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Tiktaalik and basal tetrapod biomechanics



From: Ben Creisler
bcreisler@gmail.com

A new non-dinosaur paper that may be interest:

Bianca Hohn-Schulte, Holger Preuschoft, Ulrich Witzel & Claudia
Distler-Hoffmann (2013)
Biomechanics and functional preconditions for terrestrial lifestyle in
basal tetrapods, with special consideration of Tiktaalik roseae.
Historical Biology (advance online publication)
DOI:10.1080/08912963.2012.755677
http://www.tandfonline.com/doi/full/10.1080/08912963.2012.755677


The fossil Tiktaalik roseae from the Late Devonian induces clear
definition of the biomechanical and functional preconditions for a
terrestrial lifestyle including quadrupedal standing and locomotion on
limbs. Therefore, we determined the internal stresses in this model
organism under the influence of gravity using the finite element
method. Stress patterns during symmetrical two-forelimb support result
from bending of trunk and neck. During asymmetrical one-forelimb
support, as occurs during terrestrial locomotion, torsional stresses
are higher than those caused by bending. The observed patterns of
compressive stresses correspond well with the arrangement of
compression-resistant materials: vertebral column, shoulder girdle and
ribs. The tensile stresses are in accordance with the arrangement of
longitudinal and oblique muscles forming the body wall. Torsional
stresses concentrate along the periphery of the trunk, leaving its
cavity free from mechanical stresses. Theoretical mechanics indicate
that the flat skull and the mobility of the neck were advantageous for
lateral snapping, similar to crocodiles. The same movement on land
requires sprawling and flexed forelimbs. Our results can be
interpreted as explanations for the tetrapod bauplan as well as
confirmation and refinement of existing hypotheses about the lifestyle
at the border between water and land of this early predecessor of
terrestrial tetrapods.