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Author Topic:   Archaeopteryx and Dino-Bird Evolution
arachnophilia
Member (Idle past 1343 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 44 of 200 (288963)
02-21-2006 1:28 AM
Reply to: Message 43 by Mallon
02-17-2006 8:49 AM


more on longisquama
I completely agree. But I don't know of anyone who is refering to some theropods as flightless birds without good reason. Note that I don't necessarily subscribe to this idea; just playing devil's advocate.
i picture dinosauria as a whole precariously perched between the ancient ancestors of crocodiles and modern birds. even the most un-bird-like dinosaurs share many birdlike features: upright posture, hips, hollowed bones, probably warm blood, etc. it's romantic to think of velociraptor like a big bird -- and it's a good comparison. it would be very much like flightless predatory bird. i'm willing to bet that it even had wings (in terms of feathers).
but it's not a bird. and it's not a crocodile. it's somewhere in the middle.
Very well. That's still very much a subjective choice, as I'm sure you will agree. Other scientists might chose another apomorphy by which to identify birds. Still others would rather describe birds based on their relationships to other groups (i.e. stem- or node-based definitions).
yes, it's quite a tough question of where we draw the line. what is a bird? what's a dinosaur?
i'm currently giving two books a read. i picked up "the dinosaur heresies" by bakker, and "predatory dinosaurs of the world" by gregory paul at the used bookstore today. as it stands, i think i will still contend that birds and dromeosaurids share a common ancestor, but are not closely related enough to put in the same clasification as "birds." the dromeosaurid line did not produce modern birds, if memory serves.
edit: it appears dr. bakker actually wrote something on longisquama. i'll see if i can find that paper, too:
quote:
Also Bakker (1975: p. 68) stated that the scales of Longisquama constituted a structural stage in the evolution of feathers.
Bakker, R.T. 1975. Dinosaur renaissance. Scientific American 232, 58-78.
http://app.pan.pl/longisquama.htm
it'd be great to have his input here, though since he only posted once, i doubt he'll be back. i'm frankly just amazed that even posted here at all.../edit
There has certain been much literature on the issue. For the pros, see:
Jones, T.D., J.A. Ruben, L.D. Martin, E.N. Kurochkin, A. Feduccia, P.F.A. Maderson, W.J. Hillenius, N.R. Geist, and V. Alifanov. 2000.
Nonavian feathers in a Late Triassic archosaur. Science 288: 2202-5.
from what i've heard, feduccia's theories are not well regarded in the paleontology community. i've heard some even claim that he is intellectually dishonest, or that he is ignorant of dinosaurian biology and anatomy.
he alleges that birds evolved from other thecodonts, not theropod dinosaurs, and that the dromeosaurid likeness is just convergant evolution. that's a little bit extreme -- i doubt they are that distantly related, though i do think he may have a point about bird-like tendencies evolving fairly early. there is even the odd bird-like feature in crocodiles, but not enough to establish any close relationship. the similarities are veen more present in dinosaurs, and most present in theropods like dromeosaurs.
The cons:
R.R. Reisz, H.-D. Sues. The "feathers" of Longisquama. Nature 408:428.
unfortunately, i can't get the article at just this second -- i'll have to take a trip to library, unless you can post some pertinant quotes. i'm kind of interested in what people more knowledgeable than i are actually saying about this "feathered" lizard.
As far as I'm concerned, even if the 'feathers' of Longisquama and birds were one and the same (which I don't think they are), the rest of the skeleton just doesn't compare at all between the two.
no, it doesn't at all, does it? actually, it's skeleton (the parts we have) are fairly confusing as it is:
it's hard to tell from the illustrations what's really going on -- i'm not very qualified to make any kind of good scholarly opinion here -- but it appears to have clavicles, long (mobile?) shoulder blades, and the start of some kind of breastbone. now, chameleons have similar shoulder blades, and i think breast-bones. but it's clavicles aren't very lizard-like.
Jaime Headden reconstructs longisquama like a theropod:

