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Author | Topic: Evolution of bird lungs from reptile lungs impossible? | |||||||||||||||||||||
arachnophilia Member (Idle past 1371 days) Posts: 9069 From: god's waiting room Joined: |
i think i might do a nice rebutal to this particular page in the other thread. it has some fun stuff like this:
quote: last time i checked, auks don't have teeth at all, and don't look remotely like an archaeopteryx. they don;t even hold their bodies the same way. also, i might point out that archaeopteryx has pointed teeth (like theropod dinosaurs) not flat ones (like what? elephants?) anyways, on to the obvious.
Ruben, John A, et al (1997). Lung Structure and Ventilation in Theropod Dinosaurs and Early Birds. Science 278(5341): 1267-1270. (Link to html version of Ruben et al 1997):http://cas.bellarmine.edu/...structure_and_ventilation_i.htm in which the authors claim this: "Recently, conventional wisdom has held that birds are direct descendants of theropod dinosaurs. However, the apparently steadfast maintenance of hepatic-piston diaphragmatic lung ventilation in theropods throughout the Mesozoic poses fundamental problems for such a relationship. The earliest stages in the derivation of the avian abdominal air sac system from a diaphragm-ventilating ancestor would have necessitated selection for a diaphragmatic hernia in taxa transitional between theropods and birds. Such a debilitating condition would have immediately compromised the entire pulmonary ventilatory apparatus and seems unlikely to have been of any selective advantage." if you scroll down to the second picture, the caption reads:
quote: so let's review. lizards/snakes = rid-breathers, with no diaphragm.bird = air-flow breathers, with no diaphragm. i don't see a problem here. still confirmed here:
quote: the article basically spends time arguing that theropods are crocodiles. theropods are NOT crocodiles. crocodiles are quite similar to the very primitive archosaurs, theropodal dinosaurs are quite different. the clincher, of course, is the picture of sinosauropteryx, which clearly shows a diaphragm. well, i won't cut and post the whole thing, but read an educated opinion on this: Dinosauria On-Line This message has been edited by arachnophilia, 10-11-2005 08:49 PM
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arachnophilia Member (Idle past 1371 days) Posts: 9069 From: god's waiting room Joined: |
If the theropods are air sac breathers then that adaptation can't have evolved to allow breathing cycles to be seperated from wing beats. Any other ideas for possible adaptive advantages? allow me to speculate. birds and theropods have a few key features in common. but for theropod dinosaurs, seeing these as adaptation for flight makes little sense. but when you look at an animal like velociraptor, it's pretty easy to see what it's adapted for: speed. when osborn found it, that's probably what he was thinking too. so we recognize without much thought that many of these "flight" features actually have very little to do with flight. for instance, backward-pointing hips allow for greater pull on the femur. leg proportion allows for endurance. hollow bones reduce body-weight, making for a more efficient run -- but the kicker is actually the lungs:
quote: unidirectional airflow = more efficient respiration = more O2 = faster running speed, for longer. i think we all see the basic evolutionary motivation behind it now. the velociraptor that could the run faster for longer catches the prey more often. added by edit: there's another good idea, as apparently pneumatized bones (and therefor air sacs) are very common in saurischian dinosaurs. see the post below. basically, it seems that this particularly lung structure was developed by early saurischian dinosaurs as method to cope with low oxygen. this later allowed the speed of velociraptor, but also warm-bloodedness, and eventually flight. it's a funny dispute, really. we're not actually debating bird evolution, we'e debating dinosaur evolution. the fact is that at least some dinosaurs DID breath this way, including theropods. arguments about how "impossible" this particular adaptation is to evolve doesn't really stop the dinosaur-to-bird theory, does it? This message has been edited by arachnophilia, 10-12-2005 06:40 PM
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arachnophilia Member (Idle past 1371 days) Posts: 9069 From: god's waiting room Joined: |
I see a major problem... micromutions resulting in the ability of the alveoli to exand and contract would not have a selective advantage over functional lungs... yes, it would free the cycle of breathing from the beat pattern of the wings, but it would result in less oxygen being utilized. As in other examples in nature, transitional forms would be less functional and thus would not survive. Your analogy is thus untenable. well, as i pointed out above, bird lungs are far MORE efficient that other tetrapod lungs. we actually breath rather inefficiently, mixing our oxygen and carbon dioxide. so any system that combines unidirectional flow and bidirectional flow is bound to be more efficient than bidirectional alone. let's look at one: the modern bird.
