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Author Topic:   Archaeopteryx and Dino-Bird Evolution
DBlevins
Member (Idle past 1724 days)
Posts: 652
From: Puyallup, WA.
Joined: 02-04-2003


Message 61 of 200 (289863)
02-23-2006 5:27 PM
Reply to: Message 60 by arachnophilia
02-23-2006 4:16 PM


Question for Arach or anyone
Do modern reptiles have color vision?
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Mallon
Inactive Member


Message 62 of 200 (289902)
02-23-2006 8:43 PM
Reply to: Message 61 by DBlevins
02-23-2006 5:27 PM


Re: Question for Arach or anyone
Yes, most do, I believe.
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arachnophilia
Member
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 63 of 200 (289905)
02-23-2006 8:50 PM
Reply to: Message 61 by DBlevins
02-23-2006 5:27 PM


Re: Question for Arach or anyone
Do modern reptiles have color vision?

every place i've looked says that they do. the ranges and level of detail might be different.

however most modern reptiles aren't a good indicator for dinosaurs though. crocodiles are vaguely related: dinosaurs have a number of "crocodilian" thecodont features. dinosauria as a whole is kind of halfway between crocodiles and birds, and most paleontologists now consider them closer to birds -- being warm blooded, upright, bipedal animals (the quadrupeds all evolved from bipeds, so they bear their weigh over the hind legs, not spread out on all four like a croc) many of which were covered in feathers. recent studies suggest bird-like innards, too: pneumatized bones indicate complex air-sac systems connected to the lungs, so they weren't breathing with their ribs like crocs do.

dinosaurs are not true reptiles in any sense of the word. but if animals indicative of their ancestors, and the animals descended from dinosaurs both have color vision, dinos probably did too.


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werechicken
Inactive Member


Message 64 of 200 (295221)
03-14-2006 12:10 PM
Reply to: Message 63 by arachnophilia
02-23-2006 8:50 PM


Re: Question for Arach or anyone
let's not forget that all mammals evolved from reptiles and we, for the most part don't have great colour vision, most mammals have very good night-vision, which automatically rules out colour vision (we have specific cells in our eyes, on lot for colour vision, one lot for night vision) the primates evolved colour vision to detect ripened fruit, it is possible birds evolved good colour vision for similar reasons early in their ancestory
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arachnophilia
Member
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 65 of 200 (295352)
03-14-2006 8:28 PM
Reply to: Message 64 by werechicken
03-14-2006 12:10 PM


Re: Question for Arach or anyone
let's not forget that all mammals evolved from reptiles

close. the ancestors of mammals diverged from the "reptilian" line before proper reptiles appeared. but yes, we have reptilian ancestry.

reptiles do apparently have good color vision.


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extremophile
Member (Idle past 3543 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
http://www.palaeos.com/Vertebrates/Units/350Aves/350.200.html

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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arachnophilia
Member
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 67 of 200 (302768)
04-09-2006 11:30 PM
Reply to: Message 66 by extremophile
04-09-2006 9:24 PM


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.

well, this was sort of my thought, minus the long-disabled. i think that dinosaurs had feathers for about as long as they've been dinosaurs. however, as others have pointed out in this thread, longisquama's "feathers" are quite questionable. i have not been able to find any more decent information, and no consensus. either way, though, i think it indicates a trend toward heat-regulation, with animals like dimetrodon included. with good heat regulation comes upright posture (dinosaurs) and skin-coverings (feathers).

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?

not exactly. dromeosaurs are clearly less capable of flight than archie was. one needs only look at the heavier build and shorter arms. but the argument for a dromeosaurid archaeopteryx is a good one -- it's just that all the dromeosaurs we have come AFTER archie.

i highly suspect that velociraptor and his kin had fully formed flight feathers, and wings analagous to archie's. it's just a guess on my part, but we are finding more and more raptors that do. studies have shown that raptors must have been precision hunters: we know they basically went for the jugular -- some mild flight ability would probably help that.

