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New dinosaur paper: Ankylosaur tail club smacking

Not a paper dinosaur. And can you really call an article in PLoS ONE a
"paper" if it is an online journal?


Arbour VM (2009) Estimating Impact Forces of Tail Club Strikes by
Ankylosaurid Dinosaurs. PLoS ONE 4(8): e6738.


It has been assumed that the unusual tail club of ankylosaurid dinosaurs was
used actively as a weapon, but the biological feasibility of this behaviour
has not been examined in detail. Ankylosaurid tail clubs are composed of
interlocking vertebrae, which form the handle, and large terminal
osteoderms, which form the knob.

Methodology/Principal Findings
Computed tomographic (CT) scans of several ankylosaurid tail clubs referred
to Dyoplosaurus and Euoplocephalus, combined with measurements of free
caudal vertebrae, provide information used to estimate the impact force of
tail clubs of various sizes. Ankylosaurid tails are modeled as a series of
segments for which mass, muscle cross-sectional area, torque, and angular
acceleration are calculated. Free caudal vertebrae segments had limited
vertical flexibility, but the tail could have swung through approximately
100° laterally. Muscle scars on the pelvis record the presence of a large M.
longissimus caudae, and ossified tendons alongside the handle represent M.
spinalis. CT scans showed that knob osteoderms were predominantly
cancellous, which would have lowered the rotational inertia of the tail club
and made it easier to wield as a weapon.

Large knobs could generate sufficient force to break bone during impacts,
but average and small knobs could not. Tail swinging behaviour is feasible
in ankylosaurids, but it remains unknown whether the tail was used for
interspecific defense, intraspecific combat, or both.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
Faculty Director, Science & Global Change Program, College Park Scholars
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA