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


Message 30 of 135 (598183)
12-29-2010 1:44 AM
Reply to: Message 29 by Tupinambis
12-29-2010 12:40 AM


Re: Arbitrary differences
tegu writes:
In regards to the definition of what a "bird" is, I'm just going to throw this out here. There were some rumblings not too long ago (a few years) about the idea of incorporating all of the birds into the reptile group, or folding the crocodilians and birds together into an archosaur group. Either way "Aves" would effectively cease to be its own MAJOR taxonomic group (more like "Squamata" within the group "Reptilia"). The ornithology professors flipped shits when they first heard of that though.
this is more than rumblings; it is now the majority viewpoint among paleontologists, and most biologists. ornithologists didn't particularly like it, at first, but the (vocal) opponents of "birds are dinosaurs" are a small minority in the ornithology community.
I personally support making a separate archosaur group since birds and crocodiles really aren't all that different
the issue is not really one of difference or similarity, but of heredity. all the evidence points to aves being a subclade of dinosauria, not a sister clade.
you might be able to find some information here or here.

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


Message 31 of 135 (598185)
12-29-2010 3:36 AM
Reply to: Message 22 by faith24
09-23-2010 6:49 PM


the avian respiratory system
faith24 writes:
Birds cannot move their thigh bone so they must bend their knee while walking or running. Land creatures such as the theropods can move their thigh bone. Also birds required more oxygen than cold blooded animals and so to supply this need, birds have special lungs and supporting musculature. If birds have the same muscle structure as the dinosaurs and could move their thigh, their lungs would collapsed.
what a load of sensationalist birds-came-first nonsense! allow me to break this down, point by point.


1. femoral movement in birds


while it might be true that femoral movement must be restricted (note: restricted, not prevented) in some flying birds to prevent collapse of the abdominal air sacs, this wold simply be a trade-off aimed at keeping flight muscles highly oxygenated. if there is really anything particularly to this idea at all, and i'm not convinced that there is. however, i know that when a bird relies more on use of its legs to survive, this condition is simply not found.
quote:
The anatomy and kinematics of the rhea pelvis and hindlimb are straightforward. The femur is subhorizontally and slightly laterally oriented and its distal end moves up and down during locomotion, while the tibiotarsus moves parasagittally. The long tarsometatarsus also moves parasagittally because the metatarsal ankle, like the knee, allows movement in only the fore-and-aft plane.
http://www.ldeo.columbia.edu/.../nbcp/padian_olsen_89_sm.pdf
rheas move their femora while running. this paper is a comparison between the gait and tracks of the modern rhea and theropod dinosaurs. it turns out that the ratite gait is very much like the dinosaurian one. further, here is a diagram of exactly how much an ostrich's femur rotates while running, from this article on ostrich locomotion.


2. the difference between the avian lung, and pneumatization


please note that i wrote "air sac" above, and not "lung". while it is common for creationist and birds-came-first-ist literature to group these two together, this would be a fundamental misunderstanding of evolution. it does not work in an all-or-nothing fashion, spontaneous generating whole ("irreducibly complex") systems of organs or organelles. rather, these things come into place piecemeal, and often scaffold. it is quite possible to have a partially avian respiratory system, without abdominal air sacs, or any of the other peculiar skeletal formations tied to the respiratory systems of modern birds. want proof?


3. evolutionary links


here's another animal that swings its femora even more widely, and has a lung similar to birds.
quote:
Peculiar to the crocodilian lung, however, is the tendency for monopodal - as opposed to dichotomous - branching of the chambers, as well as the tendency for this branching to occur at the bases rather than at the tips of the chambers (Milani, 1897; Broman, 1939). The closest affinity in these respects is seen in the pattern of formation of the secondary bronchi of the avian lung (Locy & Larsell, 1916; Perry, 1987). Further similarities between crocodilian and foetal avian lungs are the small number of cranial chambers (secondary bronchi in birds), their tendency to occur in a spiral row or rows, the lack of a medial row of cranial chambers and the large number of relatively loosely ordered caudal chambers. Furthermore, the tendency of crocodilian lung chambers to form arching, tubular structures is reminiscent of developing avian secondary bronchi and parabronchi (Duncker, 1978a). It is possible to construct an approximation of the avian lungair-sac system from the crocodilian structural type: sac-like cranial, ventral and caudal chambers become air sacs, dorsal or medial chamber rows arch caudally (with shortening of the proto-avian thorax), their chamber walls deepen to parabronchi which meet terminally in the plane of anastomosis with their counterparts from the caudal lung regions, and the parabronchial lumina become contiguous through perforations. Only the blood-air-capillary net remains exclusively avian.
Functional Morphology of the Lungs of the Nile Crocodile, Crocodylus Niloticus: Non-Respiratory Parameters | Journal of Experimental Biology | The Company of Biologists
get that one? crocodiles, more or less, have the same respiratory system as birds. neither crocodiles nor ratite birds collapse a lung when they run, and crocodiles have a completely different method of locomotion and skeletal arrangement. rather, it seems that avian flight condition evolved around and already developed respiratory system, which then became more reliant on specific adaptions for flight. these have secondarily lost in some flightless birds, such as ratites.
in fact, we find that many theropod dinosaurs, specifically the maniraptors, do indeed have partially pneumatized bones, and to about the same degree as modern ratites. this means velociraptor and even t. rex had thoracic and abdominal airs sacs, like flying birds -- just in a reduced capacity.


