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Author Topic:   Archaeopteryx and Dino-Bird Evolution
arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 3 of 200 (248761)
10-04-2005 2:04 AM
Reply to: Message 1 by Nuggin
10-04-2005 12:26 AM


i know this has been done before.
the problem (as we ran into with david in the chat the other night) is that creationists do not ALLOW evidence of transition. the first creationist post here will, of course, be to draw an arbitrary line in the sand.
this is a dino, this is a bird. and there's nothing in between. archaeopteryx? that's just a feathered dinosaur. not a transition. or wait, was that a toothed bird? i forget. it's particularly ironic because the creationist community can't agree on what it is, exactly. it can't be a transitional, because they don't exist, so it's gotta be "just" one or the other.
it's sort of circular, really. it amounts to "there aren't any because i've defined the system so they can't exist."
the problem, really, comes with the fact that we actually know a whole heck of a lot about how feathers and flight evolved. we have feathers at all kinds of stages of transition. and we have feathered dinosaurs with all kinds of combinations of theropodal and avian features. archaeopteryx is not a lone example of this.
in fact, we are finding more and more dinosaurs with feathers.
i suspect as this thread progresses a little, i'll make the point by posting a bit about a few of them. but one has to be up on paleontology to really appreciate and understand what's been going on.
just for kicks, here's the wikipedia category on feathered dinosaurs and rehistoric_birds]-->prehistoric birds. the line's a bit fuzzy, so there's some overlap.
This message has been edited by arachnophilia, 10-04-2005 04:13 AM

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arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 5 of 200 (248771)
10-04-2005 4:18 AM
Reply to: Message 4 by Nuggin
10-04-2005 3:06 AM


Re: Oh, I know
He proposed that Archie was good evidence for ID, since the fully formed feathers appeared suddenly in the fossil record, and that earlier forms wouldn't serve any purpose.
which, of course, is not true, as you pointed out:
I pointed out that they were predated by more primative feathers (downy feathers for example) which serve uses other than flight. Warmth for example.
even if they don't supply warmth, they also can serve a DISPLAY function.
His quote after that - "I've never heard of such things, but if they did exist, that would be a good step toward me accepting evolution."
Excellent, I thought. Finally, evidence trumps ignorace.
I posted links to pictures and definitions, explainations, evidence. The whole boat.
The response "Well, those websites say that the fossils show "downy like" feathers, not downy feathers. How do we know they have downy feathers and not just hairs that look-like downy feathers."
that's just silly. they say "downy-like" because it's NOT down, just remarkably like it. down is technically the undercoat of a bird's feathers, attached to larger more developed feathers. the "down" on these dinosaurs is exactly the same as the down a baby bird would grow -- they just never grow the major feathers.
it's sort of like calling an axelotl "salamander-like." technically, the only reason it's not a salamander is because it never goes through the metamorphosis to become one. it stays in the "baby" form its entire life.
it's basically the same thing.

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arachnophilia
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Posts: 9069
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Message 7 of 200 (248777)
10-04-2005 4:42 AM
Reply to: Message 6 by Thor
10-04-2005 4:23 AM


That is, clear that the particular poster has a rather poor understanding of evolution.
i think that's actually the primary cause of the problem here. people don't understand it, haven't had enough actual exposure to the science, data, and evidence, and just basically aren't familiar with the intricacies of what a skilled person can tell from the evidence.
david, for instance, didn't know how we could tell that some dinosaurs had feathers -- something very obvious if you've ever seen a picture of the archie fossils (see above). but that's the kind of thing the average spectator can tell, so we could tell that david had never seen archaeopteryx (so we showed him). the trained professional can tell much, much more. for instance, how the muscles attached to the bones. how it moved. what the animal ate. and sometimes something about the social structure of the animal, based on the context it's found in.
it's almost like the creationists actually think the scientists look at something in isolation for three seconds, and then make up a fairytale to explain it. the don't seem to realize that people who spend their entire lives studying a field in minute and technical detail probably know a lot more about it than they do.

