Archaeopteryx and Dino-Bird Evolution

flying birds, yes. flightless birds tend to be much shorter, but the evidence is that they evolved from flying birds (though, i believe, there are some crazies that suspect paleognaths came straight from dinos). anyways, longer arms is evidence of avian tendencies. the shortest, actually. except maybe mononykus, but i can never get a straight answer on whether or not that's a chimera.dromaeosaurs and troodondits have the longest arms, and archaeopteryx holds the record, with arms and legs equal in length. velociraptor has the longest arms of any dinosaurs that's not actually a bird, iirc.

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eight if you count the feather. one year flood.

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there is no "reptilia." it's sauropsida. sauropsids and reptiles are synonymous, and the term "reptile" was actually discarded in terms of cladistics some time ago, because dinosaurs abd birds (sauropsids) don't fit especially with the connotation of "reptile."

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oh, ok, i must have missed that.we know there was secondary feather loss on the feet, because of genetics.

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yes, yes, i was unaware of that find. but thanks for pointing it out.do you think this rules out the dinosaur having feathers? just complicates the matter? any particular take on this? it's rather peculiar that other closely related dinosaurs (both branching lower and higher on the tree, cladistically) did have feathers.

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well, the thing is this. we know that at some point dinosaurs/birds lost some feathers. the earliest flying dinosaurs we have are "four-winged," with flight feathers on their feet. genetically, we know that modern bird scutes evolved from feathers.so the question i'm really asking is, is it safe to say that juravenator probably had feathers, and this secondary feather adaptation? i'm not sure, they note that the skin lacks the follicles for feathers. it might an age/gender thing?or maybe the simplest deduction is that feathers are convergent. [or reccessive?]Edited by arachnophilia, : added bracket

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more info:

quote:

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Birds have scales and feathers needn't always cover the remainder of the body. The preservation of feathers in Juravenator's nearest relative known to have feathers, Sinosauropteryx is apparently limited to a mindline "mane" of filaments, an may not necessarily have covered the bodies. Whether or not this was the true condition in life could, potentially, be disputed. However, it follows from the enormous diversity of theropod dinosaurs that their feather distributions (both within and among taxa) were considerably more varied than previously though.

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Tyrannosaurs are known to have patches of scaly skin, but recent discoveries show that their ancestors probably had feather-like structures. Thus, at some point, feathers must have been either incompletely covering the animal or lost and gained over varying degrees. Moreover, it appears that estimates of feather covering in dromaeosaurs were dramatically underestimated It would appear that our interpretation of feather evolution paints, perhaps too conservatively rather broad coating of feathers on just about anything descended from the common ancestor of all coelurosaurian dinosaurs.

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Xing Xu, who has described many of the Chinese feathered dinosaurs, wrote a News and Views piece which raised some interesting cautions about these results: For one, we don't know that Juravenator did not have feathers. All we know is that parts of its body had scales. Fossilization is biased against feather preservation and those few records we have are remarkably rare. The specimen is apparently a juvenile and may, in fact, create a false signal pulling the animal to a particular part of the tree. Normally, this would be the other way around: juvenile characters tend to make you look more 'primitive'. However, Juravenator clumps with a group of small theropod dinosaurs which may share character similarities simply related to the fact that they're small, and not any real common ancestry. It's possible that this animal is more primitive, but unites with these other animals due to bias.

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source

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hmm.

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yeah, i got curious, and googled. i still don't quite know what to make of it. very peculiar.

since anglagard brought it up in the gd, please read my previous response to you, on archaeopteryx and forgery. you don't have to respond to it here (continue your forgery discussion with anglagard in the gd), but at least look it over and try to understand why aig says this is an argument creationists should not use.

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this is actually somewhat old news. archie's flight feathers on his leg do not extend all the way down his feet, like microraptor.we've also had some discussion here before on how microraptor would have flown. the "splayed" model is anatomically impossible, but i suspect the "biplane" model is aerodynamicall untennable. i've heard some suggestion that the leg-wings which have been used as vertical surfaces, like rudders.

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yes, it's a very complex picture, expecially since microraptor lived some 20 million years after archaeopteryx.

quote:

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Longrich speculates that the hindlimb feathers might have served other roles in addition to flight. Like modern pigeons, kittiwakes and vultures, Archaeopteryx's hindlimb feathers might have acted as airbrakes, or perhaps stabilizers, control surfaces or flaps, Longrich writes.

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(from the article linked above)

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i think that function is probably more likely, especially for archaeopteryx.

quote:

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Scientists don’t know when in their evolutionary history birds switched from a "four winged" design to a two-wing one, but it's thought that hindlimb wings were sacrificed in order to free up legs for other functions, such as running, swimming and catching prey.

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there's an interesting idea that's looking more and more valid all the time -- that the idea of "fling birds" and "running dinosaurs" are a bit more convuluted than previously thought. meaning that early dinosaurs took to the air far sooner than previously thought, and subsequently lost flight capabalities, only to re-evolve them.there are many things we are calling "birds" that have a good number of dinosaurian characteristics that archaeopteryx lacks, and vice-versa. as suggested earlier in this thread, it's quite possible that some of the especially avian maniraptorian dinosaurs might have actually evolved from something like archaeopteryx. so it might be right to call velociraptor a flightless bird, under the current thought. essentially meaning that our current colloquial usage of "bird" describes a polyphyletic group, composed of many groups that independently evolved from the dinosaurian line. it would certainly explain the "opposite birds."

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