4. so how did this happen?


simple enough. something like the crocodilian lung existed in all dinosaurs, and progressed towards the avian lung in theropods. in flying dinosaurs, the air sacs simply greatly expanded, co-evolving with greater and greater flight capability. the earliest flying dinosaurs were not capable of extended powered flight, due in large part to their small sternums. they simply lacked the musculature. as they began to gain this musculature, they made a trade-off: more focus on flight, less on the ground. this trade-off allowed greater expansion of the abdominal air sacs -- but might have limited locomotion on the ground.
this is not a problem for the dinosaurian evolution of birds. not in the slightest.
Edited by arachnophilia, : No reason given.
Edited by arachnophilia, : additional article
Edited by arachnophilia, : sorry for the repeated and massive edits, but the more i look at this, the more the whole idea of the necessity of a restricted femur in any avian due to paradoxical collapse of the posterior air sacs.. is just a giant load of bullshit, all put forward by this one particular paper, quick & rubens (2009), with no real basis in anything. please see this blogpost for a strong critique: Page not found | ScienceBlogs

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


Message 32 of 135 (598186)
12-29-2010 4:03 AM
Reply to: Message 20 by faith24
09-23-2010 6:17 PM


faith24 writes:
You know, people always thought that birds evolved from dinosaurs.
you have misunderstood. and so have perhaps a few members of this forum.
birds did not "evolve from" dinosaurs. birds are dinosaurs. in the same way that a lizard is a reptile, or a frog is an amphibian, or you are a mammal. birds are dinosaurs. they are a highly specialized sub-group, but not a separate group.
Some suggest that the Archeopteryx is just a perching bird.
picture time!
(source)
that should settle it, right? not just a bird, much more like a dinosaur.
There are huge differences between birds and dinosaurs that it is impossible for birds to evolved from dinosaurs.
no. birds are dinosaurs. birds are highly specialized, yes. most of that specialization is in the form of ossification between bones, such as the digits becoming the carpormetacarpus. but many birds, such as rarites, retain some of the dinosaurian digits, and some, like the hoatzin, are even born with perfect maniraptoran hands, that looks nearly identical to those of a velociraptor.
i'm still confused because there are a lot of misinformation out there you don;t know which one to believe.
i suggest reading anything by greg paul.
What do you think about these birds foot print?
Geotimes - June 2002 - Bird Fossil Feet
i think they're pretty fantastic, don't you?

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


Message 33 of 135 (598187)
12-29-2010 4:23 AM
Reply to: Message 16 by Taq
09-21-2010 4:57 PM


faith24 writes:
This article seem to say otherwise about dino-bird evolution. Maybe it was the other way around?
http://www.physorg.com/news184959295.html
Taq writes:
It is speaking of a single species, microraptor. This doesn't mean that the analysis of this single species applies to ALL dino-bird intermediates.
it's talking specifically about pretty much all of dromaeosauridae.
there's an interesting idea, and goes something like this: all evidence points to archaeopteryx as being not only the earliest bird known to science, but also the earliest dromaeosaurid. the hyperextensible 2nd digit on the foot is a dead give-away. so, some suggest, that the last common ancestor between archaeopteryx and modern birds was also likely the last common ancestor between archaeopteryx and say velociraptor -- and that something like velociraptor secondarily lost flight. this view is apparently not popular among paleontologists.
however, this is not what that article is talking about. it's more "birds came first" nonsense, ala feduccia and co. they basically claim that theropods are not dinosaurs, they're birds, and they've magically converged with dinosaurs to nearly 100% homology. and that's just plain stupid.
There is strong evidence that non-avian dinosaurs had the same type of lung:
"Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina"
this is actually old hat. a paper like this doesn't show that dinosaurs in general had avian air sacs. we know that they did, and have known for a long, long time. rather, it shows that this particular new find has them. even t. rex had air sacs.

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


Message 35 of 135 (598245)
12-29-2010 6:27 PM
Reply to: Message 34 by New Cat's Eye
12-29-2010 10:58 AM


Re: Look at the feets!
Catholic Scientist writes:
The emu feet still have scales on them!
so, birds have two kinds of scales on their feet: reticulae (on the bottoms, the round reptilian scales) and the scutellae (flat plate-like scales on the top).
it turns out that the scutes have a strong relationship to feathers, and lacking a certain protein in development, become feathers. this likely means that birds have one gene that controls feather development all over their bodies, including their feet (such as in microraptor), and another that turns them off in particular places.
ie: the dinosaurian scales evolved from feather, not vice-versa.

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


Message 37 of 135 (598415)
12-30-2010 7:32 PM
Reply to: Message 36 by New Cat's Eye
12-30-2010 10:59 AM


