Vertebrate paleo papers in July 22 Proceedings: Biological Sciences

[bh480@scn.org]

From: Ben Creisler bh480@scn.org
A number of vertebrate paleo papers (at least one 
mentioned here before in prepublication form) are in the 
new Proceedings: Biological Sciences:

Claessens, Leon P. A. M.,  2004. Archosaurian respiration 
and the pelvic girdle aspiration breathing of 
crocodyliforms. Proceedings: Biological Sciences 271 
(1547): 1461 - 1465 (July 22, 2004)
Abstract: 
Birds and crocodylians, the only living archosaurs, are 
generally believed to employ pelvic girdle movements as a 
component of their respiratory mechanism. This in turn 
provides a phylogenetic basis for inferring that extinct 
archosaurs, including dinosaurs, also used pelvic girdle 
breathing. I examined lung ventilation through 
cineradiography (high-speed X-ray filming) and observed 
that alligators indeed rotate the pubis to increase tidal 
volume, but did not observe pelvic girdle movement 
contributing to lung ventilation in guinea fowl, emus or 
tinamous, despite extensive soft-tissue motion. Re-
examination of fossil archosaurs reveals that pubic 
rotation evolved in basal crocodyliforms and that pelvic 
girdle breathing is not a general archosaurian mechanism. 
The appearance of pelvic aspiration in crocodyliforms is a 
striking example of the ability of amniotes to increase 
gas exchange or circumvent constraints on respiration 
through the evolution of novel accessory breathing 
mechanisms.

Rayfield, Emily J., 2004. Cranial mechanics and feeding in 
Tyrannosaurus rex. Proceedings: Biological Sciences 271 
(1547): 1451 - 1459 (July 22, 2004)

It has been suggested that the large theropod dinosaur 
Tyrannosaurus rex was capable of producing extremely 
powerful bite forces and resisting multi-directional 
loading generated during feeding. Contrary to this 
suggestion is the observation that the cranium is composed 
of often loosely articulated facial bones, although these 
bones may have performed a shock-absorption role. The 
structural analysis technique finite element analysis 
(FEA) is employed here to investigate the functional 
morphology and cranial mechanics of the T. rex skull. In 
particular, I test whether the skull is optimized for the 
resistance of large bi-directional feeding loads, whether 
mobile joints are adapted for the localized resistance of 
feeding-induced stress and strain, and whether mobile 
joints act to weaken or strengthen the skull overall. The 
results demonstrate that the cranium is equally adapted to 
resist biting or tearing forces and therefore 
the 'puncture-pull' feeding hypothesis is well supported. 
Finite-element-generated stress-strain patterns are 
consistent with T. rex cranial morphology: the maxilla-
jugal suture provides a tensile shock-absorbing function 
that reduces localized tension yet 'weakens' the skull 
overall. Furthermore, peak compressive and shear stresses 
localize in the nasals rather than the fronto-parietal 
region as seen in Allosaurus, offering a reason why 
robusticity is commonplace in tyrannosaurid nasals.

Cisneros, Juan C., Ross Damiani, Cesar Schultz, Átila da 
Rosa, Cibele Schwanke, Leopoldo W. Neto, Pedro L. P. 
Aurélio, 2004. A procolophonoid reptile with temporal 
fenestration from the Middle Triassic of Brazil. 
Proceedings: Biological Sciences 271 (1547): 1541 - 1546 
(July 22, 2004)
The small tetrapod Candelaria barbouri, from the Middle 
Triassic of southern Brazil, is the first example of an 
owenettid procolophonoid outside Africa and Madagascar. 
Candelaria barbouri was originally described as a 
primitive procolophonid; however, a re-examination of the 
holotype, as well as new material, reveals that C. 
barbouri is in fact the youngest member of the 
Owenettidae, extending the chronological range of the 
group by more than 10 million years. The recognition of C. 
barbouri as an owenettid points to a broader diversity and 
distribution for owenettids than hitherto thought. In 
addition, C. barbouri is the first member of the 
Owenettidae to exhibit temporal fenestrae, a discovery 
that draws attention to the significance of this feature 
in 'anapsid' reptiles.