[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Fuel for another debate



Mike Bonham writes:
 >
 > swf@elsegundoca.ncr.com              sarima@netcom.com       wrote:
 > > *My* personal speculation is that the short arms allowed T. rex
 > > to restrain potentially dangerous prey more rigidly (shorter
 > > arms means less freedom of movement).  In particular, I suggest
 > > that T. rex was specialized to eat Triceratops, ...
 >
 > ...
 >
 > On the other hand, tyrannosaur arms didn't dwindle away to nothing,
 > and analysis of the joints, tendon attachment points, and estimated
 bone
 > strength shows that they were very strong for their size, and
 therefore
 > must have been useful, even essential, for something important to
 the
 > animals' way of life.

This is my basis for supposing they were used as prey anchors.
That combined with the fact that they were positioned at almost
exactly the height of the back of *both* Triceratops and
Edmontosaurus.

 > Even the `smaller' tyrannosaurids (Albertosaurus, Gorgosaurus are
 big
 > enough for me!) had similarly proportioned arms to T.rex, so I doubt
 > it's a specialization to fending off Triceratops horns/shields,
 unless
 > a whole range of mini-ceratops had exactly the same defense
 mechanisms
 > and proportions.

First, the earlier ceratipsians were not that much smaller than
Triceratops.  Pentaceratops was almost as large, or even larger.
And forms like Centrosaurus and Anchiceratops were quite large,
really. Thus, slightly smaller ceratopsians paired with slightly
smaller tyrannosaurs seems to preserve the same proportions,
more or less.

 > And anyway, wouldn't the more numerous, non-armoured
 > duckbills be a more attractive prey?

I suspect that T. rex ate both with fair frequency.

Also, wasn't the relative abundance of the two groups reversed
in prior epochs?  That is, didn't Centrosaurus and company
outnumber Corythosaurus and company?  [I am unsure of this,
but that is what I remember].
 >
 > One idea is that tyrannosaurs might have killed by tackling their
 prey
 > from behind, straddling and pinning the victim with its body while
 biting
 > its victim's neck and head (clean off!?).  Perhaps a pair of tiny
 > but strong arms could pin the prey under T.rex's body and keep it
 centred
 > while the killing bite was given.  Is that necessary and sufficient
 to
 > explain this aspect of their anatomy?

This is *exactly* the grip I was talking about!
You are just emphasizing a different aspect of its benefit,
its benefit in keeping the prey in place for killing.
 >
 > Don't forget `Deinocheirus' -- known only by its huge, razor-clawed
 > multi-dactyl hand and arm.  Is it likely to come from a T.rex -
 sized
 > dromeosaur?

No.  The best evidence right now is that it was a giant
ornithomimid.  This implies a very different feeding strategy,
and probably a very different food preference.

 > How did it get so big, using the grasping-hand architecture,
 > if T.rex could be more successful/numerous using the tiny-hand
 architecture?

But, even if it *were* a raptor, one lesson of evolution is that
there is often more than one equally effecive solution to a problem.
 >
 > How about another, possibly related question: why were tyrannosaurs'
 mouths
 > so huge and toothy?  ...
 > Why wouldn't tyrannosaurs have been able to kill using a smaller
 gape
 > and fewer teeth, and then bit off smaller chunks at their leisure?

Probably the differences in tooth and jaw mechanics made a
mammalian style killing bite impossible.  A slashing/cutting
bite is closer to what they were capable of.  Such needs to
be larger to effectively kill prey (As both Bakker and Greg
Paul have pointed out).

So, my idea is that instead of the slash and follow until
the prey drops strategy postulated by Bakker and Paul, I
would suggest grab, slash and *hold* until it drops.  This
seems much more reliable.
 >
 > Is the size of the jaw an indicator of some essential aspect of
 their
 > lifestyle?  Perhaps taken together, a big mouth and small arms are
 clues
 > to an important feature of their way of life.

Yep, no question about that.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.