Another New Paper

["Jerry D. Harris" <jharris@dixie.edu>]

...mayhaps the last of the year...?  Anyway, another in the growing list of 
2007 nee 2006 papers:

Moreno, K., Carrano, M.T., and Snyder, R. 2006. Morphological changes in 
pedal phalanges through ornithopod dinosaur evolution: a biomechanical 
approach. Journal of Morphology 268(1):50-63. doi: 10.1002/jmor.10498. 
ABSTRACT: The evolution of ornithopod dinosaurs provides a well-documented 
example of the transition from digitigrady to subunguligrady. During this 
transition, the ornithopod pes was drastically altered from the 
plesiomorphic dinosaurian morphology (four digits, claw-shaped unguals, 
strongly concavo-convex joints, phalanges longer than wide, excavated 
collateral ligament fossae, presence of sagittal ridge, and prominent 
processes for the attachment of tendons) to a more derived condition 
(tridactyly, modification of the unguals into hooves, phalanges wider and 
thinner than long, lack of collateral ligament fossae, loss of sagittal 
ridge and tendon attachment processes, relatively flattened articular 
surfaces). These changes are particularly noteworthy given the overall 
conservatism in pedal morphology seen across Dinosauria. But what are the 
functional consequences of these specific morphological transitions? To 
study them, we examine a wide range of pedal morphologies in four non-avian 
dinosaurs and two birds. Our analyses of the external morphology, 
two-dimensional models (using Finite Element Analysis), and internal bone 
structure demonstrate that this evolutionary shift was accompanied by a loss 
of digit mobility and flexibility. In addition, pedal posture was modified 
to better align the pes with the main direction of the ground reaction 
force, thus becoming well suited to support high loads. These conclusions 
can be applied to other, parallel evolutionary changes (in both dinosaurs 
and mammals) that involved similar transitions to a subunguligrade posture.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT  84770   USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and     dinogami@gmail.com
http://cactus.dixie.edu/jharris/

"Trying to estimate the divergence times
of fungal, algal or prokaryotic groups on
the basis of a partial reptilian fossil and
protein sequences from mice and humans
is like trying to decipher Demotic Egyptian with
the help of an odometer and the Oxford
English Dictionary."
              -- D. Graur & W. Martin (_Trends
                  in Genetics_ 20[2], 2004)