Field of Science

Evolution of the Dinosauriform Respiratory Apparatus: New Evidence from the Postcranial Axial Skeleton

Schachner, E. R., Farmer, C. G., McDonald, A. T., and P. Dodson. 2011. Evolution of the dinosauriform respiratory apparatus: new evidence from the postcranial axial skeleton. The Anatomical Record Early View. DOI: 10.1002/ar.21439

Abstract -
Examination of the thoracic rib and vertebral anatomy of extant archosaurs indicates a relationship between the postcranial axial skeleton and pulmonary anatomy. Lung ventilation in extant crocodilians is primarily achieved with a hepatic piston pump and costal rotation. The tubercula and capitula of the ribs lie on the horizontal plane, forming a smooth thoracic ‘‘ceiling’’ facilitating movement of the viscera. Although the parietal pleura is anchored to the dorsal thoracic wall, the dorsal visceral pleura exhibits a greater freedom of movement. The air sac system and lungs of birds are associated with bicapitate ribs with a ventrally positioned capitular articulation, generating a rigid and furrowed rib cage that minimizes dorsoventral changes in volume in the dorsal thorax. The thin walled bronchi are kept from collapsing by fusion of the lung to the thorax on all sides. Data from this study suggest a progression from a dorsally rigid, heterogeneously partitioned, multichambered lung in basal dinosauriform archosaurs towards the small entirely rigid avian-style lung that was likely present in saurischian dinosaurs, consistent with a constant volume cavum pulmonale, thin walled parabronchi, and distinct air sacs. There is no vertebral evidence for a crocodilian hepatic piston pump in any of the taxa reviewed. The evidence for both a rigid lung and unidirectional airflow in dinosauriformes raises the possibility that these animals had a highly efficient lung relative to other Mesozoic vertebrates, which may have contributed to their successful radiation during this time period.

8 comments:

  1. It's not really "new" evidence when it's exactly what Paul said in appendix 3 of DA...

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  2. And what Matt Wedel has been saying for many years before that.

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  3. Yeah, but she got out there, did the work and wrote the paper.

    :)

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  4. True, and that should never be undervalued.

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  5. Hardly seems fair to say Paul didn't "do the work and write the paper". DA isn't a peer reviewed journal, but it is a university press volume. Of course I haven't read Schachner et al. yet. Maybe they credit Paul?

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  6. Schachner et al.'s paper is much more extensive in scope and depth and a fair more detailed work in general, examining hard and soft tissues in extant birds and crocodilians and comparing those with the fossil dinosauriforms in between. She does cite "Dinosaurs of the Air", but realistically, this paper is the logical conclusion of work done by many others who have actually gone for in-depth studies of the pulmonary system of extant taxa (such as O'Connor, Claessens and Farmer).

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  7. Having now had a chance to look over the paper: yes, absolutely. It's good, detailed stuff.

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  8. Thanks for the copy of the paper, Nick. It does look good, and does cover sauropodomorphs and ornithischians in greater depth than DA. Schachner et al.'s earlier 2009 paper is a better match for DA since it's only about theropods.

    At least there they mention Paul in the paper, saying "Paul (2001, 2002) presented a generalized review of the anatomical characters of the theropod rib cage that supported the inference of an avian lung in Theropoda. We present additional evidence supporting this hypothesis by analyzing vertebral and rib morphology and positions of the articulation points between the ribs and vertebrae from individual theropod specimens with a well-preserved vertebral series. Our data indicate that rigid, dorsally anchored, nonexpansive lungs were present in Neotetanurae (sensu Sereno, 1999 and Avetheropoda of Paul, 1988 and Padian et al., 1999)."

    But really Schachner et al.'s ideas and figures are VERY similar to Paul's, and both have similar levels of detail (though on different aspects- Paul comments on more taxa and structures like sterna and pelves while Schachner goes into more detail about each specimen) and dependence on the literature. There's the osteological descriptions of lepidosaurs, crocs and birds, the figure comparing long- and short-sternumed birds, the discussion of theropod morphology in clades successively closer to birds, etc.. So if DA is a generalized review, so is Schachner's work. I know Paul can be a jerk, but it seems wrong to take basically the same data he presented (he was the first to refute and publish against Ruben et al.'s respiratory nonsense AFAIK), publish it years later as "new evidence" and give him a mere citation in one paper and a mention that makes his work sound less significant in another.

    I think it would have come off better if presented as "Paul (2002) described various osteological features that distinguish living reptiles with different respiratory systems and argued theropods had a bird-like system which was gradually acquired. Here we reiterate these features and describe the precise vertebral morphology of four avetheropods, confirming Paul's views."

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