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RE: Re : New Tyrannosaurus paper

Tracy L. Ford
P. O. Box 1171
Poway Ca  92074

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Jaime A. Headden
Sent: Saturday, March 02, 2002 11:45 PM
To: dinosaur@usc.edu
Cc: dexter1647@caramail.com
Subject: Re: Re : New Tyrannosaurus paper

Thomas Miller (dexter1647@caramail.com) wrote:

<First, I don't think we have any kind of idea how "thick" or "powefull"
theropod muscle really was. We may have some muscle impression on bones,
but only the ones in contact with the bones, and thus a very small
percentage and argueably not from the species here (?).>

  Of course, and all true. But one must also note that muscles of
particular size, mass, etc., also leave particular types or sizes of marks
on bones. The thigh, hip, shin, and ankle musculature studied by
Hutchinson and Garcia all leave specific correlates on the bones that
relate to other taxa and mass of these muscles can be calculated from the
size of the attachments. This is one manner in which muscle size can be
calculated, and the study is plausible by extension. So far, this is one
of the few studies that have tried to estimate _mass_ of muscle, rather
than position and effect, which Hutchnson himself has been doing for
years, as has Steve Gatesy before him, Romer and Coombs on other archosaur
hips, and a few other major studies. Russell did study on similar
ornithomimid hips, as well.<<
Yea, Romer wasn't listed in the bibliography. For those who want to know.
Gregory, W. K., 1919, The pelvis of Dinosaurs; a study of the relations
between Muscular stresses and skeletal forms: Copeia, n. 69, p. 18-20.
Gregory, W. K., and Camp C. L., 1918, Studies in comparative myology and
osteology. Part III: Bulletin of the American Museum of Natural History, v.
28, p. 447-563.

Romer, A. S., 1923, The pelvic musculature of Saurischian dinosaurs:
Bulletin of the American Museum of Natural History, v. 48, p. 605-617.
Romer, A. S., 1927, The pelvic musculature of orntihsichian dinosaurs: Acta
Zoologica, v. 8, p. 225-275.

Coombs of course was on ankylosaurs

Coombs, W. P. jr., 1979, Osteology and Myology of the hindlimb in the
Ankylosauria (Reptilia, Ornithischia): Journal of Paleontology, v. 53, n. 3,
p. 666-684.

<Second, as far as I know, theropod iliums are truly exagerated when
compaired to actuall animals. Only the smallest land animals have such
exagerated iliums (e.g Felis domesticus, at least). The also state that
poor runners have less than 5% of their mass in leg muscles and 10%+
equals good runners. Truth is, that is according to OUR standards, modern

  Actually, birds of all types have very, very large ilia. Many advanced
quadrupedal dinosaurs, like titanosaurs and ankylosaurs, have very large
ilia, but are still not considered swift runners.<<

Yes, but large in one isn't the same as large in another. The ilia are
shaped differently so you really can't compare them to each other that well.
Birds and theropods have different ilia in that they are large in different
ways, thus the muscle attachment isn't the same, even though the same
muscles are used. Pubis and ischia as well as the caudo-femoralis muscle. If
the femur was held the way Hutichinson & Gracia have it, how does the
caudo-femoralis fit? Wouldn't that be stretched really far? I liken it to
how different the wing muscles between pterosaurs and birds (well, maybe not
that drastic but you should get the idea).

<Was a 20-30% of mass even possible, say common 65 million years ago ?
Nobody really knowns.>

  It is in some birds well over 30%, and such osteological features that
indicate mass in these taxa indicate that similar values were present in
cursorial theropods, like *Tyrannosaurus*.

Ok, to play devils advocate, 70% isn't.

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making
leaps in the face of adversity, that a simple skip is so hard to do.  We
should all learn to walk soft, walk small, see the world around us rather th
an zoom by it.

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