Albatrossity2
Posts: 2780
Joined: Mar. 2007
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Here's a good one.
On p. 137 of EE, the authors argue that the radical transformation of the lung from reptilian to avian seems improbable. Part of the argument goes like this. | Quote | | Finally, what happens to the diaphragm? The reptiles thought to be the ancestors of birds almost certainly had a diaphragm breathing system (footnote 8). According to many evolutionary biologists, changing from a diaphragm lung system to a flow-through lung would require changing and increasing the musculature of the reptile's chest. At the same time, the diaphragm would need to gradually go away. This poses a fundamental problem. Evolutionary biologist John Ruben points out that the earliest stages of this transformation would have required a hole or hernia in the reptile's diaphragm. This would have immediately compromised the entire system and led to certain death for any animal unfortunate enough to possess this non-functioning intermediate structure. |
Footnote eight refers to Ruben, et al. 1997, Science 278:1267-1269 (actually 1267-1270, at least in the reprint form that I have), and quotes from the article. | Quote | | "Therapod (sic) dinosaurs, like modern crocodiles, probably possessed a bellows-like septate lung, and that lung was probably ventilated...by a hepatic-piston diaphragm". |
That tell-tale ellipsis. What was elided? From the original paper | Quote | | These observations, combined with the occurrence among theropods of a distinct, relatively vertical, crocodilelike, highly elongate pubis (Figs. 4 and 5), as well as well-developed gastralia, provide evidence that theropod dinosaurs, like modern crocodiles, probably possessed a bellows-like septate lung and that the lung was probably ventilated, at least in part, by a hepatic-piston diaphragm that was powered by diaphragmatic muscles that extended between the pubic bones and liver. |
So the authors omitted something which might have led an inquiring student to conclude that perhaps something else was involved in breathing in the intermediate stages between the reptile lung and the bird lung. Inquiry-based? Not hardly.
But is that the whole story? No, their deception goes another level down. Ruben does not say anything about possible other mechanisms for bridging this anatomical/physiological gap, even though there might be some. Ruben is basically arguing in this paper that the theropod dinosaurs are not the earliest ancestors of birds, based on the problem with defining this intermediate. | Quote | | 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." |
In other words, he is not saying that this poses an insurmountable obstacle for any theory that postulates evolution of the bird lung, he is saying that this argues against the theropod-bird ancestral connection. Birds (with their unique lungs) must, by his logic, be descended from other ancestors.
Whether one agrees with that logic or not, I suspect that Ruben would be steamed at this use of his Science publication...
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Flesh of the sky, child of the sky, the mind
Has been obligated from the beginning
To create an ordered universe
As the only possible proof of its own inheritance.
- Pattiann Rogers
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