving birth and was buried in mud which turned to rock. She may have lived close to water in order to flee from predators.
The fossil discovery also reveals that land lizards were giving birth to live young in the Early Cretaceous period – earlier than previously thought. Up until now the fossil records only contained examples of marine lizards giving birth to live young.
For lizards, egg-laying is usually associated with cold, dangerous environments where eggs are unlikely to survive. With a switch to live births, the extra weight carried throughout gestation may also limit the mother’s movement and ability for self-defense.
The article can be found at: Wang Y et al. (2011) A gravid lizard from the Cretaceous of China and the early history of squamate viviparity.
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Source: Physorg.com.
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