This website is frozen.
which, imo, is probably very wrong. it doesn't really look like a dinosaur to me. actually, it looks more like a pterosaur. it's not, but it has some similarities. the hand/wrist structure in particular, and the skull. dinodata says:
quote:
In Peters, D., 2000. "A reexamination of four prolacertiforms with implications for pterosaur systematics," Rivista Italiana di Paleontologia e Stratigrafia 106(3): 293-336 [December 2000] the describer supersedes all previous work on Longisquama, Cosesaurus, and Sharovipteryx and places them well inside the Prolacertiformes. In particular, this removes Longisquama from Dinosauria.
Longisquama insignis known primarily from a crushed fossil preserving only the fore parts of the animal, and also a number of disassociated "long scales." was found in 1969 in Kyrgyzstan by the Russian insect paleontologist A.G. Sharov. The skull appears to have diapsid openings.
Dinodata.net - Refinansiering av gjeld og ln
in short, i don't really know what it is. but it's not a dinosaur, which means it's not a theropod, which means it's not a bird. it seems to be a member of archosauromorpha, but not an archosaur.
Longisquama definitely isn't a contender, at least as far as bird ancestry is concerned (which I know isn't what you're contending, arachnophilia).
no, absolutely not. i was using it as an indication that (if those ARE feathers then) some of the particular peculiar features we assign to dinosaurs and birds may not be so new, and that feathers may actually have existed prior to dinosaurs in some primitive form. if i recall, feduccia contends that longisquama and some other ridiculous lizard are the "true" ancestors of birds. which, i think, is laughable at best.
This message has been edited by arachnophilia, 02-21-2006 01:36 AM
This message has been edited by AdminJar, 02-21-2006 10:48 AM


This message is a reply to:
 Message 43 by Mallon, posted 02-17-2006 8:49 AM Mallon has replied

Replies to this message:
 Message 45 by Mallon, posted 02-21-2006 11:34 AM arachnophilia has replied

  
arachnophilia
Member (Idle past 1343 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 46 of 200 (289334)
02-21-2006 6:52 PM
Reply to: Message 45 by Mallon
02-21-2006 11:34 AM


drepanosaurs? is feduccia nuts?
You're right in saying the dromaeosaurid line did not produce birds. It is commonly argued that the deinonychosaurs (dromaeosaurids + troodontids) are the sister taxon to the birds.
my opinion is that either the ancestor of dromeosaurs, or a very early dromeosaur spun off into birds, but that the dromeosaurs we commonly associate with the group (velociraptor, deinonychus, and maybe even archie) are from the "dinosaur" line, not the "bird" line.
But maybe after reading Paul's book, you will change your mind. That book is terribly out of date, mind you. I'm just impressed that you were able to pick up PDW at a used book store -- that thing is very hard to come by.
i was suprised, too. the amount of actual data and reconstructions in it is just incredible. i imagine it probably is a bit out of date -- it was written in 1988. but it does seem to be of quite modern thought, at least. there's lots of depictions and reconstructions that show running, warm blooded, and feathered dinosaurs.
obviously, it couldn't have incorporated the very recent discovery that tyrannosaurids had feathers. but that's science: always changing and updating itself. amazingly, it was MORE up-to-date than another newer book i looked at, and a fraction of the price.
Is it any wonder creationists continually cite him for support?
...well, actually, it kind of. granted, they cite ANYONE who disagrees with mainstream evolutionary theory, but in the process they tend to prop up people who still obviously understand something about evolution. feduccia is NOT saying that birds were created, or didn't evolve. he's saying they evolved from something besides theropod dinosaurs. it's just an excuse to write off archaeoptryx as "not a transitional species."
I think he has even changed his tune now and argues that neither birds NOR deinonychosaurs are theropods, but evolved instead from a drepanosaurid-like ancestor. There was a paper on this recently...
ok, that just makes my brain hurt. how are deinonychosaurs NOT theropods?
granted, drepanosaurids are another oddity. i mean, if someone looked at ONLY the skull and neck of one, they might see some similarity to birds, especially in megalancosaurus (the other "ridiculous" example i mentioned above). but the rest of the body is pretty typical lizard.
i mean, if i had to pick an ancestor for this guy:
would i go with:
or?
birds aside, the ancestry of deinonychosaurs is, um, blindingly obvious. his changing his tune to include deinonychosaurs (if true) is an obvious sign that EVEN feduccia recognizes the similarity between birds and dromeosaurs.
If memory serves me, the Reisz paper is available on his lab website for download.
ok, i'll look a little harder
edit: found it, i'll give it a read.
This message has been edited by AdminJar, 02-21-2006 05:55 PM
This message has been edited by arachnophilia, 02-21-2006 06:57 PM


This message is a reply to:
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arachnophilia
Member (Idle past 1343 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 48 of 200 (289341)
02-21-2006 7:12 PM
Reply to: Message 45 by Mallon
02-21-2006 11:34 AM


