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Mobile beak in bird fossil forcing relook at bird evolution

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  • Mobile beak in bird fossil forcing relook at bird evolution

    A tiny 67 myo fossilized broken bone, unearthed in a quarry outside of Liège, Belgium in 2002, may cause a rewriting of how we think bird evolution progressed. Most modern birds have a jointed upper jaw which permits the upper half of their beak to move, but some, like emus, ostriches and rheas, have fused upper palates meaning that he top portion of the beak is far less mobile.

    This fused palate is also found in dinosaurs, including the feathered ones that were ancestors to birds around today. This led researchers to conclude that birds such as emus and the like evolved first and that the mobile upper beak was a later development.

    Source: 67-million-year-old fossil upends bird evolutionary tree


    Beak bone from ancient bird revises order of their modern ancestors.

    A prehistoric toothed bird that lived 67 million years ago is turning the bird tree of life on its head. The bird — named Janavis finalidens — shares crucial features with its modern cousins such as chickens and ducks, which is forcing a rethink about bird evolution1.

    A stone-encased fossil was plucked from a Belgian quarry two decades ago2. It was found in a geological layer that dates back to the Late Cretaceous period (100.5 million to 66 million years ago), just before the mass extinction event that wiped out all non-avian dinosaurs. At the time of the fossil’s discovery, it seemed to comprise just a handful of bones from the spine, wings, shoulders and legs.

    Daniel Field, a palaeontologist at the University of Cambridge, UK, and his colleagues re-examined the bones using micro-computed tomography to better investigate the creature’s anatomy. From those scans, they were able to describe the specimen as a new species of ancient bird that shared a common ancestor with modern birds. When it lived, Janavis finalidens would have been similar in size to a grey heron. The study is published in Nature today.

    The team also discovered that one of the bones, previously thought to be a shoulder bone, was actually from the skull — a bone called the pterygoid. “It is from a very interesting part of the skull, from the bony palate of the bird,” says Field. The bony palate has crucial features that researchers use to group birds, both living and extinct.


    An ancient split

    Most of the world’s 11,000 bird species belong to a group called the neognaths, or ‘new jaws’. Key bones in the neognath palate are mobile, allowing the birds to move their upper beak independently from their skull. A much smaller group of birds including the flightless emu, cassowary, ostrich, kiwi and the flighted tinamous, make up the palaeognaths, or ‘ancient jaws’. The bones in their upper palate — including the pterygoid — are fused together.

    As their names suggest, it has long been assumed that the ancient-jawed palaeognaths appeared first and the neognaths descended from a palaeognath ancestor, after the last common ancestor of all modern birds lived some 80 million years ago, says Field. In part, this is because non-avian dinosaurs that pre-date modern birds also have fused palates.

    That assumption has been hard to test because the small, delicate pterygoid is usually missing from fossils, says Thomas Stidham, a palaeontologist who studies bird evolution at the Chinese Academy of Sciences in Beijing.

    Janavis’s pterygoid probably formed part of an unfused bony palate, meaning the bird's upper beak was mobile. Its resemblance to the unfused pterygoids of modern chickens and ducks suggests that neognaths’ mobile beaks evolved first, and palaeognaths’ fused beaks arose later, says Field.

    “It’s a reverse way of looking at things to what we often have been assuming,” says vertebrate palaeontologist Trevor Worthy at Flinders University in Adelaide, Australia.

    One question that remains, says Stidham, is how the unfused palate of species such as Janavis evolved from their fused-palate dinosaur ancestors. He says that bird fossils from the early Cretaceous — if they have preserved pterygoids — could hold to answer that question.

    Form and function

    Bones of the upper palate are crucial for bird beaks’ function, says Gerald Mayr, a palaeornithologist from the Senckenberg Research Institute and Natural History Museum in Frankfurt, Germany. The unfused palate of neognaths “increases the flexibility of the beak and improves the use of the beak as a tool”, he says.

    If palaeognaths are derived from a neognath ancestor, it is unclear why they developed the fused palate structure that emus, ostriches and kiwis bear today. “There’s no obvious reason for that if the other morphology is more advantageous,” says Mayr.

    Fused palates aren’t necessarily a drawback, says Stidham, and could give beaks of larger birds additional support. Although the structures differ, “the function is basically the same”, he says, and both versions are able to flex and transfer force towards the beak tip.

