Evolution of bird lungs from reptile lungs impossible?

Ah... I see.

O'Connor, PM and LPA Claessens (2005). Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs. Nature 436, 253-256.From the abstract:quote:
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Birds are unique among living vertebrates in possessing pneumaticity of the postcranial skeleton, with invasion of bone by the pulmonary air-sac system1, 2, 3, 4. The avian respiratory system includes high-compliance air sacs that ventilate a dorsally fixed, non-expanding parabronchial lung2, 3, 5, 6. Caudally positioned abdominal and thoracic air sacs are critical components of the avian aspiration pump, facilitating flow-through ventilation of the lung and near-constant airflow during both inspiration and expiration, highlighting a design optimized for efficient gas exchange2, 5, 6, 7, 8. Postcranial skeletal pneumaticity has also been reported in numerous extinct archosaurs including non-avian theropod dinosaurs and Archaeopteryx9, 10, 11, 12. However, the relationship between osseous pneumaticity and the evolution of the avian respiratory apparatus has long remained ambiguous. Here we report, on the basis of a comparative analysis of region-specific pneumaticity with extant birds, evidence for cervical and abdominal air-sac systems in non-avian theropods, along with thoracic skeletal prerequisites of an avian-style aspiration pump. The early acquisition of this system among theropods is demonstrated by examination of an exceptional new specimen of Majungatholus atopus, documenting these features in a taxon only distantly related to birds.Taken together, these specializations imply the existence of the basic avian pulmonary Bauplan in basal neotheropods, indicating that flow-through ventilation of the lung is not restricted to birds but is probably a general theropod characteristic.This message has been edited by Rahonavis, 09-14-2005 07:32 PM

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"I still say a church steeple with a lightning rod on top shows a lack of confidence"

"Initially birds evolve to breath by expanding/contracting the air sacs rather than the lungs: this is beneficial because it frees the cycle of breathing from the beat pattern of the winds."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.

Why would it result in less oxygen being utilised? The lung capacity is not being reduced in any way. Incidently, some snakes breathe by expanding/contracting the air sacs and drawing air into the lungs that way so we know the method is, in principle, functional.

Interesting, thanks.

i think i might do a nice rebutal to this particular page in the other thread. it has some fun stuff like this:

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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

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48 L. D. Martin, J. D. Stewart, K. N. Whetstone, The Auk, Vol 98, 1980, p. 86.

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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. if you scroll down to the second picture, the caption reads:

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Fig. 2. Correlation of body cavity partitioning and lung ventilation mechanism in amniotes. Among modern amniotes, only mammals (A) and crocodilians (B) utilize active diaphragmatic lung ventilation. Active diaphragmatic breathing necessitates a complete vertical separation of the pleuro-pericardial cavity from the peritoneal (abdominal) cavity. In modern birds (C) and lepidosaurs (such as lizards and snakes), there is no similar separation of the body cavity. Lepidosaurs are exclusively costal (rib) breathers; extant birds possess a unique flow-through lung ventilated in large part by the elevation and depression of the sternum.

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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:

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Birds, like lizards, rely primarily on costally powered lung ventilation and lack a crocodilelike or mammallike thoracic-abdominal subdivision of the visceral cavity

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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-LineThis message has been edited by arachnophilia, 10-11-2005 08:49 PM

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אָרַח

Although, thinking about it, this would debunk part of my suggested evolutionary path. 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:

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The air sacs permit a unidirectional flow of air through the lungs. Unidirectional flow means that air moving through bird lungs is largely 'fresh' air & has a higher oxygen content. In contrast, air flow is 'bidirectional' in mammals, moving back & forth into & out of the lungs. As a result, air coming into a mammal's lungs is mixed with 'old' air (air that has been in the lungs for a while) & this 'mixed air' has less oxygen. So, in bird lungs, more oxygen is available to diffuse into the blood.

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Bird Respiratory System

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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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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 Systemsee, 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:

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During inspiration:
the sternum moves forward & downward while the vertebral ribs move cranially to expand the sternal ribs & the thoracoabdominal cavity (see diagram below). This expands the posterior & anterior air sacs (see 1 above) & lowers the pressure, causing air to move into those air sacs.

