Live birth in lizards developed earlier than thought

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File:Yabeinosaurus tenuis Beijing Museum of Natural History 2010 Sep 04.JPG
Yabeinosaurus tenuis Beijing Museum of Natural History/Jason Quinn

In “Fossil ‘is first pregnant lizard,'” (BBC News , July 21, 2011), Victoria Gill tells us of a lucky find in China: A 120-million-year-old fossil pregnant lizard, 30 cm long, very complete, and within days of giving birth to about a dozen sharply detailed embryos. And,

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.

[ … ]

“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.”

Apparently, mm was a Yabeinosaurus, thoght to be a “primitive” lizard.

File under: Change name of that “Overwhelming evidence for evolution” file cabinet to “Earlier than thought”

See also: Stone tools nearly two million years old, and Michael Cremo is still wrong?

No fossil rabbbits in the preCambrian, but what about complex cells?

Ancient and well-travelled worm

Earlier than thought: Freshwater animals

5 Replies to “Live birth in lizards developed earlier than thought

  1. 1
    DrREC says:

    There have been direct observations of the transition from egg-laying to retaining eggs that hatch internally.

    “In general, the results suggest the move from egg-laying to live birth in reptiles is fairly common—at least in historic terms—because it’s relatively easy to make the switch, Stewart said.

    “We tend to think of this as a very complex transition,” he said, “but it’s looking like it might be much simpler in some cases than we thought.”


  2. 2
    ScottAndrews says:

    How do you define “direct observation?”

  3. 3
    SCheesman says:

    What I find interesting in the National Geographic article referenced by DrREC above is the following:

    Evolutionary records shows that nearly a hundred reptile lineages have independently made the transition from egg-laying to live birth in the past, and today about 20 percent of all living snakes and lizards give birth to live young only.

    The “standard” conclusion, of course, is that so many do the transition because it is a “simple” Darwinian process for this particular circumstance.

    I would propose that the ID take on this would be that the transition is “built in” to those lizards’ genomes, and the transition is either triggered epigenetically, or by some unknown trigger process that invokes the built-in programme.

  4. 4
    SCheesman says:

    A couple of questions:

    a) Might it be possible to reverse the process (e.g. go from live birth to egss)?

    b) Has that been observed? If not, then why does the transition just go one way?

  5. 5
    Elizabeth Liddle says:

    I’m not sure it does just go one way.

    Some sharks have live young, some lay eggs.

    Of course humans also have eggs 🙂

    Egginess isn’t that discrete.

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