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Fwd: RE: Speed in giants and cursors



Hi all, some pertinent comments from Per Christiansen, forwarded by 
request.


----- Forwarded message from "Christiansen, Per" 
<P2Christiansen@zmuc.ku.dk> -----
From: "Christiansen, Per" <P2Christiansen@zmuc.ku.dk>
To: "'jrhutch@stanford.edu'" <jrhutch@Stanford.EDU>
Subject: RE: Speed in giants and cursors
Date: Thu, 7 Mar 2002 10:29:15 +0100

Dear All (John, you may forward this if you please).

I've been sent a number of correspondances as to the latest paper on 
limb
muscles and running ability in Tyrannosaurus, but I'll let the rest of 
you
duke it out as to the particulars.

To the study I will say this, however. It's foundation is solid and the
authors did make a good case in that they tried to alter the input data 
to
see how this affected things. I do believe, as I have written earlier, 
that
big theropods had more erect limbs than smaller species. This appears 
to be
a near universal adaptation among extant parasagittals to reducing 
bending
moments in the diaphyses and would be very improtant for big striding
two-leggers as well, running or not. This would, as the authors stated,
affect the study, due to different vector mechanics (and hence muscle
masses).

I have previously stated my case as to limb ratios, bone strengths, 
degree
of "cursoriality" and possible speeds in theropods, large and small, 
incl.
Tyrannosaurs. I still maintain that the limbs of giant theropods were 
not
strong enough to attain a suspended phase, but that people are way off 
if
they think (as some apparently did) that this implies big theropods were
slow. The enormously long limbs (very different from any extant mammal 
of
large stature) begs the question as to why theropods did not evolve 
shorter
and, thus, stronger limb bones with size (so imporatnt in mammals save 
one,
elephants), but maintained the (compared to body length) extremely long
limbs of smaller forms. Such limbs would have made possible very long
strides, and thus, fast locomotion (kmh-1), with or without the 
inclusion of
a suspended phase. Or, as I put it back then (tounge in cheek), if you 
going
to outrun a tyrannosaur, better do it from horseback. Otherwise you 
WILL NOT
MAKE IT!

As for extant animals there are a few things that must be borne in 
mind. No
study so far has addressed the various limb ratios to speed that are so
often claimed (by me too!) to be indicative of a given locomotor 
performance
in dinosaurs. The studies that have been made have either addressed 
only one
of these (usually m/f) or not taken into account the phylogenetic 
signal. If
such studies are to have any merit one must decouple this signal ("are
antelopes fast because they are long limbed or are they longlimbed 
because
they are fast" - apo vs plesiomorphy). Other studies have messed up the 
data
by including everything from small, bipedal saltators to giant, 
apomorphic
amblers, of course in order to expand the data base. But this only 
leads to
errors of interpretation (as has subsequently been shown several times).

Also, the entire basis for postulating a significant relationship 
between
limb ratios and speeds center around muscle vector mechanics (in vs
outlevers and speeds around joints), stride lengths and energy 
efficiency.
Thus, it might be expected that a significantly greater number of limb
ratios, ususally not addressed at all in such comparisons, that the 
usual
few will emerge as significant. And what's more, if one hindlimb ratio
emerges as significant, and another does too, how about combining both 
of
them. And fore+hindlimbs? The alternative would imply that forelimb
parameters were uncoupled from hindlimb parameters in the evolutionary
history of the same animal!

Detailed studies of speeds in extant animals have consistently shown 
that
many extant ungulates are very fastmoving, film analyses report speeds 
of
over 100 kmh-1 for some gazelles. Alexander et als study from 1977 shows
animals running "reasonably fast" (their words), but the authors 
explicitly
stated that the included animals could well have been faster. Most 
published
speeds are not particularly unreliable, certainly not exaggerations by
dozens of kmh-s. Just think about it. If Alexander et al were correct 
how
could an impala or gazelle possibly co-exist with the Cheetah, since 
they
are capable of only 50 kmh-1 and the Cheetah is more than twice as 
fast!! We
know from numerous studies that the Cheetah mainly preys on gazelles and
impalas. Many previous speed values are not nearly as unreliable as 
often
proclaimed. How can one claim that wild horse species are capable of 
merely
45-50 kmh-1 when one example is known of one animal running nearly 30 
kmh at
an average velocity of 48 kmh-1? The list goes on and on.

To this day we simply do not have any study whatsoever that provides us 
with
nearly enough information to extrapolate (with confidence) to animals as
different as theropod dinosaurs (although highly similar evolutionary
adaptations can easily be defended, due to the influence of gravity). 
And
that's why I send out this little "bulletin". Because such a study is in
press at the moment, by yours truly. I normally don't say anything about
projects until they're out, but in this case it might be relevant to 
note
that:

1) Most previous values of speeds in many terrestrial mammals appear to 
be
fairly accurate, and cannot be claimed to be biased exaggerations to the
level of dozens of kmh-1. This is also corroborated by the fact that 10
specimens within the same species will show 10 different top speeds. And
what's a top speed? It depends not only on anatomical adaptations but is
highly dependent on motivation. Ungulates probably never get anywhere 
near
their potential peak velocity without being chased by a predator.

2) Many limb ratios other than just m/f show a significant relationship 
with
peak velocity. Uncoupling the phylogenetic signal unanimously lowers the
correlations, albeit usually not significantly so. Thus, many limb 
ratios
can actually provide a reasonable guess as to whether or not the animal 
in
queation was a fast mover or not (no, I will not say which!)

3) Multivariate analyses on several parameters often lead to parameter
redundancy (unavoidable in a biological sample), but also to 
significantly
greater correlations with speed. Analyses of thousands of equations (and
checks for redundancy, eigen value correlation etc) indicate that the 
best
correlations can be obtained by multivariate studies of just 2 
parameters.
Addition of more causes redundancy and only modest, if any, increases in
correlation.

4) Even the best correlations are not impressive. Limbs of fast running
mammals are clearly designed for much more than just running fast. 
Probably
the energy minimization of long distance travel is very important in
evolution of limbs traditionally explained as "cursorial". Peak 
locomotor
speed comes a far cry from explaining limb morphology in extant,
parasagittal mammals.

And that's it. There's hope ahead. I'll expand studies of this database
later on, but the preliminary results are likely to provide us with a 
much
better foundation for assessing which limb ratios indicate fast 
locomotion,
and just how reliable they really are (limb lengths are not very good). 
How
does it realte to big theropods? Well, in my poinion they still fall 
well
within not just running, but decidedly FAST running mammals. Whether or 
not
this proves anything (or is merely highly suggestive) will await further
study.

Cheers
Per Christiansen












----- End forwarded message -----