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Re: tyranno growth



Greg Paul (GSP1954@aol.com) wrote:

<Took a look at the tyranno growth paper. The authors note that the body
mass estimates based on femoral circumferance are conservative. Indeed.
The value for Tyrannosaurus is just a little low, but those for the others
are low by a factor of two or more. Gorgosaurs, albertosaurs and
daspletosaurs were very large tyrannosaurs whose volume shows they massed
about 2.5 tonnes. No way they were only one fifth the size of
Tyrannosaurus, at the mass of wee cattle. An example of the perils of
using limb bone circumferance as indicators of mass, the relationship
between the two being highly inconsistent.> 
 
There are some problems inherent in using long bone scaling to estimate
mass, another means of doing so, as well as surface area projections (a
method endorsed by Christiansen at one point), and by Paul in making
models of animals to project body shape, and therefore mass from
volumetric displacement.

  These problems are:

  1. long bone scaling needs to know a living animal given's known mass,
and be compared to it. This was done by Christiansen (1999a, b), and
projected to dinosaurs by Christiansen (1999c). For dinosaurs, this value
is unknown, and the same work has not been done on birds or crocs to
calibrate such a practice. 

  Christiansen, P. 1999a. Scaling of the limb long bones to body mass in
  terrestrial mammals. _Journal of Morphology_ 239(2): 167-190.

  Christiansen, P. 1999b. Scaling of mammalian long bones: Small and large
  mammals compared. _Journal of Zoology, London_ 247(3): 333-348. 

  Christiansen, P. 1999c. Long bone scaling and limb posture in non-avian
  theropods: Evidence for differential allometry. _Journal of Vertebrate
  Paleontology_ 19(4): 666-680.

  2. Surface area projections are based on uncorroborated, rather
unscientific or unexplained methods of detailing rib volume or muscular
volume, tracheal volume, or shape and extent of the viscera, which are as
yet entirely hypothetical. No one has found a "live volume" for a dead
animal, especially those squished or flattened, despite traces of
integument _suggesting_ shape of the fur or scalation around the animal (a
product of taphonomic flattening).

<As for the nonsense about the speed slacking off at 1000 kg, Bill Sellers
and I will address that issue in joint presentations at SVP, including
advanced computer simulations. That giant tyrannosaurs were fast growing,
r-strategists that died young pretty much refutes the argument that they
dared not take the risk of dying from falling while running fast. They
lived an extreme, on the edge lifestyle.>

  We shall have to discuss the issue of speed _after_ SVP, when data is
actually offered, rather than before, unless the data will be offered
HERE. Otherwise, the statement "pretty much refutes the argument that they
dared not take the risk of dying from falling while running fast" makes
little sense in the logical arena: if an animal runs the risk of dying
when its running fast, would it not make sense that it did NOT do so? It
would be counter-productive that, during breeding age, you do something
that would impair either YOUR survival, or the survival of your species,
family, etc. This, along with muscular mass and effect in aiding movement
studies, implies rather than tyrannosaurs were SLOWER than some outre
workers would suggest, and that without much evidence to the contrary that
was not, in fact, also "explained away" by ancestry (i.e., earlier,
SMALLER tyrannosaurs had the arctometatarsus and the ornithomimid
proportions in legs, scaled up, because of common descent from animals
that made use of those for purpose of speed, as implied by Paul; however,
younger, derived forms with larger body mass retained these features and
used them in an exapted form as they were of use in their larger size, as
indicated in the snap-ligament studies (Holtz, 1994; Snively & Russell,
2002):

  Holtz, T.H., Jr. 1994. The arctometatarsalian pes, an unusual structure
  of the metatarsus of Cretaceous Theropoda (Dinosauria: Saurischia).
  _Journal of Vertebrate Paleontology_ 14(4): 480-519.

  Snively, E. & Russell, A.P. 2003. Kinematic model of tyrannosaurid
  (Dinosauria: Theropoda) arctometatarsus function. _Journal of
Morphology_
  255(2): 215-227.

  If you had, say, 5 years to propagate and ensure the survival of your
lineage, to the point of breeding, rearing, and ensuring your young are
healthy, you would not make a point of letting yourself die. Even in the
wild, animals tend to take less risky avenues when breeding or rearing, in
the sense to make sure their young are kept safe and fed; making secure
nest or brooding sites, foraging less openly, forming bond pairs to
protect young at all times, etc. If anyone has evidence to contradict this
in the general scheme of things, and can prove a "live fast, die young"
condition without a hypothetical scenario, but hard evidence, I would like
to see this.

  As an aside, "Sue," projected as the oldest known individual, appears to
have suffered from arthritic fusion in bones, had gout, and was of the
maximum mean size for known tyrannosaurs, suggesting that this animal was,
in fact, quite elderly for *Tyrannosaurus,* countering a possible "live
fast, die young" argument, unless this animal avoided the whole "risky
business" side of life and was a scavenger, thereby not really getting
involved in much confrontations, running out, etc.

=====
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 than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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