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arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 10 of 200 (249257)
10-05-2005 8:31 PM


ok, this is annoying me.
if anyone saw this thread with the mp3's of jared hoag and kent hovind on the radio, hovind keeps making this one particular claim, and i'll paraphrase.
evolutionists say that birds evolved from therpods, saurischian (lizard hipped) dinosaurs, not ornithischian (bird hipped) dinosaurs. on the surface, that's a pretty convincing argument. bird ≠ bird? what sense does that make.
pretty good sense, actually, when you realize that names don't mean a whole heck of a lot, especially coming from early paleontologists. why, if we just looked at names, we might conclude that basilosaurus was a reptile -- when in fact it was a mammal.
it turns out that modern birds have -- get this -- lizard hips. they lack the forward-pointing portion of the pubis found on ornithischian dinosaurs. even more interesting is that archaeopteryx, as expected, has a transitional hip structure. the pubis points very slightly backwards, but not at an angle sharp enough to be considered modern. it's literally very slightly past half-way between the two angles. curious, hmm? other theropods, like the dromeosaurids (velociraptors) have pubic bones that point nearly straight down.
i'm gonna look and see if i can find some skeletons of other feathered dinos and prehistoric birds and see if i can put a few more dots on the "connect the dots" argument here. but here's a really good start: Dinosauria On-Line
but here's something i didn't know: (from the above source)
quote:
In modern bird embryos the pubis initially points forward as in "lizard-hips," then rotates backwards as the embryo develops.2

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arachnophilia
Member (Idle past 1452 days)
Posts: 9069
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Message 21 of 200 (250639)
10-11-2005 4:04 AM
Reply to: Message 14 by Springer
10-10-2005 9:01 PM


