New Papers in Wonderland

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

A couple new things are out.  First, more on _T. rex_ being wholly unable to 
chase down a Jeep in fourth gear:

Hutchinson, J.R., Ng-Thow-Hing, V., and Anderson, F.C. 2007. A 3D 
interactive method for estimating body segmental parameters in animals: 
application to the turning and running performance of Tyrannosaurus rex. 
Journal of Theoretical Biology 246(4):660-680. doi: 
10.1016/j.jtbi.2007.01.023.

ABSTRACT: We developed a method based on interactive B-spline solids for 
estimating and visualizing biomechanically important parameters for animal 
body segments. Although the method is most useful for assessing the 
importance of unknowns in extinct animals, such as body contours, muscle 
bulk, or inertial parameters, it is also useful for non-invasive measurement 
of segmental dimensions in extant animals. Points measured directly from 
bodies or skeletons are digitized and visualized on a computer, and then a 
B-spline solid is fitted to enclose these points, allowing quantification of 
segment dimensions. The method is computationally fast enough so that 
software implementations can interactively deform the shape of body segments 
(by warping the solid) or adjust the shape quantitatively (e.g., expanding 
the solid boundary by some percentage or a specific distance beyond measured 
skeletal coordinates). As the shape changes, the resulting changes in 
segment mass, center of mass (CM), and moments of inertia can be recomputed 
immediately. Volumes of reduced or increased density can be embedded to 
represent lungs, bones, or other structures within the body. The method was 
validated by reconstructing an ostrich body from a fleshed and defleshed 
carcass and comparing the estimated dimensions to empirically measured 
values from the original carcass. We then used the method to calculate the 
segmental masses, centers of mass, and moments of inertia for an adult 
Tyrannosaurus rex, with measurements taken directly from a complete 
skeleton. We compare these results to other estimates, using the model to 
compute the sensitivities of unknown parameter values based upon 30 
different combinations of trunk, lung and air sac, and hindlimb dimensions. 
The conclusion that T. rex was not an exceptionally fast runner remains 
strongly supported by our models-the main area of ambiguity for estimating 
running ability seems to be estimating fascicle lengths, not body 
dimensions. Additionally, the craniad position of the CM in all of our 
models reinforces the notion that T. rex did not stand or move with 
extremely columnar, elephantine limbs. It required some flexion in the limbs 
to stand still, but how much flexion depends directly on where its CM is 
assumed to lie. Finally we used our model to test an unsolved problem in 
dinosaur biomechanics: how fast a huge biped like T. rex could turn. 
Depending on the assumptions, our whole body model integrated with a 
musculoskeletal model estimates that turning 45° on one leg could be 
achieved slowly, in about 1-2 s.


Then, at the risk of tooting my own horn:

Harris, J.D. 2007. The appendicular skeleton of Suuwassea emilieae 
(Sauropoda: Flagellicaudata) from the Upper Jurassic Morrison Formation of 
Montana (USA). Geobios. doi: 10.1016/j.geobios.2006.02.002.

ABSTRACT: Appendicular elements of the sauropod dinosaur Suuwassea emilieae, 
from the Upper Jurassic Morrison Formation of Montana, USA, display a 
peculiar mix of autapomorphic and plesiomorphic features. While more similar 
in overall morphology to Apatosaurus than other flagellicaudatans, the 
coracoid of Suuwassea lacks the quadrangular shape of Apatosaurus. The 
humerus of Suuwassea bears a pronounced proximal tuberculum, a feature seen 
elsewhere only in saltasaurine titanosaurian sauropods. The rectangular 
proximal articular surface of the tibia is proportioned neither like 
Diplodocus nor Apatosaurus type specimens, although this region may be 
intraspecifically variable. The pes of Suuwassea possesses plesiomorphically 
elongate phalanges and a small, uncompressed ungual, unlike other 
flagellicaudatans except Dyslocosaurus. The localization of tooth marks on 
the pedal elements suggests that sauropod feet may have been singled out by 
scavengers, as has been noted for elephants.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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)