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?

well, there's basically no way that archaeopteryx could fly, the way we think of flight. he might have been capable of gliding, or getting off the ground here and there, but he wouldn't have been a strong flapper.

i don't think he "devo"-ed from a flying bird. there are too many similarities with ground based dinosaurs. it would be a remarkable case of convergent evolution -- what evolves to look exactly like their distant ancestor? i do suspect there was some wobble back and forth developing flight capabilities, but he's definitally a dinosaur, descended from dinosaurs.

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.

i don't know a lot about sauropods, but it's important to remember that they evolved from bipedal dinosaurs. if they were in fact cold-blooded, it's because their metabolism slowed to accomodate their size, and they evolved from warm blooded animals.

it's also important to note that this would make them the only upright-standing cold blooded animals in the history of the earth.

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.

well, we think of "warm blooded" and "cold blooded" as the only options. there are multiple steps in between the two extremes. it's not like they just switched over one day. but dinosaurian physiology is quite different than cold blooded reptiles.

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;

yes. this was discovered some time after my first post in this thread. i added it in an additional post.

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.

i think that's a little older. but yes, he is VERY dromeosaurid. also, they recently discovered that the hip was not turned back as far as previously thought -- on par with the reversal seen in dromeosaurs.

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.

i'm not sure. it's good to remember that most dromeosaurs were pretty small. we're used to thinking of velociraptor as we saw him in jurassic park. really, he wasn't much bigger than the average household dog. there are good arguments that make him a runner, though. there's a lot of debate about archie, but i suspect he will be seen as a runner too, as every other dromeosaurid was.


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extremophile
Member (Idle past 3543 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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arachnophilia
Member
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 69 of 200 (303066)
04-10-2006 9:26 PM
Reply to: Message 68 by extremophile
04-10-2006 1:50 PM


Re: 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?

well, the genetic situation is that all birds have a gene for foot-feathers. there is another gene that modifies the foot-feather gene, and turns the feathers into scuts. turning that gene off results in foot-feathers. the scute gene one its own does nothing, it needs the feather gene to modify.

so that basically proves that feathers had to come first, and bird-scutes evolved from them. HOWEVER. it's entirely possibly that this is an evo-devo thing. it might be that feathers, in turn, came from scutes, and modification just brings a recessive trait out. however, considering what he know about earlier dinosaurs and feather, this does not appear to be the origin of feathers at all. feathers seem to have come from hair-like insulating adaptations, not plate-like "scales."


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extremophile
Member (Idle past 3543 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
http://news.bbc.co.uk/2/hi/science/nature/3762626.stm

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
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arachnophilia
Member
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 71 of 200 (304027)
04-13-2006 5:34 PM
Reply to: Message 70 by extremophile
04-13-2006 3:40 PM


Re: feathers, scutes, etc
The earliest known fossil of bird embryo, had fully formed feathers, whereas most of the arboreal birds today born featherless

lots of other birds aren't, though. from the article:

quote:
Prococial birds - like chickens, ducks and ostriches - produce young which are immediately competent: they have downy feathers, can run about and feed themselves almost as soon as they hatch.

it also seems to be a very mature embryo, with fully formed bones:

quote:
"All its bones are formed and its feathers are very well developed."

This maturity means the bird must have been "prococial".


which is kind of interesting. i'll try to track down a real picture the fossil (i'm starting to dislike artist interpretations). but it appears that the digits are fused -- one of the primary factors i'd look for in calling something a bird. it also seems to have a beak? but it still has a tail, which is even stranger. it was contemporary to confuciusornis, which lacked a long tail, but also lacked fused digits.

curious -- these adaptions seem not have evolved sequentially.

[AbE]also, i think the interesting there is that this might be further indication, recapitulation-wise, that feathers were developed first, and featherlessness was a subsequent adaptation.[/AbE]

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.

that was poorly worded in the article, wasn't it?

here's the reference: http://www.nature.com/nature/journal/v438/n7066/abs/nature04356.html

unfortunately, i can't get the whole article, but the abstract sure doesn't say either.

This message has been edited by arachnophilia, 04-13-2006 05:35 PM


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CACTUSJACKmankin
Member (Idle past 4222 days)
Posts: 48
Joined: 04-22-2006


Message 72 of 200 (305940)
04-22-2006 1:52 PM
Reply to: Message 1 by Nuggin
10-04-2005 12:26 AM


quote:
you evos assert birds descended from dinosaurs. This is counter-intuitive: very large animals (dinosaurs) evolving into predominantly small animals (birds) = nonsense.

