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Thread: New dinosaur fossil challenges bird evolution theory

  1. #1 New dinosaur fossil challenges bird evolution theory 
    Forum Sophomore laza's Avatar
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    The discovery of a new bird-like dinosaur from the Jurassic period challenges widely accepted theories on the origin of flight. Co-authored by Dr Gareth Dyke, Senior Lecturer in Vertebrate Palaeontology at the University of Southampton, the paper describes a new feathered dinosaur about 30 cm in length which pre-dates bird-like dinosaurs that birds were long thought to have evolved from.
    Over many years, it has become accepted among palaeontologists that birds evolved from a group of dinosaurs called theropods from the Early Cretaceous period of Earth's history, around 120-130 million years ago. Recent discoveries of feathered dinosaurs from the older Middle-Late Jurassic period have reinforced this theory.
    The new 'bird-dinosaur' Eosinopteryx described in Nature Communicationsthis week provides additional evidence to this effect.
    "This discovery sheds further doubt on the theory that the famous fossil Archaeopteryx -- or "first bird" as it is sometimes referred to -- was pivotal in the evolution of modern birds," says Dr Dyke, who is based at the National Oceanography Centre, Southampton."Our findings suggest that the origin of flight was much more complex than previously thought."
    The fossilised remains found in north-eastern China indicate that, while feathered, this was a flightless dinosaur, because of its small wingspan and a bone structure that would have restricted its ability to flap its wings.The dinosaur also had toes suited to walking along the ground and fewer feathers on its tail and lower legs, which would have made it easier to run.

    the source is e! Science News


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    WYSIWYG Moderator marnixR's Avatar
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    here'a few links to commentary in the press

    Eosinopteryx feathered dinosaur offers clues on bird evolution
    Eosinopteryx brevipenna • Reduced plumage and flight ability of a new Jurassic paravian theropod (Theropoda: Troodontidae) from China
    Wikipedia

    does it totally rewrite our understanding of bird evolution ? i doubt it very much
    it's still clear that a variety of theropods had feathers and other bird-like features, and over the years there's been a growing suspicion that archeopteryx may just be a side branch not directly leading to birds
    no doubt further finds will enlighten us over the exact route to modern birds (and flight ? although the latter could be a different thing)

    on thing's for sure though : feathers no longer define birds, and that has been the case for a number of years now


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    WYSIWYG Moderator marnixR's Avatar
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    looking at the synopsis of the Nature article "Reduced plumage and flight ability of a new Jurassic paravian theropod from China", it's clear that the rewrite of the evolution of birds and flight is a little more involved than the headlines in the popular press suggest (nothing new there)

    especially the quote

    Eosinopteryx increases the known diversity of small-bodied dinosaurs in the Jurassic, shows that taxa with similar body plans could occupy different niches in the same ecosystem and suggests a more complex picture for the origin of flight.
    basically "Phylogenetic hypotheses including these specimens have challenged the pivotal position of Archaeopteryx in bird phylogeny" just means that the picture is a little bit more complicated than that the evolution of feathers, flight and birds started with Archaeopteryx
    the predominance of early cretaceous bird-like dinosaurs and dinosaur-like birds is surely purely an artefact from exceptional preservation in China during that period - it doesn't say anything about whether birds only came into their own in the early Cretaceous

    as for having dinosaurs older than Archaeopteryx with clearly bird-like features, that has been expected for some time, seeing as the diversity in the early Cretaceous is already massive
    it may only be a matter of time before Archaeopteryx is downgraded to a very bird-like deinonychosaur
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    I've been curious how forelimbs such as those possessed by T-Rex or Veloceraptors even evolved in the first place. What use would they be with such a limited range of motion? Just tearing flesh up to eat it?

    Especially the raptors' forelimbs look like atrophied wings, rather than purpose grown forelimbs.



    Velociraptor - Wikipedia, the free encyclopedia





    It's just weird to think that wings came second.

    Or did they? Could wings have come first, but originally only been used for some limited purpose, like the purpose they serve for Ostriches? More for stability and control while running or something like that, and then (for raptors) they moved toward claws? And (for birds) gradually became actual tools for flight?
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    Feathers came first from what I understand.

    As for those short forelimbs, look at the kangaroo. They rarely use them much though they're probably well integrated into balancing while jumping. They're handy, dandy for fighting though.
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    WYSIWYG Moderator marnixR's Avatar
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    maniraptor forelimbs are not short - maybe shorter than your standard bird but definitely of standard length for a dinosaur that size
    it only appears to be the biggies like T.rex, Carnotaurus and Giganotosaurus that seems to have shrunk front limbs

    in addition, "Maniraptorans are united by the possession of modified elements in the wrist; the semilunate carpal is a bone unique to this group — along with other modifications of the forelimb, it makes the flight stroke in birds possible, and was probably co-opted by birds for flight from a grasping function." (see Berkeley site)
    so in essence they were already capable to move the forelimb in such a way that foreshadowed the movements of birds when they fly, say for snatching prey on the run or or balancing while making sharp turns on the run
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    Pet theory of mine is that feathers initially served for egg incubation. Because feathers were sexual features, they were objects of sexual selection and in some species developed far beyond original utility - they could even be an encumbrance. A few of these excessively feathered species meanwhile adapted to nest in the safety of trees and cliffs. Now picture such a creature spreading its plumage to attract mates, wobbling precariously atop the highest nesting site it could claim...
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    WYSIWYG Moderator marnixR's Avatar
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    presumably you're thinking of the oviraptor on its nest ?

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    If I'm not mistaken, feathers are thought to first appear in the crotch, and downy ones at that. Surely those were "setting" feathers?

    Pure speculation on my part that some dinosaurs nested in trees or cliffs. That's just a leg up on gliding, on the way to flight.

    What would you say to that grasping maniraptoran forearm a climbing adaptation?
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    WYSIWYG Moderator marnixR's Avatar
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    oviraptor was pretty late in the scheme of things and is known to have had ast least down cover + display feathers (not sure if there's adequate evidence for pennate feathers on the forearms)
    the grasping arm would have been a pre-adaptation to the movements involved in flight, and would have been useful on the ground as well, e.g. for manoeuvrability like a road runner, or for jumping up at insects
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  12. #11  
    Forum Radioactive Isotope Paleoichneum's Avatar
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    Quote Originally Posted by Pong View Post
    If I'm not mistaken, feathers are thought to first appear in the crotch, and downy ones at that. Surely those were "setting" feathers?

    Pure speculation on my part that some dinosaurs nested in trees or cliffs. That's just a leg up on gliding, on the way to flight.

    What would you say to that grasping maniraptoran forearm a climbing adaptation?
    You need to take a look at the Middle Jurassic forms and go from there. Its possible that the split leading to coelurosaurians (and thus modern birds) was soon after the emergence of Dinosauria in the early Triassic.
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