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Author Topic:   Archaeopteryx and Dino-Bird Evolution
extremophile
Member (Idle past 5703 days)
Posts: 53
Joined: 08-23-2003


Message 66 of 200 (302724)
04-09-2006 9:24 PM


very interesting thread. I that in this forum some times the thing turns out from creationism and deals with real science in a way that is a bit hard to find usually in aonther forums...
Anyway, somewhere someone said about the possibilty of a very early origin of feathers, if Longisquama really possessed feathers. But then feathers on present day birds (i’m not saying that Longisquama would be a bird, I’m out of the taxonomical arguments) would be a sort of reactivation of long-disabled genes. But would not had been these genes disabled for way too long time? They could have been preserved by alternative splicing or something else, anyway, but seems odd to me. Also, if Longisquama were really feathered, which other predictions on the distribution of feathers could be done? Closely related groups should also have feathers in different stages, should not them?
About secondary flightlessness, where the supporters of this hypothesis place exactly the dromaeosaurs that would be birds? I’ve found once proposed "cladogram", which placed them after Archaeopteryx, but is this a necessary assumption of the hypothesis?
A bit related to that was the creationist claim that could be that Archie was a good flier. Actually he was not, but I think that even if he was, it does not take the transitional status from him. But the relation with the earlier issue... there is a possibility that Archaeopteryx is rather than a species in which avian flight is just beginning, a descendant from an unknown bird with more developed flight?
Other point a bit related is on warm-bloodness of dinosaurs. It was the first time I read that they might be all warm blooded, and as far as I heard of the implications of that, it sounds a bit difficult to be true. Such as the ammount of food required for sustain a high metabolism in large sauropods. Also, I found much interesting the nearly extreme opposite point of view, that not even the early birds would be as warm-blooded as the present day birds. I’ve read a paper on that some time ago, but sadly I can’t remember anything. A bit consistent with that hypothesis, or at least seems to me, is the state of the Alvarezsaurids, if considered as flightless birds, the nature of their anatomy and comparison with the loss of flight in present day birds.
It’s explained more detailed here in the site palaeos.com
Palaeos: Page not found
Other interesting thing in this whole topic in general, is that Archaeopteryx, accoriding with some recent studies, is yet more dromaeosaur than ever. First, no reversed halux; also, he’d have had the sickle claw too. Something else I don’t know exactly in the anatomy of the head was also more similar to dromaeosaurs than what was previously known.
Also about the sickle claws, I’ve read recently (I guess was on DML) the suggestion that these could have been used as a climbing tool rather than as a weapon of any kind. If archie has them, it makes a lot of sense, or so it appears to me. Maybe they could make comparisons on how the size of these claws vary from species to species according to weight of the animal. But anyway it does not impedes that after reaching some size the claws were used as weapons, since is a bit weird to picture Utahraptor climbing in a trunk.

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extremophile
Member (Idle past 5703 days)
Posts: 53
Joined: 08-23-2003


Message 68 of 200 (302956)
04-10-2006 1:50 PM
Reply to: Message 40 by arachnophilia
02-15-2006 10:26 PM


scutes
birds grow feathers on their feet, instead of scutes. scutes are the second type of scale that a bird has. the first is very reptilian, but scutes are genetically and chemically the same as feathers, made of keratin. and that's because they're actually derived from feathers. the issue here is that we know dinosaurs had scutes.
the problem is that it's not just the theropod dinosaurs that have scutes, either. anklysaurs had them. which means that the genetic code for feathers existed before the saurischia/ornithischia divide. so the only dinosaurs that didn't have feathers are the ones that lost them, due to size or further adaptation. this also explains microraptor (above) quite nicely. it had the genetic code for feathers on its feet (like modern birds) but lacked or contained defective copy of the code to turn those feathers into scutes.
But probably there are those who deffend that inversely feathers are derived from scutes, or that is out of question? Or, alternatively, could be that scutes derive from a simpler, onthological "common ancestor" of advanced feathers, not being necessarily an "aborted" advanced feather?
This message has been edited by extremophile, 04-10-2006 03:51 PM

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 Message 40 by arachnophilia, posted 02-15-2006 10:26 PM arachnophilia has replied

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extremophile
Member (Idle past 5703 days)
Posts: 53
Joined: 08-23-2003


Message 70 of 200 (303977)
04-13-2006 3:40 PM
Reply to: Message 69 by arachnophilia
04-10-2006 9:26 PM


feathers, scutes, etc
BBC NEWS | Science/Nature | Feathered embryo found in China
May be of some interest on the issue of origin of feathers. The earliest known fossil of bird embryo, had fully formed feathers, whereas most of the arboreal birds today born featherless
...
Does someone knows which bird is being mentioned at the end of the article? It is "four winged" like Microraptor, but it is an enantiornithinefrom early Cretaceous.
This message has been edited by extremophile, 04-13-2006 05:43 PM

"Science comits suicide when it adopts a creed."
Thomas H. Huxley

This message is a reply to:
 Message 69 by arachnophilia, posted 04-10-2006 9:26 PM arachnophilia has replied

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