Fossil 'is first pregnant lizard'

Half of the pregnant Yabeinosaurus (Image: Yuan Wang/IVPP) The lizard was just days from giving birth when it died and was buried

Related Stories

A 120-million-year-old fossil is the oldest pregnant lizard ever discovered, according to scientists.

The fossil, found in China, is a very complete 30cm (12in) lizard with more than a dozen embryos in its body.

Researchers from University College London, who studied the fossil, say it was just days from giving birth when it died and was buried during the Cretaceous period.

The team reports the findings in the journal Naturwissenschaften.

Start Quote

When I examined it under the microscope, I could see all these little babies”

End Quote Prof Susan Evans University College London

The fossil is especially interesting to scientists because it is a reptile that produced live young rather than laying eggs.

Only 20% of living lizards and snakes produce live young, and this shows it is an ancient, if unusual, trait.

"I didn't think much of the fossil when I first saw it," said Prof Susan Evans, joint lead author of the paper, from University College London.

But when her colleague, Yuan Wang, from the Chinese Academy of Sciences, examined the fossil he spotted the tiny remains of at least 15 almost fully developed embryos inside it.

"Sure enough, when I examined it under the microscope, I could see all these little babies," Prof Evans recalled.

Close-up of one of the embryos inside Yabeinosaurus The heads of at least 15 lizard embryos are visible inside the body of the fossil

The fossil is so well preserved that the minuscule teeth of the developing young are visible on very close inspection.

"This specimen is the oldest pregnant lizard we have seen," said Prof Evans.

"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 the fossil records only contained examples of marine lizards giving birth to live young.

Scientists thought that, in extinct reptiles, live birth was restricted to aquatic species, such as marine ichthyosaurs. These creatures would have been able to move through water with relative ease, even when heavily pregnant.

An iguana embryo of approximately the same age as those within the body of the Yabeinosaurus fossil Most lizard species, such as iguanas, lay eggs

Prof 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 fossil comes from world famous rocks of the Jehol Group in north-eastern China, where the fine limestone there has been worn away to gradually reveal hundreds of exquisite specimens of dinosaurs, but also fish, amphibians, reptiles, birds and mammals, plants and invertebrates.

The mother lizard has been identified as a specimen of Yabeinosaurus, a large, slow-growing and relatively primitive lizard.

More on This Story

Related Stories

The BBC is not responsible for the content of external Internet sites

More from nature

  • Cardinal fish and ostracodFish filmed spitting 'fireworks'

    Film crew captures ostracods' spectacular defensive lightshow that makes predatory fish spit them out.

  • Arapaima'Locally extinct'

    A giant fish which used to dominate the Amazon river is now absent in many areas


  • DragonflyRapid reactions

    Dragonfly's super quick reactions recorded in slow motion by BBC film-makers


  • Wingless adult male of the midge Belgica antarcticaExtreme survivor

    Antarctic midge's small genome may be an adaptation to its extreme environment


  • Myotis midastactus specimen (previously identified as Myotis simus)Golden discovery

    A bat from Bolivia is described as a new species by scientists


  • Dinosaurs 'shrank' to become birds

    Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, new research shows.

  • Would we starve without bees?

    Honey bees are under threat, and as pollination significantly contributes to the food we eat, what would we do without them?

  • Eggshells may act like 'sunblock'

    Birds' eggs show adaptations in pigment concentration and thickness to allow the right amount of sun for embryos, scientists say.

  • Female shrimps are more aggressive

    Female snapping shrimps are more aggressive than males when defending their territories despite their smaller claw size, a study shows.

BBC iWonder

  • Honey bee close-upInsect intelligence

    Are honey bees as smart as your sat nav?

  • Tyrannosaurus rex skull (c) Mark Williamson / Science Photo LibraryDinosaur dynasty

    One group of dinosaurs survived and their descendants can be seen all around us today


  • Brown rat cluse upRise of the rodent

    Reports of giant, 'super rats' are filling the headlines. But why are we being overrun by rats?


  • Cuckoo portraitHoliday hotspot

    What makes the UK such an attractive destination for visiting wildlife?


Awesome! And there's nothing common about such beauty.

Elaine Bernon on Facebook comments on the trio of common blue butterflies in our Photo of the Day.

Things To Do

RUN BY THE BBC AND PARTNERS

More Nature Activities >

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.