Aside from the fact that that statement demonstrates a profound ignorance of evolution, the point that he is making is wrong. Archaeopteryx is within the dromeosaurid group of dinosaurs, which is the group that contains deinonychus and velociraptor. The dinosaurs from this group weren't the size of T-Rex, velociraptor was 3 feet tall.

A recent fossil found that archaeopteryx had a hyperextended second toe (velociraptor's sickle toe). It obviously wasn't as pronounced as in velociraptor or it would have been noticed before. This is significant because dromeosaurids are the only group of animals with hyperextended second toes, thus archaeopteryx is clearly a dinosaur. Yet archaeopteryx has feathers and a wishbone and a brain that was suitable for flight (based on CT scans of the skull), thus it is clearly a bird. If this animal is not a convincing missing link, then there is no such thing as a missing link, there is no fossil we would ever find that would convince you, and congratulations you are a stubborn creationist whose position bares no relation with the facts.


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arachnophilia
Member
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 73 of 200 (306034)
04-22-2006 10:53 PM
Reply to: Message 72 by CACTUSJACKmankin
04-22-2006 1:52 PM


This is significant because dromeosaurids are the only group of animals with hyperextended second toes, thus archaeopteryx is clearly a dinosaur dromaeosaur.

fixed. archaeopteryx is not only most certainly a dinosaur, but he is also a dromaeosaur. it's not just the second toe that gives this away -- his anatomy is very, very similar to other dromaeosaurs. they all have very long arms and semi-lunate carpals, and wishbones, for instance.

Yet archaeopteryx has feathers and a wishbone and a brain that was suitable for flight (based on CT scans of the skull), thus it is clearly a bird.

why? dinosaurs had feathers, and fused clavicles (wishbones) are being found more and more in dinosaurs that obviously could not fly. allosaurus has one.

If this animal is not a convincing missing link, then there is no such thing as a missing link, there is no fossil we would ever find that would convince you, and congratulations you are a stubborn creationist whose position bares no relation with the facts.

haha well said. there are things that make archaeopteryx special, yes. his brain (like you mentioned) and the proportion of his arms are flight-adaptaive features that other dromaeosaurs don't have (iirc about the brain). but most of the other avian features are shared by other dromaeosaurs (and even some less avian dinosaurs). i really don't see archaeopteryx as all that special, in light of the huge trend towards avian features in maniraptorian theropods during the late jurassic/early cretaceous. he's just a feathered dinosaur, in my mind.


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CACTUSJACKmankin
Member (Idle past 4222 days)
Posts: 48
Joined: 04-22-2006


Message 74 of 200 (306093)
04-23-2006 10:40 AM
Reply to: Message 73 by arachnophilia
04-22-2006 10:53 PM


This illustrates what makes me crazy about creationists. See, this is a legitimate discussion of what makes an feathered dinosaur a bird transition or not and where archaeopteryx fits into all of this. My problem with creationists is that they don't do this, they dismiss these fossils. They dismiss it as just a bird, just a dinosaur, or, most egregiously, a fake. They don't look at the fossil evidence as we do when we discuss it.
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arachnophilia
Member
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 75 of 200 (307780)
04-29-2006 3:48 PM
Reply to: Message 74 by CACTUSJACKmankin
04-23-2006 10:40 AM


See, this is a legitimate discussion of what makes an feathered dinosaur a bird transition or not and where archaeopteryx fits into all of this.

don't get me wrong, archaeopteryx IS transitional. all dinosaurs are, but archie is a darned well preserved example of the tendency towards avian features. i just don't think he's THE missing link between birds and dinosaurs, just a relatively common featherd dinosaurs with a few more avian features than most.

My problem with creationists is that they don't do this, they dismiss these fossils. They dismiss it as just a bird, just a dinosaur, or, most egregiously, a fake. They don't look at the fossil evidence as we do when we discuss it.

yes, that really is the problem. they draw lines in the sand, and then have to struggle to fit everything either on one side or the other so they can affirm their pre-concieved ideology. once it fits, it doesn't need to be dealt with anymore.


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