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Sharks not primitive? Well, if they aren’t, what is?

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proposed evolution of fish/Oxford University, K Trinajstic

From ScienceDaily:

An investigation of a 415 million year-old fish skull strongly suggests that the last common ancestor of all jawed vertebrates, including humans, was not very shark-like. It adds further weight to the growing idea that sharks are not ‘primitive’.

Has anyone ever defined what it means for a life form to be “primitive”? How easy is it for any life form to just randomly originate?

Chondrichthyans [cartilaginous fishes, like sharks] have often been viewed as primitive, and treated as proxies for what the ‘ancestral’ jawed vertebrate would have looked like. A key component of this view is the lack of a bony skeleton in cartilaginous fishes.

‘The results from our analysis help to turn this view on its head: the earliest jawed vertebrates would have looked somewhat more like bony fishes, at least externally, with large dermal plates covering their skulls,’ said Sam Giles of Oxford University’s Department of Earth Sciences, first author of the report. ‘In fact, they would have had a mix of what are now viewed as cartilaginous- and bony fish-like features, supporting the idea that both groups became independently specialised later in their separate evolutionary histories.’

So the researchers think that sharks were originally bony, and that the cartilaginous stuff was an adaptation:

The team then used X-ray CT (computed tomography) to ‘virtually’ cut through the fossil. Different materials attenuate X-rays to different amounts — just as in a hospital X-ray, bones show up brighter than muscles and skin. This same principle can be applied to fossils, as fossilised bone and rock attenuate X-rays to different degrees. This technique was used to build a 3D virtual model of the fossil, enabling its internal and external features to be examined in great detail. Traces left by networks of blood vessels and nerves, often less than 1/100th of a centimetre in diameter, could then be compared to structure in a variety of jawed vertebrate groups, including sharks and bony fishes.

‘Losing your bony skeleton sounds like a pretty extreme adaptation,’ said Dr Friedman, ‘but with remarkable discoveries from China, Janusiscus strongly suggests that that the ancient ancestors of modern sharks and their kin started out just as ‘bony’ as our own ancestors.’

So, readers, which multicellular life forms can genuinely claim to be “primitive”? What must a life form do to be “primitive” and still be life?

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9 Replies to “Sharks not primitive? Well, if they aren’t, what is?

  1. 1
    Mung says:

    Sharks evolved to eat non-sharks. It follows that non-sharks are more primitive.

  2. 2
    wd400 says:

    So, readers, which multicellular life forms can genuinely claim to be “primitive”? What must a life form do to be “primitive” and still be life?

    They’d have to be like their ancestors. Very few species are uniformally random (even so called “living fossils” have plenty of derrived traits) so evolutionary biologists don’t usually use the term to describe species (rather particular traits of species).

  3. 3
    rvb8 says:

    A 415 million year old fossil was found with, ‘a mix of what are now viewed as cartilaginous- and bony fish-like features, supporting the idea that both groups became independently specialised later…’.

    This is merely a corroboration of what evolution predicts. The, ‘large dermal plates’ is the giveaway, fish nor sharks have these today, but the 415 million year ancestor did. Further, it bequeathed its ‘cartilaginous’ anatomy to its descendent sharks, and its ‘bony fish-like features’ to modern fish; where’s the confusion?

  4. 4
    franklin says:

    The, ‘large dermal plates’ is the giveaway, fish nor sharks have these today, but the 415 million year ancestor did

    Sturgeon have retained these dermal plates in what are known as scutes. They (the scutes) represent the only bone found in these fishes bodies. They date back to around 200 mya.

  5. 5
    Robert Byers says:

    its a old Darwin evolution myth that this or that creature was more primitive because of this or that.
    In fact god created everything brilliant. Nothing primitive.
    If so primitive then mANKIND just do in from raw materials.

  6. 6
    rvb8 says:

    Thanks franklin, you are quite right. I feel a little foolish. However my post remains accurate. This ancestral fish possessed two traits that branched into two lines.

  7. 7
    Andre says:

    This ancestral fish possessed two traits that branched into two lines.

    Or like any good designer a mix of engineering solutions to specific engineering problems, we call them trade-offs

    http://www.design.caltech.edu/.....02_90e.pdf

  8. 8
    Joe says:

    Sturgeon have retained these dermal plates in what are known as scutes. They (the scutes) represent the only bone found in these fishes bodies. They date back to around 200 mya.

    Today’s sturgeons are just as evolved as we are.

  9. 9
    Joe says:

    Whatever a primitive life-form is it has to be able to synthesize all of the essential biomass molecules. And that is why an unguided OoL is not even feasible.

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