archaeopteryx is VERY transitional
In its most important feature, namely flight feathers, archaeopteryx is no less of a bird than modern birds.
in its feathers, yes.
If it were alive today, it would be classified as a bird.
this is not true, and obvious to just about everyone, including its early creationist detractors. they argued that archaeopteryx was a forgery -- comprised of the skeleton of a compsagnathus with faked feather impressions. why? because if we take away the feathers for a second, archaeopteryx only looks remotely like a bird, but much more like a small theropod:
here's a chicken for comparison:
its skeleton has far too many features in common with small theropod dinosaurs for it to be a true bird, in the modern sense. let's look at a few of them, shall we?
archaeopteryx not only has teeth, but lacks a bill. there is no hard covering on the end of its snout. it has a skull much like that of a theropod. it also has a long tail, which has not fused into a bird's pygostyle. this indicates that it probably had a level posture like most theropod dinosaurs, not the more upright posture of modern birds -- it wouldn't balance or walk like a bird.
the complete lack of anything like a pygostyle is kind of interesting, actually. several small theropod dinosaurs, the dromeosaurids, have the tips of their tails fused by long extensions of the vertebral bones. archaeopteryx is curiously LESS avian than say velociraptor in this respect.
But there is no evidence that it wasn't as powerful a flyer as a modern bird.
considering that archaeopteryx has a tiny sternum, and lacks the predominant breastbone and keel of modern birds, it would have been flat-out incapable of powered flight -- at all. it has no bone with which to attach the enormous flight muscles required to generate lift. it could flap its arms, but so could dienonychus. neither would have gotten off the ground with it, even with feathers. this isn't dumbo, and feathers are not magic.
heck, even the chicken above would be more capable of powered flight than archaeopteryx, and we all know chickens don't fly for any substantial length of time.
By the way, three living birds today have claws on their wings and are still considered true birds.
let's make no bones about this, because this is a major difference. archaeopteryx does not have a true wing. it's claws are on a HAND, not a wing. in modern birds, the wing bones are thick, formed of fused digits 2 and 3. archaeopteryx has 3 individual slender digits. in its legs, it has a full fibula, extending all the way to ankle, and has a fifth toe. modern birds do not have a fifth toe, and their fibulas stop about halfway down the tibia. theropod dinosaurs, however, have all five toe and a full fibula.
archaeopteryx is, in almost every respect, a small theropod dinosaurs. so what makes it a BIRD, exactly? feathers, obviously. aside for that, it has very avian hips (as do the dromeosaurids), the half-crescent wrist bones (as do the dromeosaurids), a wishbone (fused clavicles), hollow bones, an opposed hallux (1st toe), and arms that are at least the length of its legs.
basically, calling a bird isn't exactly right. it's a theropod dinosaur in nearly every respect, with a few very key bird features that are really only seen upon close examination. it is quite a genuine mix, but if i were classify it as one or the other, it would definitally still be a dinosaur.
If archaeopteryx is the best evolutionists can come up with for transitional forms, their argument is weak indeed.
considering that archaeopteryx is exactly what we would expect to find to fid for a theropod-bird transition, and the fact that that transition is ALREADY strongly backed by numerous other dinosaurs, feathered or not, i would say the argument is very strong.
it would be very strong even without archaeopteryx or any other feathered dinosaurs. ornithologists have knows for 100 years or more that birds came from archosaurs, though not through dinosaurs. they were able to identify various archosaur features in birds. when the first dinosaurs skeletons were found, it was believed that birds came from the various "bird-hipped" dinosaurs, such as the ceratopsians (which, btw DO have beaks and quite bird-like hips). and when dienonychus was found, with its bird wrist bones, bird-like feet, fused tail vertebrae, long arms, and backward-turned "lizard hip" that nearly matches todays today's birds, well, the case pretty much closed.
The problem with evolutionists is that they minimize the need for transitional species, when the ToE demands literally millions of them in the past.
i should scan some of these diagrams from the book i'm currently perusing on the subject. one, for instance, shows the hip bones of the major families of dinosaurs throughout the entire mesozoic era. the progression of the saurischian pubis steadily backwards until you reach dienonychus and archaeopteryx is kind of startling. every group they mention, sauropods to ceratosaurs to allosaurs, to tyrannosaurs and ornithomimosaurs, to dromeosaurs -- they're ALL transitional. and when you stick a modern bird's hip on the end of the diagram, you have to spend a few minutes looking for the differences between it and the dromeosaurs. one wonders why they even bothered putting it on, it's barely any different.
no, we're not minimizing the need for transitionals. some of us have seen enough of these specimens to notice the transitions in just about everything, even if some are dead-ends.
My suggestion is to stop fixating on one or two questionable examples and look at what the present and the past show... that nature is fundamentally discontinuous.
we're not fixating on one or two examples. there are over a dozen feathered dinosaurs we've found, and they butt up and cross into early birds pretty well. the late cretacious theropods show lots of avian features across the board.
we talk about archaeopteryx because it's an example everyone's heard about, and generally considered the clincher to the debate. it's the particular example the creationists are asking for, but still reject upon seeing. it's clearly part bird, part dinosaur, maybe 40/60. we also talk about because it's not SUBTLE in it's transitional nature. it doesn't look like one or the other.
now, if you wanna discuss this little guy, be my guest:
sinornis has a pygostyle, and its metatarsels are partially fused. please note, PARTIALLY fused, as in not fully one or the other. it has the sternum of a bird, but not the keel. it's 2 and 3 digits in the hand are fused into a modern wing, but it has a theropodal-style head with teeth and lacks a bill. overall, it looks like a bird, not a dinosaur. it's differences are a little more subtle. if we saw one flying around today, no doubt we'd think it was a bird, not a dinosaur, until we saw its head.
but until the creationists get the bluntly obvious down about archaeopteryx, there's little point discussing the finer details of the ones a little further along the transition.
There are enormous differences between birds and reptiles, and it would have required at least tens of thousands of functional transitional forms to bridge the gap. You suppose that they existed but you have no proof and you can't even construct hypothetical intermediate forms.
wanna try this one again? as i've spelled out above, we have nearly every major feature of modern birds figured out in terms of origin. we know how each and every "hypothetical" step of feather development came about. i use quotes because we have an example of a feathered dinosaur species representing nearly every single one of them. we know how flight evolved, as an extension of the maniraptorian grasping action, and have the crescent wrist bones of velociraptor to prove it.
the supposed lack of intermediate forms exists only within the creationist's head. they refuse to see the blindly obvious -- that a theropod with a few bird features and feathers is transitional. how are we to expect them to see the more subtle commonalities between other forms?
I've noticed a conspicuous lack of illustrations in the literature of transitional species of, for example, between reptiles and birds,
you're not looking the right place. i checked out three encyclopedia-volume-sized books on this tonight. i rejected a fourth, larger one, which was totally about mesozoic birds because i was looking for illustrations of reconstructions -- not photos of the individual bones from various views.
i might note that these were pop-sci books. i didn't even bother going to the technical journals on the matter.
This is because evolutionists prefer to speak in very vague terms, glossing over critical details.
does what i wrote above sound like i'm glossing over details? i'll scan some illustrations if you'd really like. it's the creationists that can't seem fathom the vague and the obvious -- so why should we go into the technical?
They know perfectly well that any attempt to actually visualize a functional transitional forms that would preferentially survive by natural selection would be so laughable that all credibility in ToE would plummit.
yet there are two of them, right above. want some more? i'll post some more. creationists have this wonderful notion that transitionals don't exist because they can't be functional. what good is half a wing, right?
ask archaeopteryx. he has half a wing: feathers, but not wing bones. what did he use it for? was it an aid in running? did he glide from trees? these are sort of like flying, aren't they? good half-way points. maybe they were sexually selected for. what use does a peacock's tail have? certainly, it's not functional in any respect.
i think you fill find that if you go to a university library and check out a few good solid books on the matter you find volumes full of functional transitional forms, many of whom survive for a very long time.
edited image size to fix page width- The Queen
This message has been edited by arachnophilia, 10-11-2005 07:40 PM

