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brief replies



Hi again,
  Just a few comments to catch up on things I haven't replied to yet.  I
may not be able to reply to too many e-mails this week as I am off in
NYC doing research (3D laser-scanning Velociraptor legs for more
musculoskeletal models!).  As has become habit, Tom Holtz (with John
Merck and an entourage of students and teachers) and I just ran into
each other last night at the hotel through freak circumstance; 2nd time
in recent memory.  Small world!

Anyway, there isn't too much for me to reply to (phew, life has quieted
down at last!), but Tracy and Mickey mentioned that our Fig 1 is of
Daspletosaurus/Gorgosaurus. We did not assign the drawing to a genus,
and for our purposes it did not matter what genus was used. As you
probably realize, the illustration (which is properly credited, not
"ripped off") is from PDoTW and was just used as background to show the
whole body rather than just a boring stick figure.  We used the joint
angles from that drawing because it is one of the only reconstructions
of a tyrannosaur hindlimb in midstance that we could find. It is odd
that most artists show one limb (usually right) in late stance and the
other in late swing phase.  We tried some 30 different limb
orientations, only a few of which are shown in the Nature paper (see
simple 2D models in supp info gif image... they are ugly but they are
the real models and may show why we added extra art to figs 1+2).  It
didn't matter too much for our T estimates unless we used fairly
columnar limb orientations that put the trunk CM very close to the knee
joint.

As for other things, one issue to keep in mind is the interpretation of
so-called "cursorial" anatomical features.  My feeling, which I think is
the same as some other folks such as Carrano (see his "what, if
anything, is cursoriality" paper... sorry if I botched the title), is
that running and cursoriality have too long been assumed to be the same
thing.  I prefer to decouple the two issues.  "Cursorial" features are
generally anatomical specializations related to parasagittal
locomotion.  They are features that would be of use to any animal used
to moving around a lot, regardless of gait or speed.  Hingelike joints,
long legs, big muscles with proportional moment arms, distal muscle
attachments, etc. are all useful for any form of steady state
locomotion.

My opinion is that it has become untested dogma to assume that these
features evolved specifically for, and were maintained for, high speed
running only. The burden of proof is on people to demonstrate that these
features are useless or unimportant for fast walking or slow running.
They probably are also energy-saving mechanisms that are important for
animals that are on the move a lot.  We need to take a more scientific
look at cursoriality rather than make assumptions without ruling out
alternative hypotheses.  And I think that process of ruling them out
will be very hard.  Computer modeling and more work with living animals
are two approaches that might be productive.

Finally, thanks a lot to Luis Rey for the great tyrannosaur-chicken
painting, which has been shown on a lot of websites and news programs
(really great plug on NPR from the host!).  It was a real pleasure to
work with Luis!  I recommend to other scientists that he (and other
illustrators too I'm sure; I've only worked with Luis so far) is a kind
and reliable collaborator.  As you may have guessed, the painting was
done as a potential cover piece for Nature, but we found out that they
don't like humor as much as Science mag does (long story there).

OK enough for now, thanks for putting up with me.  :)

--John (no need for formalities like Dr or HP Hutchinson unless you
must; I am not keen on honorifics)