    Whatever their purpose, the fused palate in modern palaeognaths could be a case of convergent evolution, says Field. Flightlessness evolved independently in emus and ostriches, which sit on different branches of the modern palaeognath tree, he says. It’s possible that those lineages also evolved fused palates independently.

    Field and his colleagues will test this hypothesis by looking at the early developmental stages of modern palaeognaths. If there are different ways of forming a fused palate, that could indicate that the trait arose independently on several occasions.



    Source

    © Copyright Original Source



    The full paper is Cretaceous ornithurine supports a neognathous crown bird ancestor, which can be accessed by request from Accepted version (Unknown, 172Kb), although here is the abstract from it:

    Abstract

    The bony palate diagnoses the two deepest clades of extant birds: Neognathae and Palaeognathae1,2,3,4,5. Neognaths exhibit unfused palate bones and generally kinetic skulls, whereas palaeognaths possess comparatively rigid skulls with the pterygoid and palatine fused into a single element, a condition long considered ancestral for crown birds (Neornithes)3,5,6,7,8. However, fossil evidence of palatal remains from taxa close to the origin of Neornithes is scarce, hindering strong inferences regarding the ancestral condition of the neornithine palate. Here we report a new taxon of toothed Late Cretaceous ornithurine bearing a pterygoid that is remarkably similar to those of the extant neognath clade Galloanserae (waterfowl + landfowl). Janavis finalidens, gen. et sp. nov., is generally similar to the well-known Mesozoic ornithurine Ichthyornis in its overall morphology, although Janavis is much larger and exhibits a substantially greater degree of postcranial pneumaticity. We recovered Janavis as the first-known well-represented member of Ichthyornithes other than Ichthyornis, clearly substantiating the persistence of the clade into the latest Cretaceous9. Janavis confirms the presence of an anatomically neognathous palate in at least some Mesozoic non-crown ornithurines10,11,12, suggesting that pterygoids similar to those of extant Galloanserae may be plesiomorphic for crown birds. Our results, combined with recent evidence on the ichthyornithine palatine12, overturn longstanding assumptions about the ancestral crown bird palate, and should prompt reevaluation of the purported galloanseran affinities of several bizarre early Cenozoic groups such as the ‘pseudotoothed birds’ (Pelagornithidae)13,14,15.



    3 minute long video on the discovery


    I should note that an article in Science regarding this concludes with

    Several skulls of its older Ichthyornis relative have been described in recent years with bones that suggested the bird’s upper palate might have been jointed, but the evidence was still fuzzy. Now, in the Janavis fossil, “the specific skull bone that materialized was the particular one we needed” to show the upper beak was flexible, Field says. Torres agrees. “It’s like a puzzle where that one piece was missing, and now we have it,” he says.


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  • #2


    Tilda.jpg
    Speaking of mobile beaks - the one and only "Tilda."
    1Cor 15:34 εκνηψατε δικαιως και μη αμαρτανετε αγνωσιαν γαρ θεου τινες εχουσιν προς εντροπην υμιν λεγω
    Come to your senses as you ought and stop sinning; for I say to your shame, there are some who know not God.
    .
    If Palm Sunday really was a Sunday, Christ was crucified on a Thursday (which could be adduced from the gospels anyway).

    "The synoptic gospels claim that Jesus was crucified on the 15th day of Nisan and buried on the 14th day of Nisan:" Majority Consensus

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    • #3


      Look a bit like siblings.

      Except for the teeth

      And more robust legs

      And webbed feet

      Other than that...


      I'm always still in trouble again

      "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
      "Overall I would rate the withdrawal from Afghanistan as by far the best thing Biden's done" --Starlight
      "Of course, human life begins at fertilization that’s not the argument." --Tassman

      Comment


      • #4
        Originally posted by rogue06 View Post


        Look a bit like siblings.

        Except for the teeth

        And more robust legs

        And webbed feet

        Other than that...
        Tilda likely had the gene for teeth.
        Glendower: I can call spirits from the vasty deep.
        Hotspur: Why, so can I, or so can any man;
        But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

        go with the flow the river knows . . .

        Frank

        I do not know, therefore everything is in pencil.

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