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arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 22 of 200 (251467)
10-13-2005 2:03 PM


metatron -- read this post
i read your pnt, but we've currently got three dino-bird threads going on. one about the respiratory system, one about archaeopteryx as an example of the transition, and one about a new raptor reported today. i think this would be a good place to discuss tails, since archaeopteryx has one.
there's one simple problem with argument: all theropods are carnivorous, and the ones birds came from are probably all predatory, too. animals like the new raptor found today are basically well oiled killing machines.
and they're designed for speed, speed, and speed. simple dinosaur biology holds that the tail is used as counterbalance to the body, so the dinosaur can walk upright easily (or hold its head up, in the case of sauropods). they probably were used to help steer at high speeds, yes. and feathers would have certainly helped. but i don't think they evolved to run AWAY from something, even if they would have helped in extenuating circumstances. but the argument for flight feathers as extension of rudder-like tail feathers is a good one.

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arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 25 of 200 (251473)
10-13-2005 2:17 PM
Reply to: Message 24 by Chiroptera
10-13-2005 2:12 PM


Re: metatron -- read this post
that's a good idea, thanks

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arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 26 of 200 (251491)
10-13-2005 3:21 PM
Reply to: Message 23 by Chiroptera
10-13-2005 2:10 PM


avialae, but not aves
Archaeopteryx is a bird only because scientists have decided that they will make the definition of Aves broad enough to include Archaeopteryx. The boundaries of the classifications are artificial, and in this case they are arbitrarily placed so as to include Archaeopteryx.
i guess you called me on one so i get to call you one. the books i have place archaeopteryx in avialae, but not aves. it has something like this:
  • maniraptora
    • dromeosauridae
    • avialae
      • archaeopteryx
      • ornithurae
        • mononykus
        • ornithothoraces
          • enantionithes
          • carinatae
            • hesperonoris
            • ichthyornis
            • aves (modern birds)
              • paleognathae
              • neognathae
This message has been edited by arachnophilia, 10-13-2005 03:29 PM

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arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 28 of 200 (251499)
10-13-2005 3:56 PM
Reply to: Message 27 by Chiroptera
10-13-2005 3:38 PM