Re: more on longisquama
If memory serves me, the Reisz paper is available on his lab website for download.
that was a much shorter article than i expected. here's the important part of the article:
quote:
There are no feather-like features on the distal portion of the appendage. Here, two corrugated membrane-like surfaces touch along their leading and trailing edges to form wide, smooth bands. The two membranes were apparently supported by a median veinlike structure extending the length of the appendage. This has been proposed as the homologue of the rhachis of avian feathers2. On either side of this ”vein’, the external surfaces of the appendage are corrugated. This corrugation varies along the appendage: proximally, individual rugae are relatively large and widely spaced, but in the distal portion they are smaller and densely packed. The densely arranged distal corrugations have been compared to the pinnae of avian feathers2, but the fossils indicate that these are formed on a membrane-like structure on either side of the ”vein’.
The fossils were split into part and counterpart during collecting, and most of the appendages are now preserved as impressions of their left and right sides, without the intervening sediment core. The surfaces of both the part and counterpart impressions of individual appendages are concave, an indication that these structures are three-dimensional. In contrast, the parts and counterparts of feather impressions in Archaeopteryx are concave and convex, respectively.
We believe that the dorsal appendages of Longisquama are highly modified scales, as suggested previously1,3, rather than feathers.
Examination of the holotype of L. insignis (PIN 2584/4) suggests that they were anchored in the skin or epaxial muscles.
1. Sharov, A. G. Paleontol. Zhur. 1970, 127-130 (1970).
2. Jones, T. et al. Science 288, 2202-2205 (2000).
3. Feduccia, A. The Origin and Evolution of Birds (Yale Univ. Press,
New Haven, 1996).
http://www.utm.utoronto.ca/~w3reisz/pdf/Longis.pdf
he seems to say that feduccia says they are highly modified scales, not feathers. maybe i should track down feduccia's paper too...


This message is a reply to:
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arachnophilia
Member (Idle past 1343 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 52 of 200 (289350)
02-21-2006 7:47 PM
Reply to: Message 51 by jar
02-21-2006 7:43 PM


both of you go away
jar, it was quite a waste of space for a post (even four months ago). no real argument. you'll noticed i posted a very lengthy and detailed refutation of his points. a post of "crap!" doesn't do much for the argument, either way.
and we've got some interesting bird evolution discussion going here right now. you know where to take administration complaints.
This message has been edited by arachnophilia, 02-21-2006 07:47 PM


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arachnophilia
Member (Idle past 1343 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 54 of 200 (289640)
02-22-2006 9:07 PM
Reply to: Message 45 by Mallon
02-21-2006 11:34 AM


speaking of velociraptors
i was poking around your site, and i noticed some of that outdated information from the gregory paul book i'm reading show up:
quote:
V. mongoliensis (and deinonychosaurs in general) is most revered for its two sickle-shaped claws, each of which extended from the second toe of the hind foot. It could latch onto inauspicious prey with its grasping hands and use these talons to kick into the bellies of its victims, cutting deep lacerations into the animal's flank (Paul, 1988).
now, i don't mean to call you on this to be rude or anything -- this is a pretty persistent idea and probably still very debatable. but i'd like to make an argument, on topic to this thread, about possible deinonychosaur hunting methods.
a recent study showed that velociraptor claws would have been poor slicing blades. i think these were the same guys who did a similar study on the teeth of sabre-toothed cats. in both studies, they made the case that these similarly-shaped weapons were good at precision puncturing, not tearing or slicing. if we think about it for a second, it makes sense. nearly every other theropod hunted with its teeth, and used them to tear out a large gouge in the prey. they would probably circle and wait for the prey to die, like sharks do. their teeth are designed for slicing, like knives. but deinonychus does something different. it hunts with it's feet, as well as (maybe) its teeth.
two basic bits i think everyone agrees on. 1) that the claws were hunting weapons, not dominance-fighting weapons. too much risk in breaking such a large claw. 2) to use them, deinonychosaurs had to be airborn. now, if we compare a velociraptor skeleton to our friend archaeopteryx, we find lots of similarities. enough that most people now consider it a dromaeosaur. we also have the raptor named after paul, which is even more closely related. both have full flight-feathered, lift-generating wings. both (iirc) lacked the ability to fly.
the study above suggests that velociraptors used precision, and went for the jugular. this approach makes more sense over the brute-force "gut the victim" idea for such a small animal. the claws, aimed correctly, would deliver a fast, fatal, and low-contact wound to the prey. there is actually evidence supporting this idea, too. modern raptors hunt with their feet, in a similar, precise way. and the famous velociraptor/protoceratops fight scene:
quote:
One of the most complete skeletons of V. mongoliensis was found intertwined with the remains of Protoceratops andrewsi, an early horned dinosaur. The fossilized specimen, commonly referred to as the "fighting dinosaurs," reveals that the two contenders died in combat; the predator's hind foot embedded in the thorax of its victim, while having its own arm bitten in turn (Glut, 1997; Novacek, 1996). It is not known exactly why these animals were fighting, although recent evidence suggests that the victims died as a result of an intense rainstorm (Novacek, 2002).
the velociraptor has its claw hooked into the protoceratops' neck, as this picture shows.
i'd like to make an additional suggestion: that deinonychosaurs had lift-generating wings, which they would use to assist in jumping attacks, slow air-speed for precision kills, and intimidate/distract prey from biting important parts of their bodies. this is probably why the protoceratops has grabbed onto an arm: he got lucky and found a bone amid all the feathers. i would imagine that the wings were probably also brightly colored to draw the victims attention (presuming color vision in the prey, anyways). it would make for good maiting/rivalry displays, too.
anyways, think this is a reasonable idea? i'm not well versed enough in the area to know some of the specifics of arm anatomy and movement. what do you think? could raptors "flap?"
This message has been edited by arachnophilia, 02-22-2006 09:10 PM


