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Polar dinosaur growth and other new papers



From: Ben Creisler
bh480@scn.org

My old email has been offline for a few days so there are 
a few new papers to post.

Woodward, H.N., Rich, T.H., Chinsamy, A and Vickers-Rich, 
P. (2011)
Growth Dynamics of Australia's Polar Dinosaurs. 
PLoS ONE 6(8): e23339. 
Doi:10.1371/journal.pone.0023339
http://www.plosone.org/article/info%3Adoi%2F10.1371%
2Fjournal.pone.0023339

Analysis of bone microstructure in ornithopod and 
theropod dinosaurs from Victoria, Australia, documents 
ontogenetic changes, providing insight into the 
dinosaurs' successful habitation of Cretaceous Antarctic 
environments. Woven-fibered bone tissue in the smallest 
specimens indicates rapid growth rates during early 
ontogeny. Later ontogeny is marked by parallel-fibered 
tissue, suggesting reduced growth rates approaching 
skeletal maturity. Bone microstructure similarities 
between the ornithopods and theropods, including the 
presence of LAGs in each group, suggest there is no 
osteohistologic evidence supporting the hypothesis that 
polar theropods hibernated seasonally. Results instead 
suggest high-latitude dinosaurs had growth trajectories 
similar to their lower-latitude relatives and thus, rapid 
early ontogenetic growth and the cyclical suspensions of 
growth inherent in the theropod and ornithopod lineages 
enabled them to successfully exploit polar regions.
---

David C. Evans, Paul M. Barrett,  and Kevin L. Seymour 
(2011) 
Revised identification of a reported Iguanodon-grade 
ornithopod tooth from the Scollard Formation, Alberta, 
Canada.
Cretaceous Research (advance online publication)
doi:10.1016/j.cretres.2011.07.002
http://www.sciencedirect.com/science/article/pii/S01956671
11000978

Abstract
An isolated tooth from the late Maastrichtian strata of 
the Scollard Formation of Alberta, Canada, has been 
identified as the only record of a non-hadrosaurid 
hadrosauriform from the Maastrichtian of North America. 
Here, we demonstrate that this identification is in error 
and that the tooth pertains to an indeterminate 
ceratopsid. In addition, we provide full documentation of 
the published collection of Scollard Formation fossils 
from which the tooth was originally derived.

----
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 (advance online publication)
DOI: 10.1002/ar.21439
http://onlinelibrary.wiley.com/doi/10.1002/ar.21439/abstra
ct
 
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.

----

Brian M. Davis (2011)
Evolution of the Tribosphenic Molar Pattern in Early 
Mammals, with Comments on the ?Dual-Origin? Hypothesis. 
Journal of Mammalian Evolution  (advance online 
publication)
DOI: 10.1007/s10914-011-9168-8
http://www.springerlink.com/content/33n11u34336t5537/

Development of the tribosphenic molar was a fundamental 
event that likely influenced the rise of modern mammals. 
This multi-functional complex combined shearing and 
grinding in a single chewing stroke, and provided the 
base morphology for the later evolution of the myriad 
dental morphologies employed by mammals today. Here a 
series of morphotypes are presented that represent 
stepwise acquisition of characters of the molar crown, in 
an effort to clarify homologies and functional analogies 
among molars of tribosphenic and tribosphenic-like 
mammals, as well as their putative sister groups. This is 
accomplished by evaluation of wear features, which 
provide direct evidence of occlusal function, and mapping 
these features on molars of the various morphotypes 
demonstrates their utility in determining homology. The 
original singular lower molar talonid cusp is homologous 
with the hypoconid, and upper molar cusp C in early 
mammals is homologous with the metacone (cusp ?C? is a 
neomorph with variable occurrence). The lingual 
translation of the metacone to a position more directly 
distal to the paracone (as in Peramus) creates an 
embrasure for the lower molar hypoconid, and is 
accompanied by the development of the hypoconulid and a 
new shearing surface. Lastly, the Gondwanan radiation of 
tribosphenic-like mammals, the Australosphenida 
(including monotremes), is determined to be functionally 
non-tribosphenic. The Tribosphenida are restricted to 
Laurasian taxa, with an origin at or just prior to the 
Jurassic-Cretaceous boundary.