Re: Doh!
Heh. I have seen that classification scheme, too, so perhaps I shouldn't have been so quick with my fancy scientific terminology
it happens. god knows i just did it too, right?
This does sort of support our points, though (notice me making lemonade?): if one arbitrarily only considers Aves to be birds, then Archaeopteryx is then not a bird. If, on the other hand, all the members of Avilae have the features that we naturally want to associate with birds, then Archaeopteryx can be considered a bird.
the bird/dinosaur line is kind of fuzzy. technically, all birds are theropod dinosaurs -- but technically we're also reptiles, right? there is a distinct set of features that makes a bird a bird, just like there's a distinct set of features that makes a mammal a mammal. but in the transition areas, we would expect those to be fuzzy. some features would be present, some would not:
What is and is not a bird is rather arbitrary (like most definitions), and unfortunately for Springer's point, how one classifies Archaeopteryx is less important than the fact that it's classification brings up these issues, just as we would expect from a bird/theropod transitional.
and this is exactly what we see in archaeopteryx. it's not a bird, in my opinion, because it fails to possess a significant portion of those specific features. i would call it a feathered, avian dinosaur. but not a bird.
(By the way, I think it is a matter of contention among those who like to be involved in contentions whether Aves should be the crown group of modern birds or the crown group of modern birds and Archie. Since I'm not a biologist or palaeontologist, I don't have a dog in that race.)
yes, i notice that cladogram is different than mine. it's puts aves much higher, which i don't really agree with. that one does place archaeopteryx into aves. it's not so much that i have a dog in the race, i just think it makes a lot more sense the other way.
ah well, it's all arbitrary anyways, right? shall we debate this minor technicality?

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arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 30 of 200 (251507)
10-13-2005 4:25 PM
Reply to: Message 29 by Chiroptera
10-13-2005 4:13 PM


Re: Doh!
I was writing from the stand point of traditional taxonomy, which recognizes paraphyletic groupings. Not all biologists, or even all systemists, have yet adopted an entirely phylogenic approach to classification, so I will switch from one to the other as it is convenient for me. Bad habit on my part: it does open the possibility of equivocation.
i'm strictly practical, never having a good formalized biology or paleontology education, just a minor interest. so i look at specific features, especially in the hard fossilized parts.
which is why i don't consider archaeopteryx a bird -- it simply doesn't have the skeleton of one. which is the position i described above.
As far as whether mammals are descended from reptiles (or are reptiles or whatever) -- as I mentioned, I don't like that. I've read that the last common ancestor of modern reptiles and mammals was early enough that it still had many amphibian characteristics.
well, yes. birds still have a few reptilian characteristics, and modern reptiles still have some amphibian characteristics. if you look at skeletons only, the all have remarkably similar components.
I would assume, then, that as the line that led to reptiles further evolved their distinctive reptilian features, the synapsids would have evolved in a different direction (unless there was some sort of convergent evolution). Of course, on can define (and people did and probably still do) define reptile in such a way to include synapsids and therapsids. Me, I prefer to think of reptiles and mammals as closely related but independent lineages of the early tetrapod line. But, not being a biologist, there's no reason for anyone else to accept my musings
no, it sounds pretty accurate. we're just quibling over what to call a reptile. it's all the same, really.

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arachnophilia
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Posts: 9069
From: god's waiting room
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Message 31 of 200 (252933)
10-19-2005 1:08 AM


bump: still not a bird.
google, it turns out, is totally useless. anyways, i was searching for something else dinosaur related (sauropods) today, and stumbled across this page:
Lecture 19 - Late Jurassic: Solnhofen
now, i've been looking at similar pictures in books for my art project, but it's hard to find such clear diagrams on the web. take a look at the archaeopteryx compared to the pigeon (like i did above) and it compared again to dienonychus below. then look at the transitional chart of hands.

