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New work on running biomech by Hutchinson



Greetings,

I haven't seen these mentioned on the list yet:

Hutchinson, J.R. 2004. Biomechanical Modeling and Sensitivity Analysis of
Bipedal Running Ability. I. Extant Taxa. JOURNAL OF MORPHOLOGY 262:421?440
(2004).

Hutchinson, J.R. 2004. Biomechanical Modeling and Sensitivity Analysis of
Bipedal Running Ability. II. Extinct Taxa. JOURNAL OF MORPHOLOGY 262:441-461
(2004).

The first details work on living critters (Homo, Macropus, Basiliscus,
Iguana, Alligator, Eudromia, Gallus, Meleagris, Dromaius, Struthio),
including determining many varied input factors and variables for his
mathematical modelling. Modelling Alligator and Iguana as exclusively
bipedal shows that they would be lousy runners... It also corrects the giant
6 tonne chicken data from the Hutchison & Garcia (2002) paper, and shows
that in fact it should have a total muscle mass of 62% of its body mass as
limb extensors per leg, not 99% :-).  This paper goes into far more detail
about the mathematical modelling used than the previous short Nature paper.

The second paper is the one that this list is probably more interested in.
Here's the abstract:
Using an inverse dynamics biomechanical analysis that was previously
validated for extant bipeds, I calculated the minimum amount of actively
contracting hindlimb extensor muscle that would have been needed for rapid
bipedal running in several extinct dinosaur taxa. I analyzed models of nine
theropod dinosaurs (including birds) covering over five orders of magnitude
in size. My results uphold previous findings that large theropods such as
Tyrannosaurus could not run very quickly, whereas smaller theropods
(including some extinct birds) were adept runners. Furthermore, my results
strengthen the contention that many nonavian theropods, especially larger
individuals, used fairly upright limb orientations, which would have reduced
required muscular force, and hence muscle mass. Additional sensitivity
analysis of muscle fascicle lengths, moment arms, and limb orientation
supports these conclusions and points out directions for future research on
the musculoskeletal limits on running ability. Although ankle extensor
muscle support is shown to have been important for all taxa, the ability of
hip extensor muscles to support the body appears to be a crucial limit for
running capacity in larger taxa. I discuss what speeds were possible for
different theropod dinosaurs, and how running ability evolved in an inverse
relationship to body size in archosaurs. J. Morphol. 262:441-461, 2004. ©
2004 Wiley-Liss, Inc.

The taxa modelled are Coelophysis (AMNH 7224), Compsognathus (type),
Dilophosaurus (UCMP 37302), Allosaurus (MOR 693), Velociraptor (IGM
100/986), "small tyrannosaur" (an undescribed FMNH specimen), Tyrannosaurus
(MOR 555), Archaeopteryx (Berlin), Dinornis (UCMP 77209). Some the specimens
were run under a variety of postures (esp. the adult T. rex).  Based on
these models, the adult T. rex would not make a good "fast runner" (fast
running is defined in these papers as a Froude number of ~17, which scaled
to MOR 55 would mean 20 m/s). All the other specimens seem to have been
fairly good fast runners. Hutchinson still regards a speed of >11 m/s in the
full grown T. rex as rather unlikley, but between 5-11 m/s not out of the
realm of possibility but requiring further study. At Froude = 17, the
Coelophysis would be moving at 8-9 m/s, and the small tyrannosaur at 11-14
m/s (the current upper ranges of footprint-based speeds). The data also
suggest that Dinornis was a decent runner, rather than a slower mover (as
other moas probably were).  He again laments the lack of good data on the
locomotion (including top speeds) of large modern mammals.

Hutchinson willingly admits that "other approaches,such as a superior
biomechanical model,could contradict my biomechanical analysis by showing
that crucial,realistic new assumptions change the estimates of m-sub-i
enough to support the hypothesis that the largest theropods could run much
faster than 11 m/s." But that it isn't just enough to say that you don't
like the results: you've got to put your money where your mouth is (as they
used to say), and actually do the work.

[Incidentally, m-sub-i is the required muscle mass about joint i (expressed
as a % of the body mass)].

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796