Re: Look at the feets!
Catholic Scientist writes:
Its not that hard to imagine scales and feathers as being a variation of the same "thing". I always thought that feathers were just elongated scales but I guess I'll have to change that to some scales just being shortened feathers.
it's important to note that this is not more birds-came-first nonsense. it just shows that perhaps feathers are further down the dinosaurian family tree than previously thought. this has been confirmed recently, with the discovery of an ornithischian dinosaur with primitive feathers. the strong homology between tianyulong's feathers and theropod feathers indicates that feathers probably go back to before the divergence of saurischia and ornithischia. ie: the very earliest dinosaurs might have been walking around sporting similar proto-feathers, and feathers might even be a defining characteristic for dinosaurs (like hair for mammals). of course, they were probably lost secondarily in larger varieties.
in any case, i personally feel that feathers probably go back just slightly further than that, perhaps to basal archosaurs, and go hand-in-hand with the evolution of endotherms. for instance, pterosaurs sometimes have "hair" covering their bodies, and iirc, these "hairs" are strongly related to feathers -- they just didn't evolve into the flight surfaces and were strictly used for warmth.
also interesting is the fact that crocodiles have scutes. i'm not sure if these are related to feathers in any way, but wouldn't it be truly strange if the basal psuedosuchians were feathered, and the crocodiles lost their feathers secondarily to adapt better to an aquatic environment?
i am not a paleontologist, and at least some of these ideas would be very unpopular among actual paleontologists. i'm sure this is partly because they're generally used to support the aforementioned "birds came first" idea, which states that birds evolved in a separate lineage from basal archosaurs (something very lizard-like, actually), and theropods are not actually dinosaurs. which is so stupid, i can't even describe. see the links i posted above. i am very much not supporting this idea, because it stretches convergent evolution to the point of incredulity.

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


Message 51 of 135 (598528)
12-31-2010 9:10 PM
Reply to: Message 44 by Blue Jay
12-31-2010 3:39 PM


Re: Look at the feets!
Bluejay writes:
This seems highly unrealistic. Scutes clearly predate feathers in the fossil record. I think they even predate the diapsid-synapsid split, so it seems unlikely that feathers predated that.
I'm also highly skeptical because apparently none of the cited work by Alan Brush demonstrating that scutes happen when feather development is suppressed were published or peer-reviewed.
Also, I'm not sure that a developmental pathway defaulting to a certain end product is really evidence that that end product is the primitive condition. I'm no geneticist, though, so I could be wrong.
well, i knew someone would bring up the potential shortcomings of this idea. thanks for that. yes, i really don't know, but it's an interesting idea.
I could be convinced, however, if they could cause crocodilians to develop feathers instead of scutes using the same techniques.
yes, that would pretty cool. the question -- and i'd like to know too -- is whether or not crocodilian scutes are related to avian/dinosaurian scutes. it's entirely possible the avian ones are merely secondary adaptions and not actually related to scutes in other archosaurs at all. it's also possible that this particular gene was in place before the evolution of feathers, the secondary modifications of it is what caused microraptor to grow feathers on its feet.
i think it's an interesting area of study, and needs some more examination. in any case, the ornithiscian with proto-feathers certainly pushes feathers further down the family tree.
Edited by arachnophilia, : No reason given.

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


Message 54 of 135 (598537)
01-01-2011 12:01 AM
Reply to: Message 50 by Buzsaw
12-31-2010 9:02 PM


dinosaurs: more like birds than like crocodiles
pisture post!
1. Dinos and most modern reptiles are oviparous, producing eggs that hatch outside of the body.

crocodile egg

chicken egg
most reptiles are oviparous. most dinosaurs are oviparous. all birds are oviparous.
2. Crocodiles have similar abdominal ribs to dinosaurs.

crocodile gastralia

tyrannosaurus rex gastralia (from sue)
note: it's hard to see in the picture, i can't find an especially good depiction of it easily, but theropod gastralia interlock, and are much more diminutive than the giant plates of a crocodile. it should be noted that true gastralia are not typically found in reptiles -- except crocodiles.
3. no fur

sinosauropteryx "fur"
4. both reptiles whereas birds are not.
dinosaurs are reptiles much in the same way you're an amphibian. you're not cold blooded (i think), you don't go through any metamorposis, and you were born live. you don't need to be around water to keep your skin hydrated. similarly, dinosaurs are endothermic, covered in feathers, stand upright, etc. they don't hug the ground for warmth like a reptile -- they're the reason that "reptile" is not longer a scientifically recognized clade. they make "reptilia" paraphyletic. and your argument is just a little silly anyways, see as how birds are a subgroup of dinosaurs. if B is a subgroup of A, and C is a subgroup of B, C is a subgroup of A.
5. both land dwellers, unlike birds

ostriches in israel
all birds are ground-based. some live in trees. some on glaciers. none remain in the air constantly. some can't even fly.
6. small similar appearing heads and swishy tails, unlike birds.

dromaeosaur zygopophyses
while the dromaeosaurid (that includes archie's) tail is still somewhat flexible, it wouldn't have been very "swishy". i know they show the "velociraptors" in jurassic park swishing their tails about, but they would not have been able to do this. above is a photo of what those tails actually looked like: their pre- and postzygoopophyses are extended for several vertebrae, making their tails somewhat stiff, particularly towards the end.
compare this to the tip of a crocodile's tail, which must move readily side-to-side to power their travel through water, and to a bird's tail, in which the end is totally fused into a pygostyle. the only similarity to the crocodile's in length, and that gets drastically shorter in cretaceous birds, and not all at once.

tail length in dinosaurs/birds
as for heads,

saltwater crocodile skull
velociraptor skull

terror bird skull
crocodiles have vertically flattened skulls, which are good for lurking just under the water, while still being able to breathe and see above water. dinosaurs and birds have laterally flattened skulls.
7. Both cohabited whereas birds did not, according to conventional paleontology but not according to the Genesis record.
i'm not even sure what that's supposed to mean.
8. Both had teeth and more similar bone structures unlike birds

crocodile sketelon

archaeopteryx

bird
and i'll find you a picture of bone cross-sections, if you really like. birds and dinosaurs often have hollow bones; crocodiles do not.
9. Overall appearance of lizards, crocks, iguanas, etc more resemble dinos than birds.