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arachnophilia
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Message 34 of 200 (279769)
01-17-2006 9:45 PM
Reply to: Message 33 by umliak
01-17-2006 12:58 PM


t. rex
t. rex's arms were so tiny because it didn't use them. i think of tyrannosaurids as land-sharks: a walking set of jaws. like most sharks, t. rex would probably have eaten whatever it could. its jaws are built for bone-crunching, and its legs are proportioned more and more for endurance walking towards the end of its reign. this indicates, for most, that rex was not a picky eater nor did he survive primarily by actively taking down prey. he would probably get to the prey last, and crunch through the bones to get the bits the smaller and faster hunters could not. arms are more or less useless for this purpose.
compare to a velociraptor, who has extremely long grasping arms useful from hunting, and legs proportioned for sprinting.
t. rex is not by any means in the dino-to-bird line but recent studies have shown that feathers probably went back much further down the tree than even dromeosaurids and avian dinosaurs, suggesting that even tyrannosaurids probably had some form of feathers. for instance, dilong paradoxus is an early tyrannosaurid that was found to have feathers. so a late tyrannosaurid like t. rex probably would have as well.
i kind of picture him looking a little like a vulture. a really big, really ugly vulture.

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arachnophilia
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Message 36 of 200 (279939)
01-18-2006 9:40 PM
Reply to: Message 35 by umliak
01-18-2006 6:57 PM


no, probably not. horner suggests that t. rex would have been quite ugly (like the vultures i mentioned) in order to help scare away other predators from their prey.
This message has been edited by arachnophilia, 01-18-2006 09:40 PM

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arachnophilia
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Posts: 9069
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Message 40 of 200 (287154)
02-15-2006 10:26 PM
Reply to: Message 37 by Mallon
02-15-2006 1:37 PM


Re: Ugh!
I wouldn't put too much faith in anything Horner says -- especially as it pertains to T. rex.
heh, yeah. he tends to be a little on the screw-ball side about that sort of thing. i think he's a little too staunch of a supporter for the scavenger-only idea of rexy. one could attain a more realistic perspective by comparing t. rex to modern equivalents, like the lion. in some parts of africa, primarily lions do the hunting and hyenas scavenge. in other parts, it's exactly reversed. i suspect that t. rex would probably have occupied both social roles: hunting when it could and scavengening when it could.
but i thought the vulture idea was interesting, especially since we're now pretty certain that tyrannosaurids had feathers.
- Cladistically speaking, humans are NOT classified as reptiles. We are derived from synapsids (the primitive ones informally known as "mammal-like reptiles"), essentially the sister clade to "reptiles".
well, yes. but the synapsid were reptiles at the time. we run into problems here and there with cladistics, if we only look in modern terms, because there aren't always modern varieties of things. where do we put dinosaurs? are theropod dinosaurs birds, or vice versa?
Interesting to note that some dinosaurs (oviraptorids, specifically -- Nomingia, more specifically) had pygostyles.
yes, quite. we see various avian features arising all over the place.
- It has been argued numerous times now that dromaeosaurids ("raptors") are, in fact, secondarily flightless birds, due to their being more bird-like than Archaeopteryx in some ways.
i was actually thinking of posting a thread about this. now that this thread has generated some more interest, i'll just post it here.
i don't know if i would call velociraptor or dienonychus a flightless bird. i'm also not sure how they are "more bird-like than archaeopteryx" either. skeletally, they share the vast majority of their features. the thing that makes archaeopteryx "special" is the feathers. we know it had them, but we don't know if dromeosaurids did (although it's VERY likely).
but i'd like to make a suggestion, in line with my "archaeopteryx is not a bird" stance. i'm starting to think that archaeopteryx isn't even remotely special -- just well preserved. there's a gene in modern birds that produces feathers. and there's a gene that takes SOME feathers and modifies them into scutes. we know this, because this is what happens when we turn off that second gene:
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 this puts feathers WAY before birds: they are no longer a feature that we can use to classify something as a bird. i'd like to further suggest that their origin would be around the time the first warm-blooded animals were evolving. since one of the primary functions seems to regulation of body temperature, this would make sense. the first dinosaurs we see are essentially small bipedal animals -- pushed away from the ground because they no longer require proximity to it for warmth. the large quadrupedal dinosaurs like stegosaurs and sauropods and the like all have early bipedal ancestors.
feathers therefore might be a better indicator that something is a dinosaur, though as i said we should expect to see feathers evolving BEFORE the dinosaurs in other reptiles like longisquama. longisquama is a curious reptile (archosaur? ... ?) that appears to have feathers:
we also know that pterosaurs had something like hair, which may mean that their ancestors had a step in the evolution of feathers as well, only used for warmth instead of flight.
so the next question is: what is a bird? skeletally, archaeopteryx and dromeosaurids aren't really all that that special either. they have back-turned hips, sure. but they're only slightly like even the earliest bird hip we have from the cretaceous. they have semi-lunate carpals and wishbones, which are great for flight, but no keeled breastbone for the flight muscles to attach to. neither has a reversed hallux, and both have fully formed theropod hands. although the bones are highly pneumaticized, they're not fused together in the right ways in the arms or legs.
archaeopteryx and other theropods represent a class of highly avian dinosaurs that share many (but not all) features with birds. they seem to be somewhat closely related to ancestors of modern birds, and are thus good indicators of how birds evolved. but i wouldn't call them birds quite yet. there are just too many differences in my eyes.


