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"Cursoriality", etc.



Well, looks like I get to play the heretic today. A few comments--

1) Speed is a product of stride length and _stride frequency_, not stride
length alone. A lot of discussions on theropod locomotion have focused on
the stride length issue. This is understandable, since the stride frequency
end is tough to tackle. But please don't forget it.

2) Please read Gatesy and Middleton's 1997 paper (JVP 17:308-329). Then
read it again. Two quotes from page 316: "Hummingbirds, alcids,
kingfishers, and penguins share [high] T/F ratios with ostriches, but would
never be considered cursors. This alone should warn of the absurdity of
assessing running ability from just these two measures." and
"Unfortunately, non-bird theropod tarsometatarsi have a very small range
[of proportions].... This is within the range of variation among [extant
ratites]."

3) I took a few minutes and looked through a few papers and books on
scaling, such as Peters' _The ecological implications of body size_, and
Calder's _Size, Function, and Life History_. Gee, with increasing body
mass, the following parameters (in extant taxa) decrease: stride frequency,
limb joint angles; and increase: limb length, duty factor, trot-gallop
transition speed. And if you've followed any work by Andrew Biewener in the
last 15 years, you'll know that large animals assume more straight-legged
postures relative to smaller ones. I'm not saying anything directly about
tyrannosaurs, but I don't think the evidence from living animals is
dismissable a priori. I've even read in a fairly recent dinosaur paleo
paper something like "no scaling studies have shown that large animals
cannot move quickly." Whatever...

4) I refer you to Ted Garland's 1983 paper "The relation between maximal
running speed and body mass in terrestrial mammals." J Zool Lond 199:
157-170. Does the curve in the main graph of speed/mass go straight up
exponentially, or is it more parabolic? In case you don't have it handy, it
corroborates what Hildebrand, Gray, Coombs, etc. had already suspected:
that somewhere around 100kg, gravity begins to take its toll on locomotory
ability. Also see a followup by Garland & Janis in J Zool Lond 229:133-151,
"Does metatarsal/femur ratio predict maximal running speed in cursorial
mammals?" Abstract, last sentence: "Prediction of locomotor performance of
extinct forms, based solely on their limb proportions, should be undertaken
with caution." And have we read our daily dose of George Lauder today? :-)

5) Biomechanists today, or at least since the late great C.Richard Taylor,
Fedak, Alexander, and a multitude of others stepped onto the scene in the
1970s, don't use the functional anatomist's kinematic definition of running
(suspended phase) anymore. For examples, see "Groucho running" (1987) by
McMahon et al. in J.Appl. Physiol. 62(6): 2326-2337, or "Vertical movements
in walking and running" (1978) by Alexander and Jayes in J.Zool Lond 185:
27-40, or "The spring-mass model for running and hopping" (1989) by
Blickhan in J. Biomechanics 22: 1217-1227, and references therein. The
dominant paradigm today is to model a walk with an inverted pendulum model;
a run or trot with a mass-spring model. There are animals that run without
a suspended phase. Lots of em, creeping and crawling around under our
noses. Their common mechanism of locomotion, shared with us and presumably
dinosaurs, can be modeled as an inverted pendulum or spring-mass.

6) I'll stop here lest I write my doctoral thesis via e-mail. :)

                        John R. Hutchinson
                 Department of Integrative Biology
                  3060 Valley Life Sciences Bldg.
                University of California - Berkeley
                     Berkeley, CA 94720 - 3140
                      Phone:  (510) 643-2109
                      Fax:    (510) 642-1822
         http://ucmp1.berkeley.edu/people/jrh/homepage.html