Thursday, February 23, 2012

Aviremigia

It is possible to be more precise about the point where pterosaurs developed into primitive birds. I have been saying (for simplicity) that that point is the appearance of maniraptors. But not all taxa that are labeled "maniraptor" are birds. (For example, members of Ornitholestes are not birds).
At least the "maniraptors" from the paraves/oviraptors to the present, are birds. They are called Aviremigia.
Also called Chuniaoae.

Here is Naish:
http://scienceblogs.com/tetrapodzool..._they_dont.php

Quote:
The fact that long remiges have now been documented in oviraptorosaurs, dromaeosaurids and other maniraptorans shows that feathered arms essentially the same as those present in basal birds evolved somewhere round about the base of the oviraptorosaur + paravian clade, and there is no evidence that wing-like arms were present in more basal coelurosaurs, nor in other theropods, or other dinosaurs, or other archosaurs.

13 comments:

  1. Comment received:
    Did you change your sidebar? Do you now consider some Maniraptors dinosaurs?

    ReplyDelete
  2. I posted above:
    "Basically the maniraptors before the paraves/oviraptors are not primitive birds."

    We do not need to concern ourselves with what those other "maniraptor" creatures were. They are not on the pterosaur to bird line.

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  3. When you write:

    "The category called "theropod dinosaurs" should include only the actual dinosaurs (eg. Tyrannosauroidea etc) and not most of the creatures labeled "maniraptors""

    It implies that there are some maniraptor theropod dinosaurs which you most certainly do need to concern yourself with as it would mean maniraptors evolved multiple times from completely different lineages, from dinosauria and from pterosauria.

    So perhaps you should clarify what exactly the non-primitive maniraptors are or change the wording on your sidebar.

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  4. The label "maniraptor" is just a label. The creatures included in that label are of two completely different kinds.
    The aviremigia developed from pterosaurs.
    We do not need to concern ourselves with the others. Perhaps they are dinosaurs. But it does not matter.
    I do not think the sidebar is a problem.

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  5. How about I update the sidebar to say:
    Most of the creatures labeled "maniraptor" (those from Aviremigia to the present) are not dinosaurs but primitive flying, and secondarily flightless, birds, within the separate bird line.

    ReplyDelete
  6. Are ornithomimosaurs dinosaurs now then?

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  7. There seem to be a number of creatures that may be primitive secondarily flightless birds. The following are possibilities (but I have not done much research):
    Ornithomimosaurs (at least some in this category)
    Therizinosaurs
    Alvarezsaurids
    Oviraptors

    If we look at modern flightless birds we see:
    Ostrich (Struthio), Rhea (Rheidae), Cassowary, Emu (Casuariidae), Kiwi (Apteryx) and Tinamous.

    These creatures look quite different from each other so possibly they have different lineages from different primitve flightless bird lines.

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  8. It does not look like Therizinosaurs were flightless birds. Concerning feathers here is what wikipedia says:
    "Skin impressions from Beipiaosaurus indicate that therizinosaurs were covered with a coat of primitive, down-like feathers similar to those seen in the compsognathid Sinosauropteryx, as well as longer, simpler, quill-like feathers that may have been used in display.[2][3]".

    The so-called "downy feathers" were decayed skin.

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  9. Concerning alvarezsaurs a case could be made that they are flightless birds:
    http://en.wikipedia.org/wiki/Alvarezsauridae
    "... assignments of alvarezsaurs to birds were caused primarily by features that are strikingly, or even uniquely, avian. The sternum, for example, is elongated and deeply keeled for an enlarged pectoralis muscle, as it is in neognathous birds and volant ratites. One bone in the skull of Shuvuuia appeared to be an ectethmoid fused to a prefrontal. The ectethmoid is an ossification known only in Neornithes. Other birdlike characters included the palatine, foramen magnum, cervical and caudal vertebrae, and many others.[9]

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  10. Ornithomimosaurs may be flightless birds.
    http://www.nhm.ac.uk/nature-online/life/dinosaurs-other-extinct-creatures/ostrich-dino-article/index.html

    "All members of this group [Ornithomimosaurs] bear a striking resemblance to some of the large flightless birds that are alive today, such as ostriches and emus. Ornithomimosaurs, like ostriches, had long graceful necks, small heads with a beak-like snout, very long legs (which allowed them to run at up to 60 km per hour) and a slender tail."

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  11. Some initial info:
    http://en.wikipedia.org/wiki/Maniraptora
    "Maniraptora is the only dinosaur group known to have included flying members, though how far back in this lineage flight extends is controversial. Powered and/or gliding flight is believed to have been present in some types of dromaeosaurid, such as Rahonavis and Microraptor.[5] Other groups, like the Oviraptorosauria, are not known to have been capable of flight, but some scientists have suggested that they could be descended from ancestors which flew. Paul has suggested that this might be the case. Paul has gone as far as to propose that Therizinosauria, Alvarezsauroidea, and the non-maniraptoran group Ornithomimosauria descended from flying ancestors as well.[6]"

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  12. Oviraptors as flightless birds:
    http://en.wikipedia.org/wiki/Oviraptorosauria

    "Analyses like those of Osmólska et al. (2004) suggest that they [Oviraptors] may in fact represent primitive flightless birds".[2]

    "Evidence for feathered oviraptorosaurs exists in several forms. Most directly, four species of primitive oviraptorosaurs (in the genera Caudipteryx, Protarchaeopteryx, and Similicaudipteryx) have been found with impressions of well developed feathers, most notably on the wings and tail, suggesting that they functioned at least partially for display. Secondly, at least two oviraptorosaur specimens (Nomingia and Similicaudipteryx) preserved tails ending in something like a pygostyle, a bony structure at the end of the tail that, in modern birds, is used to support a fan of feathers.[5] Similarly, quill knobs (anchor points for wing feathers on the ulna) have been reported in the oviraptorosaurian species Avimimus portentosus.[7] Additionally, a number of oviraptorid specimens have famously been discovered in a nesting position similar to that of modern birds. The arms of these specimens are positioned in such a way that they could perfectly cover their eggs if they had small wings and a substantial covering of feathers.[8]"

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