Evolution Genetics News

Snakes didn’t just evolve from lizards?

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More complex than thought? From ScienceDaily:

Rather than snakes evolving from a lizard ancestor to a more simplified body form, the researchers say their findings suggest other animals gained more complex vertebral columns as they evolved.

The study provides new perspective on Hox genes, which govern the boundaries of the neck, trunk, lumbar, sacral and tail regions of limbed animals. The functions of Hox genes previously were thought to have been disrupted in snakes, resulting in seemingly simplified body forms.
Snakes differ from mammals, birds and most other reptiles because they lack forelimbs, shoulder girdles and breastbones. It was thought that when they lost their limbs, they also lost the regional distinctions that separated their backbones into neck, trunk, lumbar and other regions.

Yet when Head and Polly examined the shapes of individual vertebral bones in snakes, lizards, alligators and mice, they found snakes had regional differentiation like that of lizards.

“If the evolution of the snake body was driven by simplification or loss of Hox genes, we would expect to see fewer regional differences in the shapes of vertebrae,” Head said. “Instead, what we found was the exact opposite. Snakes have the same number of regions and in the same places in the vertebral column as limbed lizards.”

Of note:

“Our findings turn the sequence of evolutionary events on its head,” Polly said. “It isn’t that snakes have lost regions and Hox expression; it is that mammals and birds have independently gained distinct regions by augmenting the ordinary Hox expression shared by early amniotes.”

Amniotes are the group of vertebrates that lay shelled eggs. They include reptiles, mammals and their predecessors.

Convergent evolution?

Not only did Head and Polly find that snakes were as differentiated as lizards, but when they compared regions in snakes with Hox gene expression, they found the two matched.

Here’s the abstract:

Hox genes regulate regionalization of the axial skeleton in vertebrates1, 2, 3, 4, 5, 6, 7, and changes in their expression have been proposed to be a fundamental mechanism driving the evolution of new body forms8, 9, 10, 11, 12, 13, 14. The origin of the snake-like body form, with its deregionalized pre-cloacal axial skeleton, has been explained as either homogenization of Hox gene expression domains9, or retention of standard vertebrate Hox domains with alteration of downstream expression that suppresses development of distinct regions10, 11, 12, 13. Both models assume a highly regionalized ancestor, but the extent of deregionalization of the primaxial domain (vertebrae, dorsal ribs) of the skeleton in snake-like body forms has never been analysed. Here we combine geometric morphometrics and maximum-likelihood analysis to show that the pre-cloacal primaxial domain of elongate, limb-reduced lizards and snakes is not deregionalized compared with limbed taxa, and that the phylogenetic structure of primaxial morphology in reptiles does not support a loss of regionalization in the evolution of snakes. We demonstrate that morphometric regional boundaries correspond to mapped gene expression domains in snakes, suggesting that their primaxial domain is patterned by a normally functional Hox code. Comparison of primaxial osteology in fossil and modern amniotes with Hox gene distributions within Amniota indicates that a functional, sequentially expressed Hox code patterned a subtle morphological gradient along the anterior–posterior axis in stem members of amniote clades and extant lizards, including snakes. The highly regionalized skeletons of extant archosaurs and mammals result from independent evolution in the Hox code and do not represent ancestral conditions for clades with snake-like body forms. The developmental origin of snakes is best explained by decoupling of the primaxial and abaxial domains and by increases in somite number15, not by changes in the function of primaxial Hox genes9, 10. (paywall)

19 Replies to “Snakes didn’t just evolve from lizards?

  1. 1
    awstar says:

    Rather than snakes evolving from a lizard ancestor to a more simplified body form, the researchers say their findings suggest other animals gained more complex vertebral columns as they evolved.

    Evolution theory says some animals gain complexity and some animals lose complexity.

    Where is the information value in that? It’s like saying “it’s raining outside and not raining outside”

  2. 2
    Zachriel says:

    Snakes are tetrapods.

  3. 3
    Joe says:

    Snakes are tetrapods without the tetrapods!

  4. 4
    ppolish says:

    Snakes did not evolve from Schnauzer Lizards running faster than their little legs could carry them? No wonder fossils were never found.

  5. 5
    Joe says:

    Schnauzers evolved from Schnauzer lizards, duh. 😎

  6. 6
    wd400 says:

    No wonder fossils were never found.