"green" iguana

american alligator

archaeopteryx

mockingbird
dinosaurs look like what now? now, i know i detailed up above why archaeopteryx is clearly not "just a bird" and is very much a theropod dinosaur. but it's important to note just how much closer dinosaurs are to birds than they are to crocodiles. clearly, they are related to both.
Edited by arachnophilia, : No reason given.
Edited by arachnophilia, : background color on transparent .png
Edited by arachnophilia, : turns out, the "crocodile bird" is a complete myth.

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


Message 55 of 135 (598538)
01-01-2011 12:29 AM
Reply to: Message 52 by Blue Jay
12-31-2010 11:35 PM


Re: Comparing Similarities And Differences
Bluejay writes:
Birds are reptiles. And, even if they're not, you can't use the point you're trying to prove as evidence for the point you're trying to prove.
i was less than technical with buz. but i'll point here that the word you're looking for is "sauropsid". crocodiles, dinosaurs, birds, and turtles are sauropsids. "reptilia" is a paraphyletic group which specifically excludes birds by definition, and thanks to the re-organization of the cladistic trees, isn't especially appropriate anymore.
"reptilia" (from wikipedia)
Also, there are dinosaurs that have beaks!
well, ornithischian ones, anyways. i thought about going there, but since their beaks are simply convergent, and they're not especially closely related to the dinosaurs that lead up to birds, i thought it would be a little disingenuous.
Scientific record cites evolution as reason for leg differences and size.
indeed. a crocodile's amrs and legs have a very different function from those of a velociraptor.
What? You mean reptiles and dinosaurs lived at the same time and place, whereas birds didn't?
If so, you're wrong.
if that's what he means, it's quite silly indeed. all three lived in the cretaceous period.
Edited by arachnophilia, : background color on transparent .png image

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


Message 57 of 135 (598541)
01-01-2011 4:19 AM
Reply to: Message 56 by Dr Adequate
01-01-2011 2:26 AM


Re: The Crocodile Bird
ha! very nice. that'll teach me not to track down an original source for an image, and read the page. thanks for that correction, learned something new today.
anyways, in that case, i'll go ahead and take that image down. it was pretty pointless anyways -- i think we all know that birds and crocodiles are both currently alive and share habitats, and that at one time, birds, non-avian dinosaurs, and crocodiles were all alive and shared habitats.
i still have no idea what the heck buz's comment was supposed to mean, anyways.

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


Message 61 of 135 (598643)
01-01-2011 3:29 PM
Reply to: Message 58 by Buzsaw
01-01-2011 9:05 AM


picture time again
Buzsaw writes:
That one dino is considered bird
it's really substantially more than one dinosaur, buz. it's every bird that is considered a dinosaur. the same way that every primate is considered a mammal. and, on top of that, there are a whole host of non-avian dinosaurs with feathers. these are actually the ones we don't consider birds, proper. here are the ones we do.
doesn't mean birds are generally considered reptiles.
nope. as i posted above, "reptile" is a paraphyletic group, so this point is pretty moot. "reptile" is defined as the class of sauropsids (and basal amniotes) that excludes birds.
"reptilia" (from wikipedia)
that's the definition of the colloquial term, versus the cladistic tree. the colloquial definition means nothing, really, in terms of actual evolutionary origin. note that the diagram is missing "dinosauria", as it's really under debate whether or not dinosaurs should be considered reptiles, because they are so dissimilar from every other "reptile".
More objectively, from what I've read, the consensus is that they descended from dinos.
no, birds are dinosaurs. they are a highly specialized subgroup of dinosaurs, but they are dinosaurs.
My position that the Biblical record is correct would require many adjustments to the changed physique such as the flattened croc and gater heads, the rear claw in the foot for grasping smaller things, the leg structure, etc.
well, you can't argue with "it must have been a miracle" in the face of all the evidence that says exactly the opposite. crocodiles would have had to re-evolve several features, extremely convergently with other modern sauropsids. like, several digits.
Conclusion: there are not more similarities, by and large, of birds/dinos than reptiles/dinos. It's all assumed to accomodate evolution.
yeah, let's see that.

a. crocodile

b. coelophysis

c. compsognathus

d. archaeopteryx

e. velociraptor
so let's play, "one of these things is not like the other". keep in mind that one of these is a bird. another is a mostly-ectothermic "reptile". which one is the least similar? oh, and please note that, to be fair, i have included one of the most primitive dinosaurs, the mid-triassic coelophysis, so named for its bird-like hollow bones.
Edited by arachnophilia, : typo