This message is a reply to:
 Message 45 by Mallon, posted 02-21-2006 11:34 AM Mallon has replied

Replies to this message:
 Message 55 by MangyTiger, posted 02-22-2006 9:40 PM arachnophilia has replied
 Message 57 by Mallon, posted 02-23-2006 9:41 AM arachnophilia has replied

  
arachnophilia
Member (Idle past 1343 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 56 of 200 (289653)
02-22-2006 11:08 PM
Reply to: Message 55 by MangyTiger
02-22-2006 9:40 PM


the bbc and "walking with dinos"
A two part TV show (The Truth About Killer Dinosaurs) with one of the episodes based on this work was shown over here in August/September last year.
It was reasonably interesting but a bit dumbed down for my taste, like all recent BBC shows with any science content. The Beeb appears to have taken a policy decision not to produce science shows as such any more, rather it produces entertainment shows with a fairly minimal amount of science in them
there was one i saw recently, as a spin off from "walking with dinosaurs." it was all about one specific allosaurus fragilis specimen, and the life it led. it had considerably more science content than i was expecting. they showed the actual skeleton (gasp!) and examined the various evidences of wounds. they explained how they how old (from time of death) each was, too. in fact, they gave some half-decent science backing for nearly everything they said.
still quite dumbed-down of course. but a vast improvement over "walking with dinosaurs." i think it was an effort to say "we're not making this stuff up wholesale."
i dunno, it's like they think poking around in the sand and chiselling rock all day under the hot badlands sun isn't interesting or something.
This message has been edited by arachnophilia, 02-22-2006 11:10 PM


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arachnophilia
Member (Idle past 1343 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 58 of 200 (289845)
02-23-2006 3:52 PM
Reply to: Message 57 by Mallon
02-23-2006 9:41 AM


Re: speaking of velociraptors
Otherwise, I agree with everything you say. Except the bit out Velociraptor having brightly coloured feathers to get the prey's attention. If you're a predator, I think the last thing you want to do is to get your prey's attention (that's what made those WWD shows such a tragedy -- the big theropods would run up to their prey, roaring all the while and scaring them away).
yes, that's probably a good point.


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 Message 59 by jar, posted 02-23-2006 4:05 PM arachnophilia has replied

  
arachnophilia
Member (Idle past 1343 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 60 of 200 (289851)
02-23-2006 4:16 PM
Reply to: Message 59 by jar
02-23-2006 4:05 PM


Re: coloration
well, sexual dimorphism is also a possibility. males could be brightly colored and females dull, or vice versa. i was also thinking of bright spots on the wings that would be concealed in stalking mode...
but short of "it's not good hunting strategy" it's really all idle speculation.


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 Message 61 by DBlevins, posted 02-23-2006 5:27 PM arachnophilia has replied

  
arachnophilia
Member (Idle past 1343 days)
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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arachnophilia
Member (Idle past 1343 days)
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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arachnophilia
Member (Idle past 1343 days)
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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arachnophilia
Member (Idle past 1343 days)
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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arachnophilia
Member (Idle past 1343 days)
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: Could ‘four-winged’ dinosaurs fly? (Reply) | Nature
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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arachnophilia
Member (Idle past 1343 days)
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.


This message is a reply to:
 Message 72 by CACTUSJACKmankin, posted 04-22-2006 1:52 PM CACTUSJACKmankin has replied

Replies to this message:
 Message 74 by CACTUSJACKmankin, posted 04-23-2006 10:40 AM arachnophilia has replied

  
arachnophilia
Member (Idle past 1343 days)
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.


This message is a reply to:
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