    You sure about that, really sure?

    (Modern lizard also show almost every stage from limb-reduction to complete loss of legs, FWIW)

  7. 7
    ppolish says:

    WD, the gist of the article quoted in the OP suggests Najash sprouted rear legs instead of losing its fronts. That is the new knowledge added by the study.

  8. 8
    wd400 says:

    Well, the press release is, as ever, pretty sloppy.But that’s not at all what the paper says.

  9. 9
    ppolish says:

    Ok, my mistake WD.

  10. 10
    rvb8 says:

    ‘atavism’ can occur in snakes, just as whales sometimes grow a perfectly useless leg. The gene expression remains, and is a clear indicator of a shared ancestor.

  11. 11
    ppolish says:

    Rvb8, a modern four legged snake is a marvel of Design, not a result of Evolution. Kind of cute too – for a snake:

    http://m.youtube.com/watch?v=S0EsxmCi4LU

  12. 12
    Robert Byers says:

    AHA. It shows how evolutionism is speculative. POF like that its now snakes didn’t loss their legs but the others grew them.
    Oh brother.
    The bible says the snakes lost their legs. They find bits remaining in big snakes of firmer hips. Another poster here said they sometimes have a leg at birth.
    Snakes are amongst the few creatures with anatomical evidence of a actual former different body type.
    So they didn’t start out legless.

  13. 13
    Zachriel says:

    Robert Byers: POF like that its now snakes didn’t loss their legs but the others grew them.

    No. In terms of the hox genes, snakes didn’t lose their legs, but have modified them.

    Robert Byers: It shows how evolutionism is speculative.

    No, it’s called evidence.

  14. 14
    Robert Byers says:

    Zachriel
    They would of said the first conclusion was based on scientific evidence and now they would say it was wrong! Was the science methodology wrong?
    They would of said creationists are wrong to deny the science in order to prove genesis! now they deny that “former” science.
    Somebody was wrong or science is wrong.
    The truth is that it is speculative based on trivial data.
    Thats why the conclusions change with a few minor more researchers.
    Thats evolutionary biology.
    Its not a scientific investigation.
    Its not using a higher standard of investigation including using actual evidence.
    thats why this was a great thread.
    It makes our point.
    not just the snakes don’t have a leg to stand on.

  15. 15
    Zachriel says:

    Robert Byers: They would of said the first conclusion was based on scientific evidence and now they would say it was wrong!

    Actually, both hypotheses had been proposed, and there was no definitive evidence, hence the study.

    The origin of the snake-like body form, with its deregionalized pre-cloacal axial skeleton, has been explained as either homogenization of Hox gene expression domains, or retention of standard vertebrate Hox domains with alteration of downstream expression that suppresses development of distinct regions. Both models assume a highly regionalized ancestor, but the extent of deregionalization of the primaxial domain (vertebrae, dorsal ribs) of the skeleton in snake-like body forms has never been analysed.

  16. 16
    Robert Byers says:

    Zachriel.
    i protest. its likely some offered another option but the herd and the trumpet on snake legs wherever talked about was about them losing legs.
    It was a conclusion of SCIENCE. a few critics don’t change what was the conclusion.
    Now they changed the conclusion and one must ask WHY WAS THE SCIENCE WRONG? Hoc could scientists be wrong? Creationists are told don’t question SCIENCE. ScIENCE can’t be wrong.
    whopps there it goes.
    i think there is just people thinking about things.
    Science is a lame word for a higher standard of investigation.
    its only a higher standard if it is. Calling it sCIENCE is not proof is was done with the higher standard.
    evolutionary biology is case in point.
    Evo bio has NO bioSCI evidence for itrs great claims.
    if they do then list the top three or one.

  17. 17
    Zachriel says:

    Robert Byers: i protest. its likely some offered another option but the herd and the trumpet on snake legs wherever talked about was about them losing legs.

    Their ancestors had legs, if that is your concern. The scientific question was whether they lost the molecular patterning or whether the molecular patterning was modified.

  18. 18
    Joe says:

    Their ancestors had legs, if that is your concern.

    That could be but science has yet to demonstrate such a thing.

  19. 19
    ppolish says:

    I thought their ancestors were once fish? Legless fish. Legs come legs go, legs come legs go. Many many leg designs.

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