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


Message 64 of 135 (598694)
01-01-2011 9:07 PM
Reply to: Message 62 by Buzsaw
01-01-2011 8:21 PM


nonsense
Buzsaw writes:
Dinos and modern reptiles whereas birds are not. - Debatable
Dinos are reptiles , unlike birds - Debatable
Both cohabited whereas birds did not, Both had teeth and more similar bone structures unlike birds - Debatable
buz, this is nonsense. i don't mean that your ideas are ridiculous. i mean, nobody knows what the heck you're even talking about. can you rephrase these in ways that make sense? for instance, your first statement lacks a verb.
dinos and modern reptiles are what whereas birds are not?
and what the heck do you mean by cohabited?
Overall appearance of lizards, crocks, iguanas, etc more resemble dinos than birds. By observation? Yes. Ask anybody on the street to look at lizards, iguanas, gators and crocks whether these by and large look more like dinos, both having swishy tails and similar looking heads than most birds and they will say that they do.
most people are idiots. further, most people think dinosaurs look like this:

deinonychus antirrhopus, the "velociraptor" (paul 1988) as depicted in "jurassic park"
and not this:

deinonychus antirrhopus, as it would have really appeared
if you show them the far more accurate depiction above, they will invariably say "bird". the fact of the matter is that people thought of dinosaurs as glorified lizards for quite a long time, and frequently depicted them styled after lizards. the fact that when you say "dinosaur" most people think of something very lizard-like does not mean that dinosaurs actually were lizard-like. it just means that people have had inaccurate preconceptions drilled into their heads.
Digits of birds and theropod dinosaurs found to be non-homologous. What has been assumed for the last two decades by prominent paleontologists turns out to be questionable, as is so often the case in the conventional science arena.
alan feduccia is not a good person to discuss regarding avian evolution. he's basically the crank of the paleontological world -- him and his cronies larry martin and john ruben. not only are they wrong, but they frequently tout their research as proclaiming things it does not ("birds came first!"). on top of that, none of them are actually arguing for what you would like: they're arguing that birds (and, ahem, theropod dinosaurs) are not actually dinosaurs, but evolved separately and convergently from archosaurs. none of them question evolution, nevermind that birds are theropods. just that they're dinosaurs. which, frankly, is dumb.
as for the specific points, here's greg paul on the subject (he's the "paul" i mentioned above, under the jurassic park picture).
quote:
I have now read the Burke-Feduccia Science paper (Science vol. 278, pg. 666) on the alleged nonhomology of theropod and bird hands -- a subject I have worked upon (1984a) -- and the supporting viewpoint by Hinchliffe (Science vol. 278, pg. 596). As I suspected, it gives no reason to challenge the fact that birds are as much glorified dinosaurs. Instead, we are seeing the last gasps of a dying hypothesis.
To start with, the fossil evidence clearly shows that the outer digits are lost in theropods, leaving only I-II-III in avetheropods, with I always being a strong, big clawed thumb weapon (except when the arm is hyper-reduced). In herrerasaurs V is a wee splint and IV is just two small bones. There is no practical way to make IV into a strong finger with five bones including a large claw, while losing the big thumb, etc.
The anti-dinosaur group keeps stressing that digits are normally reduced symmetrically, and that this should be true of birds as well. Of course in the next breath they acknowledge that dinosaurs lost only the outer fingers, so there is no reason the other group of bipedal archosaurs, the birds, could not have done the same.
The basic problem is that even in the earliest bird embryos there are only four digits, the fifth is entirely lost. If there were five digits and we could watch which ones were lost there would be no problem. As it is there is currently no way to reliably number the digits in bird embryos. Doing so requires a number of untestable assumptions.
At the same time, we do not have any avetheropod embryos to examine. It is quite possible that they grew their fingers in exactly the same manner as baby birds, with the well developed digit opposite the ulna being III, rather than IV as is common in other tetrapods. After all, in adult avetheropods the digit opposite the ulna IS number III.
Why the avetheropod-bird clade would initially emphasize the development of III rather than IV is obvious. Loss of digit I in even the embryos would leave a big gap between the pisiform in the side of the wrist and metacarpal IV, unless the other digits shifted laterally. So IV would be were V was, and III would be were IV was. If the shift is not made from the get go, it is only going to have to occur at some point later. Also, IV will be entirely lost. To follow the usual tetrapod finger growth pattern would require IV to grow large in embryos, then be completely lost later on (Burke & Feduccia say that some lizards sharply reduce the size of IV, but it is not completely lost. Does anyone know what happens to digit IV in horse embryos?) This would be a waste of growth energy, and natural selection does not work to make finger buds convenient for embryologists to count, but to maximize efficiency of growth. The severe asymmetry of finger growth in theropods-birds should have forced them to reconfigure the growth pattern, so that III is initially emphasized rather than IV, and the latter is never more than a stub before it is eliminated.
The problem is that some embryologists expect digit IV to be large because it is so in animals with symmetrical finger reduction, and some want it to be IV, so they say it is, even though strong asymmetric finger growth could be expected to result in important changes in embryonic growth. As it is, there is no conclusive evidence that birds retain digits II-IV rather than I-III, there is no way to compare avian and dinosaur hand embryology, and so the problem is untestable.
Another thing the anti-dinosaur group does not have is a fossil record that in any way supports symmetrical reduction of fingers in protoavians. Of course this is because nondinosaurian ancestors of birds did not exist! There is a wonderful fossil trail of asymmetrical finger reduction in dinosaurs leading to the avian condition.
Science is always partly political, and it is important to understand the deep bias of some against birds being dinosaurs. For example, Feduccia (1996) claims that the hand of Archaeopteryx "does not closely resemble that of a theropod dinosaur." This when the [bird]'s long raptorial hand with a semi-lunate carpal block, and three gracile digits, is clearly a diminutive version of a dromaeosaur manus! Feduccia cannot point to any nondinosaur that has a hand anything at all like those of birds.
(source)
just to illustrate how truly dumb this is, let me again post pictures.

deinonychus

archaeopteryx

hoatzin chick (modern bird)

hoatzin adult (modern bird)
easy to see now? the digits are pretty clearly the same. this different numbering is an arbitrary thing that ornithologists have done because they assumed that birds lost their other digits symmetrically, where as paleontology shows that they did not.
Too often scientists see what they want to see
ruben? yeah, i saw a documentary which covered his incredibly ludicrous reconstruction of microraptor gui. i posted it on my blog a while back, and i will now re-post it here.

