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"Dinosaur Tectonics" in Journal of Geology


Dinosaur Tectonics: A Structural Analysis of Theropod Undertracks with
a Reconstruction of Theropod Walking Dynamics
Ole Graversen, Jesper Milàn, and David B. Loope1
Geology Section, Department of Geography and Geology, University of
Copenhagen, Geocenter Copenhagen, Øster Voldgade 10, DK-1350
Copenhagen K, Denmark
(e-mail: oleg@geol.ku.dk)

Manuscript received December 29, 2006; accepted June 4, 2007.

A dinosaur trackway in the Middle Jurassic eolian Entrada Sandstone of
southern Utah, U.S.A., exposes three undertracks that we have modeled
as isolated tectonic regimes showing the development of fold-thrust
ramp systems induced by the dinosaur's feet. The faulted and folded
sequence is comparable to crustal-scale tectonics associated with
plate tectonics and foreland fold-thrust belts. A structural analysis
of the dinosaur tracks shows the timing and direction of the forces
exercised on the substrate by the animal's foot during the stride.
Based on the structural analysis, we establish a scenario for foot
movements and weight distribution in the feet. During the end of the
weight-bearing phase of the stride, the weight of the animal was
transferred to the front of the digits, creating a rotated disk below
the foot that was bounded by an extensional fault at the front and a
thrust ramp toward the back. As the body accelerated, the foot was
forced backward. The rotated disk was forced backward along a
detachment fault that was bounded by lateral ramps. The interramp
segment matches the width of the dinosaur's foot, which created an
imbricate fan thrust system that extended to the far end of the
undertrack. The total length of the tectonic disturbance created by
the dinosaur is up to three times that of the original footprint.
Early, near-surface cementation gave the substrate the rheological
properties necessary for development of the observed structures.

     1 Department of Geosciences, University of Nebraska, Lincoln,
Nebraska 68588-0340, U.S.A.


Michael D. Barton
     Bozeman, MT
          MSU Bozeman, History-SETS Major