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How giant amphibians put the bite on Triassic archosaurs



From: Ben Creisler
bcreisler@gmail.com

OK--not dinosaurs, but clearly early dinosaurs and other archosaurs
during the Triassic had nasty encounters with giant temnospondyl
amphibians.

Fortuny, J., Marcé-Nogué, J., Gil, L. and Galobart, À. (2012)
Skull Mechanics and the Evolutionary Patterns of the Otic Notch
Closure in Capitosaurs (Amphibia: Temnospondyli).
The Anatomical Record (advance online publication)
doi: 10.1002/ar.22486
http://onlinelibrary.wiley.com/doi/10.1002/ar.22486/abstract


Abstract
Capitosaurs were among the largest amphibians that have ever lived.
Their members displayed an amphibious lifestyle. We provide new
information on functional morphology data, using finite element
analysis (FEA) which has palaeoecological implications for the group.
Our analyses included 17 taxa using (2D) plate models to test four
loading cases (bilateral, unilateral and lateral bitings and skull
raising system simulation). Our results demonstrates that, when
feeding, capitosaurs concentrated the stress at the circumorbital
region of the capitosaur skull and cranial sutures probably played a
key role in dissipating and absorbing the stress generated during
biting. Basal members (as Wetlugasaurus) were probably less
specialized forms, while during Middle- and Late Triassic the group
radiated into different ecomorphotypes with closed otic notch forms
(as Cyclotosaurus) resulting in the strongest skulls during biting.
Previous interpretations discussed a trend from an open to closed otic
notch associated with lateral repositioning of the tabular horns, but
the analysis of the skull-raising system reveals that taxa exhibiting
posteriorly directed tabular horns display similar results during
skull raising to those of closed otic notch taxa. Our results suggest
that various constraints besides otic notch morphology, such as the
elongation of the tabular horns, snout length, skull width and
position, and size of the orbits affect the function of the skull. On
the light of our results, capitosaur skull showed a trend to reduce
the stresses and deformation during biting. Capitosaurs could be
considered crocodilian analogues as they were top-level predators in
fluvial and brackish Triassic ecosystems.