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 Message 62 by Buzsaw, posted 01-01-2011 8:21 PM Buzsaw has not replied

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


Message 65 of 135 (598696)
01-01-2011 9:15 PM
Reply to: Message 62 by Buzsaw
01-01-2011 8:21 PM


the dinosaur with four wings
Too often scientists see what they want to see
so, since you brought up ruben and martin's just plain silly reconstruction of microraptor, i thought i would re-post this entry from my blog, originally posted sept 21. 2008, after viewing a documentary in which martin appeared.
please note that this is a blog entry, but it's full of useful links and pictures. please note martin's hilarious reaction to seeing the proper scientific reconstruction of microraptor, and how he very obviously only sees what he wants to.
quote:
the discovery channel aired a documentary the other night on microraptor called the four winged dinosaur, originally a production by NOVA for PBS. microraptor is a dinosaur that i find especially interesting, not so much because it further provides evidence for the dinosaurian evolution of birds, but because of the complications it presents to that theory. microraptor is also very curious in that it has four wings. as you can see in the above picture (the m. gui holotype specimen), it has rather long flight feathers protruding from its feet.
how exactly such an animal flew (or if it flew at all) is quite the puzzle, and i have never found either proposal quite satisfactory. i think we can discard the "default" positions, legs tucked up underneath the body like a bird, and legs extended downward like a theropod dinosaur, because neither position uses the flight feathers at all. there have been two major hypotheses regarding how microraptor used its hind wings.
flat

this is the model that xu xing initially proposed when he first named microraptor. this model duplicates the way a flying squirrel would glide. but there a major problem with it, other than the fact that it looks just a little silly: dinosaurian hips are designed for forwards and backwards motion, not leg splaying motion. the documentary points out something along these lines, stating that dinosaurs evolved upright posture from their crocodilian ancestors who splayed their legs wide. you would have dislocate microraptor's hip joint for it to maintain that posture. even xu admits that this proposal is "probably wrong."
biplane