This message is a reply to:
 Message 37 by Mallon, posted 02-15-2006 1:37 PM Mallon has replied

Replies to this message:
 Message 41 by Mallon, posted 02-16-2006 8:30 AM arachnophilia has replied
 Message 68 by extremophile, posted 04-10-2006 1:50 PM arachnophilia has replied

  
arachnophilia
Member (Idle past 1452 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 42 of 200 (287479)
02-16-2006 9:53 PM
Reply to: Message 41 by Mallon
02-16-2006 8:30 AM


Re: Ugh!
Birds are definitely theropod dinosaurs, but not all theropod dinosaurs are birds.
quite -- i just don't think we can go dashing off calling all theropods "birds" willy-nilly.
For one thing, Velociraptor has uncinate processes -- a very birdlike feature (though seen in other reptiles as well). Other aspects of the pectoral girdle suggest bird affinities as well. Read any of Greg Paul's two books to learn more. He's the one pushing hardest on this front lately.
right, but that doesn't make it a bird. there are a lot of skeletal similarities, but as you point out many are shared by other reptiles, and very many by other theropods. and very few of those features are exactly the features of things that are definitively birds, just analogous, transitional features still much more similar to classical dinosaurian features.
i'm just arguing that birds are highly modified theropodal dinosaurs, but like you said, not all theropods are birds. the primary feature i look for in calling something "bird" is the clawless, fused digits of a bird wing. a "true" wing, as opposed to an arm and hand with flight-feathers like archaeopteryx. it doesn't even neccessarily have to be used for flight, just present in some form. modern flightless birds have wings, because their ancestors flew. the cretaceous "backwards/opposite birds" have wings as well, even if they were an evolutionary dead end.
I really don't think that bird 'scutes' (i.e. scutellate tarsi) are at all homologous to the bony scutes in ankylosaur skin, so I don't know how far that argument will get you.
well, it was just a suggestion. i think it warrants looking into.
I think you'll have a hard time arguing that those structures on Longisquama are real feathers if you look at them in detail. Some have even suggested they're just preserved fern fronds.
some have, yes. personally, i don't know. i looked for a few nights on various paleontology sites and fora, and couldn't find a definitive answer, just a LOT of debate. i found one high-resolution photo of the "feathers" on the internet, but it's way too blurry and grainy to look at any detail. it's obvious that there's a central vein and somewhat tightly arranged somethings coming off of it. if it's a ferm, it's kind of a strange arrangement (and size? can't tell) for a fern. but if it's a feather, it's still kind of strange.
but an extremely early evolution of feathers would be a good explanation for longisquama. and it fits in pretty close to the evolution of the earliest forms of warm blooded animals. i suspect that hair, feathers, and any other skin-coverings of keratin like beaks all share their basic developmental stage around this time. but i don't know. it's just a thought.


This message is a reply to:
 Message 41 by Mallon, posted 02-16-2006 8:30 AM Mallon has replied

Replies to this message:
 Message 43 by Mallon, posted 02-17-2006 8:49 AM arachnophilia has replied

  
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