from above source: Bird Respiratory System see, it's a mistake to confuse the bird's lung with entire pulmonary system. the system itself is bidirectional. they don't breath through their rears. now, the lung itself is now shown in this picture ("for clarity"). but if i'm reading it right, the parabronchi go through it, and the neopulmonic (unidirectional) process occurs there. birds still breath in and out, and the air goes through the trachea just like every other tetrapod. the difference is that an instead of reversing, it does a little circle. all this fuss is basically about the way to make a u-turn. should we go around the block, or do a u, or do a three point? the significant thing about birds is that they're the only animals that go around the block. other than theropod dinosaurs, that is. we have evidence that dinosaurs not only had air sacs, but that they were integrated into the bone structure, like birds'. the other significant thing is that bird respiration is TWO-cycle, not just one like most other animals. the breath in to fill the posterior sacs, which exhale into the lungs for oxygen exchange. then they inhale the carbion dioxide into the anterior sacs, which are exhaled out of the body. it's the same basic process, doubled. i'd also like the point out that the primary system for moving air in birds is the rib-cage itself. birds are basically rib-breathers, like most reptiles:
quote: quote: and their lungs are pretty much the same too:
quote: the evidence is pretty much in favor of the ancient thecodonts being rid-breathers, and diaphramgs evolved separately in a few lines of reptiles, such as the crocodiles and the ancestors of modern mammals. but probably not in dinosaurs. a different set of features -- air sacs -- seems to have taken hold in them. however, the other option is not a problem either, really. air sac pressure could easily be used the same way a diaphragm is -- to expand and contract the lung itself. but there's a more likely candidate:
quote:
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arachnophilia Member (Idle past 1371 days) Posts: 9069 From: god's waiting room Joined: |
Wait a minute! Does that mean we have that "half-a-lung" that creationists say cannot exist? the short answer: yes. the long answer: no, we have a fully formed lung, but only half a respiratory system.
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arachnophilia Member (Idle past 1371 days) Posts: 9069 From: god's waiting room Joined: |
if i were to design a perfect creature, it would be very like a maniraptorian theropod.
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arachnophilia Member (Idle past 1371 days) Posts: 9069 From: god's waiting room Joined: |
this should probably go in the other thread.
The well-known ornithologists L. D. Martin, J. D. Steward, and K. N. Whetstone observed that Archæopteryx and other similar birds have teeth with flat-topped surfaces and large roots. Yet the teeth of theropod dinosaurs, the alleged ancestors of these birds, are protuberant like saws and have narrow roots.48 48 L. D. Martin, J. D. Stewart, K. N. Whetstone, The Auk, Vol 98, 1980, p. 86. quote: (creationists, in the other hand, could say that Spinosaurus can have different teeth because it’s a "kind" in his own, not a part of theropoda or anything) well, that's because they don't understand heirarchies. spinosaurus (and baronyx) are members of spinosauridae, which is a group of theropoda. they're just not coelurosauria -- which includes t. rex, velociraptor, and archaeopteryx. the best evolutionary guess (and one that looks like a good one to me) is that spinosaurs are the early cretaceous dead-end to earlier theropods like dilophosaurs. the pronounced "notch" in the upper jaw is quite similar. however, i feel the need to point out that spinosaur teeth DO have serrations, they are just very, very small. (i seem to recall reading somewhat recently that archaeopteryx had similar microscopic serrations, but i might be mistaken. i'll look and see if i can find anything) edit:
I know that he’s involved in the dino-bird debate, on the "birds are not dinosaurs" side the odd thing here is that unserrated teeth link archaeopteryx to birds. all known bird teeth are unserrated, unless we start counting feathered dinosaurs as birds. so to use this as a point in the debate, arguing that "birds are not dinosaurs" is to essentially argue that archaeopteryx is not a dinosaur. and i think that even an idiot could tell that it is looking at the skeleton. moreover, in the other thread, i detailed all of the things that MAKE archaeopteryx a dinosaur. the fact that it has features that are both avian and dinosaurian kind of defeats the argument that "birds are not dinosaurs." why point them out? This message has been edited by arachnophilia, 04-10-2006 07:41 AM
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arachnophilia Member (Idle past 1371 days) Posts: 9069 From: god's waiting room Joined: |
I wonder how bats compare as far as these "pre-requisites" are concerned. Anyone here knowledgable on this subject? How do bat lungs compare to bird lungs? heh, that would be beautiful. unfortunately, i don't know squat about bat. though i am pretty sure they lack the lung function of birds, considering that birds are the ONLY animals that breath this way. other than, apparently, theropod dinosaurs. there's the other reason this argument is totally specious: theropod skeletons contain, gradually, more and more of specialized fusing and hollowing of bones seen in birds. we know they had air-sacs, like birds. they have the right muscular and skeletal, and probably circulator system. while they're not neccessarily pre-requisites for flight, they do help -- and they apparently help land dwelling theropod dinosaurs, too.
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