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During expiration:
the sternum moves backward & upward & the vertebral ribs move caudally to retract the sternal ribs & reduce the volume of the thoracoabdominal cavity. The reduces the volume of the anterior & posterior air sacs (see 2 & 4 above), causing air to move out of those sacs.

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(same source)

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Indeed air sacs and associated features at the tail end of the abdominal cavity are known to have developed in chameleons, snakes and certain types of lizard and this indicates that the tail end of the lung in the entire sauropsid (a group that includes birds and most reptiles and dinosaurs) is able to develop air sacs and invade the tail end of the skeleton.

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Bird Lung

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and their lungs are pretty much the same too:

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Although the ventilation of bird lungs is similar to that of reptiles, their effectiveness is increased by the presence of air sacs. Although no gas exchange occurs in the air sacs, their arrangement increases the efficiency of lung ventilation by enabling fresh air to pass through the lungs during both inhalation and exhalation.

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http://users.rcn.com/.../BiologyPages/V/VertebrateLungs.html

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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:

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Ultra-Low Oxygen Could Have Spurred Bird Breathing System -- Recent evidence suggests that oxygen levels were suppressed worldwide 175 - 275 million years ago, low enough to make breathing the air at sea level feel like respiration at high altitude. Peter Ward, a University of Washington paleontologist, theorizes that low oxygen and repeated short but substantial temperature increases because of greenhouse warming sparked two major mass-extinction events. In addition, he believes the conditions spurred the development of an unusual breathing system in Saurischian dinosaurs. Rather than having a diaphragm to force air in and out of lungs, the Saurischians had lungs attached to a series of thin-walled air sacs that appear to have functioned something like bellows to move air through the body. This breathing system, still found in today's birds, made the Saurischian dinosaurs better equipped than mammals to survive the harsh conditions in which oxygen content of air at the Earth's surface was only about half of today's 21%. "The literature always said that the reason birds had sacs was so they could breathe when they fly. But I don't know of any brontosaurus that could fly," Ward said. "However, when we considered that birds fly at altitudes where oxygen is significantly lower, we finally put it all together with the fact that the oxygen level at the surface was only 10 - 11% at the time the dinosaurs evolved. That's the same as trying to breathe at 14,000 feet. If you've ever been at 14,000 feet, you know it's not easy to breathe," he said.
Ward presented his ideas at the 2003 annual meeting of the American Geological Society in Seattle. See:

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Nature - Not Found & UW Homepage

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we actually breath rather inefficiently, mixing our oxygen and carbon dioxide.

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Wait a minute! Does that mean we have that "half-a-lung" that creationists say cannot exist?

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"Intellectually, scientifically, even artistically, fundamentalism -- biblical literalism -- is a road to nowhere, because it insists on fidelity to revealed truths that are not true." -- Katha Pollitt

the short answer: yes.the long answer: no, we have a fully formed lung, but only half a respiratory system.

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אָרַח

excellent example of another superior design of a feature that should be incorporated into other "more developed complex" designs -- IFF intelligent design mechanisms were in operation.

if i were to design a perfect creature, it would be very like a maniraptorian theropod.

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Larry D. Martin is an ornithologist?I know that he’s involved in the dino-bird debate, on the "birds are not dinosaurs" side, but I thought his speciality were sabre toothed cats, so he would more likely be a mammalogist...Anyway, the issue with the teeth difference, as far asI know, is that bird’s teeth are not much "knife-like", but rather needle-like, and so (or closer to that) have crocodilians. I don’t think that’s much of a problem because even Spinosaurus have teeth that is more like that. Also, I think that the dentitions of birds are not well known; could be that their teeth was a sublty reshaped neoteny (or pedomorphy, I never know which is which), it is, the conservation of theropod first or second dentition, which, according with one thing I saw (unfortunately, on TV) was a bit different from the definitive dentition. However, once I asked about that on a email list, and a guy said that there is not much known difference between theropod dentitions during development, and that bird dentitions are not very well known, or at least that he did not know.(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)

this should probably go in the other thread.

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Maxillary and dentary teeth reduced in size and number (or lost), with unserrated crowns and enlarged roots that completely enclose replacement teeth within them [many of the smallest theropod teeth are unserrated, which may be a developmental constraint. The pinched roots of bird teeth are similar to those of troodontids, basal ornithomimosaurs, and (in at least a couple of cases) dromaeosaurids].

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Dinosauria On-Line

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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: 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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