this is the more recent proposal, i believe first put forth by sankar chatterjee (somewhat known for his erroneous hybrid fossil reconstuctions). it was developed by trying to maintain a more bird-like posture, while still using the flight surfaces. this model is even more strange, and in my opinion, a good deal more silly. the flight feathers on the feet lack a strong leading edge, and would simply flutter in the wind too much to provide lift.
i've never found either idea particularly satisfactory. the program promised wind tunnel testing of a fully articulated and posable model of microraptor, so i was rather excited to see what conclusions they'd draw.
now, the dinosaurian origin of birds has been hypothesized since the very first discovery of a dinosaur. early paleontologists recognized right away that the hip structures of dinosaurs were very similar to birds, and that the three toed foot of the theropods was almost identical to a bird's foot. when archaeopteryx lithographica was discovered, a dinosaur with many bird-like features most prominently including flight feathers, it verified the link. the creationist objection at the time was that this was obviously a dinosaur that someone had carved feathers around. this was 1861. now they claim it's "just a bird" which is an even moe silly proposal. but archaeopteryx remained largely forgotten, as a curiosity and a footnote until the 1970's when john ostrom uncovered deinonychus antirrhopus. he noted many similarities between the two specimens, and the modern idea of the relationship between birds and dinosaurs began to take shape.
deinonychus also changed the way we think of dinosaurs. it's impossible to look at this animal and think "slow cold blooded lizard." until the 70's, this had been the preconception. but deinonychus just looks fast. and its tail is rigid; it can't be dragged on the ground. this was a warm-blooded, fully upright, counter-balanced, running predator. after the documentary covers the basic history of avian/dinosaur paleontology, it makes the obligatory jurassic park reference, showing pictures of their raptors. more on this later.
now, archaeopteryx and deinonychus and their high degree of similarity form pretty conclusive evidence that birds are dinosaurs, and other similar dinosaurs continue to back this up, even before microraptor is discovered. but we're continually discovering more and more dinosaurs with feathers, especially highly derived theropods. even tyrannosaurs seem to have been feathered at least in some regard. the only real debate regarding the origin of flight is whether flight evolved from ground up in running/flapping theropods, or from the trees down in aboreal gliding theropods. microraptor complicates the issue, because it is so closely related to running theropods, but must be arboreal due to the difficulty it would have walking with its enormous flight feathers on the hind limbs.
but cue the crackpots. perhaps my biggest problem with science journalism, even the better examples such as this, is the apparent need to be fair to all points of view. they give equal time to even the most ludicrous of viewpoints. including the non-dinosaur origin of flight. there is so much going against the idea (like, all the dinosaurs that are strongly homologous with birds, and all the dinosaurs with feathers), and the view is held by almost no one in the scientific community. you will likely find more flat-earth geologists than "birds are not dinosaurs" paleontologists. until the other night, i was only aware of one scientist against the dinosaurian origin of birds, alan feduccia. his name gets laughs in the paleontological world; he's not a paleontologist, he's an ornithologist. so he's easy to write off. his claim that paleontologists do not know much about birds is petty silly, too. because birds and crocodiles are the closest living relatives of dinosaurs (something even feduccia would concede), dinosaur paleontologists spend a lot of time studying our avian friends. it's feduccia that does not know much about dinosaurs.
but the documentary introduced dr. larry martin (center), a paleontologist who says of microraptor "you have just shown me the death of the dinosaur origin of birds" (paraphrased from memory). he and his assistant are working on their own model, taken directly from casts of the holotype specimen of m. gui (shown at the top of this post). their model is a splayed-leg quadruped, which they claim is not even a dinosaur. they question the other model, produced for the AMNH under the direction of xu xing and mark norell, as an artistic and subjective interpretation. "if you call matching it to 1/1000th of a mm on sixteen different specimens 'subjective' that's up to you," (also paraphrased from memory) says the artist who made it. martin looks at the AMNH model, which physically cannot splay its legs, and immediately claims it was fudged to support the dinosaurian idea. the documentary rather quickly and a bit too civilly trashes this idea, showing that the martin holotype cast is rather flattened. and in an amazing close up it shows that the martin model doesn't even fit together because the hip bones are too flattened, and that even if it tried to splay its legs, the femoral ball would pop away from the socket joint. oops, who's fudging things now?
as they show the close up shot of the hips and the femur, the fully ridiculous nature of martin's argument strikes me, and for reasons other than the joint's ability to spread open.
  1. even if it could splay, there's no good reason that a dinosaur couldn't secondarily evolve such an ability. this idea would be far, far more elegant than a splayed-leg arboreal lizard convergently evolving hundreds of features exactly identical to dinosaurs, including the lower-branching dinosaur clades martin proposes that archaeopteryx and descendants like velociraptor are not related to.
  2. it's not built like a splayed-leg crocodilian archosaur, or even a semi-upright pseudosuchian. those animals are flattened vertically, so they can walk with their bellies close to the ground. microraptor's hips are very tall and flattened laterally, something that is completely incompatible with an animal that splays its legs. it's a bit like supposing sailboats that travel on land, with the base of their hulls at ground level. where does the keel go, exactly? a splayed microraptor would leave a trench cut out by its pubic bone wherever it went.
  3. dinosaurs (versus non-dinosaurs) are actually identified on a good deal more than their posture. the most obvious factor is, of course, the hip complex. it's the hips that indicate an animal must be upright, not just the joint. further, the hips actually indicate what kind of dinosaur an animal is.
even discarding the femur (the very similar a. lithographica pictured), i'd look at the pubis (blue), determine that it's not forked, and look at the shape of the ilium (pink), and classify the animal as a saurischian dinosaur. then i'd notice the knob on the end of the pubis, and determine it's a theropod. further, because the pubis is backturned, i'd immediately conclude that it was a dromaeosaurid dinosaur, probably a deinonychosaur. guess what the scientific consensus is? and i'm a layman. why can't you figure this out, mr. ph.d. paleontologist?
back to the legitimate ground-up/trees-down debate, and the wind tunnel testing, the AMNH team determined that microraptor did not generate enough lift to fly with just its fore-wings, and the biplane model was also a no-go. too much drag, not enough lift, and pitches upwards rather quickly, resulting in even less lift. after some head scratching, xu proposes his secret weapon of a hypothesis: that it would extend its legs all the way behind it, making the feathers meet around the base section of the tail. nobody thinks it will work, but it turns out to generate the most lift and the least drag by far. xu wins all the bets, but he's had the most time to think about it.
this idea makes the most sense for a number of reasons. if microraptor pushed off of trees, its legs would naturally end up in this position. the placement of the feathers roughly duplicates the placement of a modern bird's tail feathers, only inside out. microraptor would then be able to shift through the various biplane formations, causing a pitch upwards to meet the next tree feet-first. this feet-first dragging roughly duplicates the fishing behaviour of modern eagles, with a similar usage of their leg feathers to create drag (right). i now consider this problem solved to my satisfaction.
the problem regarding trees-down v. ground-up remains unsolved, but i suspect that flight evolved and was secondarily lost numerous times. so the answer might be "both." greg paul suggests in predatory dinosaurs of the world that animals like velociraptor (pictued right with protoceratops) maybe have evolved from flying ancestors of birds, and not vice-versa. microraptor helps demonstrate this fairly clearly. genetically, even in modern birds, scutes (foot scales) are secondary adaptations of existing feathers such as m. gui's. this creates another curious problem in that a. lithographica, an earlier banch in the tree, appears to only have flight feathers above the ankle. so whether m. gui's method of flight is representative of the initial development or simply a re-development is not currently known.
about jurassic park

