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Re: Tyrannosaur Arm Capabilities



Tom Hopp wrote:

<Why did you start by rejecting the notion that it "breasted" the
nest? Its cousins oviraptor and Cock Robin both do/did this. You moved
away from, dare I say it? - parsimony, with that assumption.>

  The weight of the tyrannosaur's chest probaly logged in at a ton and
a half, or just a ton. On a six-foot tall mound, with some hollow
little eggs in the center, not to mention a not entirely solid
internal structure, this would be like driving a car over a small,
honeycombed dirt mound, and either caving in every hollow place
inside, or making the mound slide its surfacestrate off, exposing that
honeycomb interior, and subsequently the eggs.

  If the mound were *Oviraptor* style, this would be even more
dangerous to the eggs, because there's less between the surface and
the eggs, and unless the rex were very tender, and I have no problem
imagining this, those eggs would be yolk-patties in no time flat.
Thinking now, I realize I should have shown why I discounted the
"breasting" idea. However, if the nest were built just so, perhaps as
a trench under the ground, and the rex' claws could do this quite
well, then stuffed with matter, eggs, and covered with dirt and
heat-trapping loam, then very probably, the animal may have "breasted"
the nest. Hmmm.

<The simpler assumption is that T rex built an oviraptor style nest,
then put its arms around it, like oviraptor did. This would bring the
birds' favorite incubator, the breast, into contact with the eggs.
Furthermore, it would align the arm feathers around the nest or
hatchlings, the way that oviraptor, Caudipteryx, Protarchaeopteryx and
modern birds could/can do. These wing feathers are indespensible for
offspring protection in modern eagles, gulls, ostriches and quail, so
why assume there was no use for them in T rex?>

  I didn't discount feathers, or arm protecting or "mantling" in
rexes, just the "bresting" behavior. Build a cassowary-style mound,
and the feathers are useless for this task until the chicks hatch.

<A crude calculation tells me that T rex's arm span was a bit larger
than oviraptors', so a nest of twenty or so ostrich-sized eggs could
be covered and incubated breast-foremost, in the good old fashioned
way.>

  True. The rex' arms, as I see them, and using the calculations and
estimations in _Complete T. rex_ (Horner and Lessem, 1995), the arms
are very limited going sideways, fore, or aft at the shoulder joint.
The elbow joint, as a result, was more mobile, but still could not
twist sideways, so I didn't even think of covering the nest
bird-style. A crocodile was more my analogy.

<Regarding two clawed hand used for nesting - yes, there are modern
birds that dig nest scrapes with their hands, feathers and all
(whether they use their newly re-popularized wing claws or not, I
don't know - see earlier posts on this list). It seems to me that
theropod clawed hands may well have had primary uses in nest scraping
and chick rearing. That certainly seems to be the case for oviraptor.>

  Indubitably. Just in rex, I don't think it was likely. But I had not
considered a more oviraptor-like nest, that is, closer the the ground,
and took the high mound style too much credit.

==
Jaime A. Headden

Qilong, the website, at:
http://members.tripod.com/~Qilong/qilong.html
---
All comments and criticisms are welcome!

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