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Brooding Tyrannosaur (was Tyrannosaur Arm Capabilities)



> From: TomHopp@aol.com
>     Why did you start by rejecting the notion that it (_T.rex_)
"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 parsimony of this scenario depends on several debatable points.

Numero uno: Is _T.rex_ phylogenetically equally close to known "breasting"
avian and non-avian dinosaur genera as _Oviraptor_ (a presumed breaster)? 
Given the current state of resolution in the fossil record on the
"breasting" issue, and the degree of uncertainty regarding theropod
phylogeny in general, I would question which side of the argument (if any)
is deserving of the high "moral" ground on tyrannosaurid "breasting"
behavior, if phylogenetic bracketing is to be put forth as the best
evidence.

Numero two-o: As Jaime A. Headden points out, it would appear reckless for
tyrannosaurids to utilize a nesting strategy that routinely places the
weight of the massive parent down upon the diminutive eggs, or even in very
close proximity.  Small forelimbs notwithstanding, I think that the simple
physics of the situation would preclude safety in that this large animal
would be required to operate its large frame and major muscles under
excruciatingly close tolerances to avoid the "Humpty Dumpty" syndrome from
occurring (smashing the eggs).  Perhaps we should wait for future papers on
the nests of large theropods before we apply the presumed _Oviraptor_ and
_Troodon_ nesting behaviors to the large theropods.  Bear in mind that, for
all their vaunted maternal qualities, even the "good mother lizards" are
not presumed to be "nest breasters," and the duckbills seem to have gotten
by just fine with their well-documented tubercle scales (no feathers
required).  Despite the warmth of breasting dinosaur images, the tactic
would ill-suit the _Maiasaura_ intent on keeping its "good mother"
reputation.

>    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?

If we must pursue this further, we should think about what great advantage
the offspring would gain, when Jack Horner states that a large _T.rex_ arm
was about the same size as that of a grown man's arm, and it was buried up
to the elbow in chest muscle?  The remiges emanating from such a minimal
appendage would seem to me to be a poor excuse for continuously threatening
the eggs with imminent crushing from the barrel chest.  The poor mom would
be a nervous wreck!

Then, of course, we come to the problems of evidence.  There have been only
a few scant impressions identified with _Tyrannosaurus rex_, reportedly in
the playing card range, but these indicate tiny tubercles.  The only really
good skin impressions known for any large theropods are those associated
with _Carnotaurus_, and these are extensive and decidedly unfeathered. 
Could have been moulting, I suppose, but the texture does not give any
indication of foramina or follicles which would support such a hypothesis,
nor has there been any such indication for any of the two dozen large
dinosaurs' skin impressions extant.  Admittedly, the _Carnotaurus_ is less
bird-like than a tyrannosaurid, but what I am suggesting is that this is
one of those cases where "Size matters."  I am inclined to agree with
Norell that it would not be metabolically cost-effective for a dinosaur the
size of _T. rex_ to be heavily insulated, nor am I yet convinced that the
"breasting" or "brooding" strategies would be such a good idea for an
animal the size of _Tyrannosaurus rex_.  You could propose that
tyrannosaurids became sexually mature and produced clutches while still the
size of an ostrich or even an elephant bird, and later lost their
feathers...

I say stick with _Oviraptor_.  It's so funny looking, I wouldn't put
anything past it! 

-- Ralph Miller III     gbabcock@best.com

"Mother, don't smother."