since i mentioned it above, it's worth saying a few more words about. when jurassic park came out 15 years ago, it was the most scientifically accurate dinosaur movie ever. today, it doesn't hold up so well. watching it somewhat recently, i was actually surprised at just how many errors there were. the documentary glosses over one by correctly discussing deinonychus while showing clips of jurassic park's "velociraptors." they mention that the only noticeable issue is that they should have had feathers. we now know that v. mongoliensis (and presumably d. antirrhopus) had flight feathers on its wings, like many other similar theropods. well, even in just the clips they showed, i was able to spot a few more errors.
  • that they don't have feathers is actually a much more complex point. michael crichton evidently read greg paul's aforementioned "predatory dinosaurs" book, as it's paul who proposes that "velociraptor" is a synonym of "deinonychus" and refers to d. antirrhopus as "velociraptor antirrhopus." this is the dinosaur that crichton intends for his book, as it matches the size and geographic locations. all species of velociraptor are dog-sized asian theropods. d. antirrhopus is a man-size north american theropod. however, he apparently only took cues from paul selectively, as every single depiction of either dinosaur in paul's book has feathers. this is, in fact, part of the main argument of the book.
  • the "raptors" of the movie are consistently depicted with bent wrists, palms facing downward and backward (as above). while maniraptors have incredibly flexible wrists (for dinosaurs) due to their semi-lunate carpals, they would still have to physically break their arms to hold them this way. the proper position is palms inward. think of bird wings, not human arms.
  • not shown in the clips, the movie makes mention of deinonychosaurids gutting their prey with their sickle-shaped claws on their second toe. we now know that they simply couldn't have done so because they lack the necessary muscle and bone strength, and the slashing edge on the claw. they probably went for the throat (jugular, coratid, or trachea) in a much more precision fashion, as shown in the "fighting dinosaurs" above.
i mention this last part because it probably provides a good use for their diminutive flight feathers, and possibly an answer to the trees-down vs ground-up dilemma. as raptors generally could flap, at least in part, the wings could be used as both lifting aids, and a distraction to get a surprised ceratopsian prey to turn its head and show its weak spot, while the raptor jumps in feet-first like a landing microraptor. after the rather terrifying displaying of flapping, it could grab on to a frill with its hands, effectively blinding its victim with the wings, and go for a precise puncture kill. then it could flap off, get away to safe distance, and wait for the prey to bleed out. it'd be sort of like a big scary cock fight. and powered flight in modern birds might have evolved from this behaviour in terrestrial dinosaurs, partially derived from the behaviour of gliding dinosaurs like m. gui.

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This message is a reply to:
 Message 62 by Buzsaw, posted 01-01-2011 8:21 PM Buzsaw has replied

Replies to this message:
 Message 66 by Buzsaw, posted 01-01-2011 10:25 PM arachnophilia has replied

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


Message 68 of 135 (598717)
01-01-2011 11:34 PM
Reply to: Message 66 by Buzsaw
01-01-2011 10:25 PM


running, and digits
Buzsaw writes:
In the Wyoming Rocky Mtn region where I grew up and on the desert I've seen some really fast little miniature somewhat dino looking lizzards which dart around likity split.
for very, very short bursts of speed, yes. no "reptile" is an endurance runner. they simply aren't built for it. iirc, the side-to-side running motion actually impairs respiration in reptiles. (perhaps a herpetologist can comment?) but this is definitely not the case in a dinosaur -- their respiration is actually aided by their running. this is the primary advantage that allowed them to become the dominant lifeforms in the mesozoic. the could out-endure any of their prey.
look at how a crocodile hunts, vs how an ostrich avoids being eaten. the crocodile is an ambush predator. if it doesn't catch you in the first snap, it simply gives up. they don't give chase. the ostrich will keep running, and running, until it's safe.
Assuming the accuracy of the Biblical record, the dino reptiles pre-flood would have likely been very lively, given the perfect warm climate that is implicated before the flood changed things.
so, this is a science forum, buz. we can't just assume things like the accuracy of the bible, or even that genesis is a record of anything. plus, dinosaurs lived in cold climates, too.
Perhaps I missed it but what about the study which I cited about the non-homogeneous digits of dino & bird?
it's nonsense, from "birds came first" ornithologists and crackpots. they assume that birds would have lost their digits symmetrically, and thus they cannot be homologous to the theropod hand, which is non-symmetric. this is obviously a bad assumption for a number of reasons:
  1. the theropod hand is homologous to the avian carpometacarprus
  2. hoatzin ontogeny recapitulates this particular development, and hoatzin are born with hands that have freely moving digits, claws, and are nearly exactly identical to a maniraptoran hand, except for some extra wrist bone fusing
  3. there is a very strong and convincing history of the evolution of the carpometacarpus, with all kinds of transitional forms, that shows precisely which digit is which, all the way from herrerasaurs (with five digits) to theropods (generally with three) to birds (with essentially one).
there is an excellent rebuttal by greg paul, above, in post #64. it goes back this far because, remember, these "birds came first" crackpots deny that theropod are dinosaurs, not that birds are theropods.

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This message is a reply to:
 Message 66 by Buzsaw, posted 01-01-2011 10:25 PM Buzsaw has replied

Replies to this message:
 Message 91 by Buzsaw, posted 01-04-2011 8:40 PM arachnophilia has replied

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


Message 70 of 135 (598721)
01-02-2011 1:04 AM
Reply to: Message 69 by Blue Jay
01-02-2011 12:43 AM


Re: Comparing Similarities And Differences
Bluejay writes:
Actually, I was picturing oviraptorids when I wrote that. Now that I think about it, it is kind of a disingenuous comment, given the homology implications. I probably should have avoided that.
oh, yes, right. oviraptors. heh, i knew i was forgetting something obvious. oviraptors are closely related to the origin of birds, though the beak is still somewhat convergent, as birds come from the non-beaked theropods. so, that's not nearly as disingenuous as the psittacosaurus picture i almost posted.
so, uh, carry on. don't mind me.
I tend to avoid the sciencespeak entirely with Buzsaw.
i know what you mean. but it's important to note (and i've pointed it out directly to him as well) as he keeps throwing around this "reptile" term, when "reptile" is really just an a completely arbitrary term that excludes birds and possibly dinosaurs by definition, and has no real relationship to any particular clade.

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