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Re: My Gr. 9 Science Fair Project: Questions



From: stevet@shelby.net (Stephen Throop)
 >
 > Could _T rex_ swim well?  Here's Robert Bakker: "But dinosaurs didn't
 > produce any swimming predators at all."

Well? I am not sure, but I would be surprised if they were totally
incapable of swimming. Few land vertebrates cannot swim at all.
Furthermore theropods are very similar to birds, many of which
swim habitually.  And the only reason I can think of why a crow
or sparrow would be unable to swim would be if their feathers got
waterlogged.

 >
 > If Cretaceous continents had a lot of broad, shallow waterways, why
 > didn't theropods produce swimming hunters?

Competition?
Insufficient aquatic prey?

 >
 > Suppose a giant croc was in ambush at the water's edge when he heard a
 > three-ton duckbill running toward him.  Wouldn't discretion be the
 > better part of valor?  After all, a croc killed by accident would still
 > be dead.

Water's edge isn't the main ambush location for crocs.  That is where
they *rest*.  Croc's ambush by floating just under the surface, out
of easy sight, and wait for prey to come close.  Then they lunge and
grab the prey quickly.
 >
 > In movies, crocs swim long distances toward human swimmers.  Is that
 > accurate?  GS Paul said, "Reptiles cannot aerobically sustain speeds
 > over 1-2 km/h no matter how toasty warm they may be."

The key word here is *sustain*.  A croc can easily *reach* quite
fast speeds, either on land (in their rarely seem erect stance)
or in the water, swimming.  An ambush huunter need not sustain
high speed, merely achieve it long enough to grab the prey.

 >  If they're that
 > slow on land,

They're not necessarily that slow.  A charging croc can be quite
fast - and terrifying.  They just cannot *keep* *going* at such
speeds.

 > it sounds as if a croc in the water would be pretty slow
 > once its anaerobic energy ran out.
 >
 > I don't know how many seconds or minutes this stored energy might
 > last.

Long enough for catching prey right next to them, which is how crocs
normally hunt terrestrial prey.  I have seen film of ?Nile crocodiles
suddenly appearing out of the water and grabbing quite substantial
prey - prey that could normally easily outrun them.

 > At least some duckbill genera inhabited conspicuous nesting grounds as
 > their young grew.  These were apparently not in swamps, but doesn't this
 > imply that they had methods of standing their ground against predators?

No, all it means is that they used predator overload to *avoid*
predators.  This works because predators get satiated, and there
are only so many of them.  This is why many birds today use mass
nesting.

 >
 > If duckbills were as smart as crows, I think they'd be familiar with the
 > haunts and habits of local crocs, be vigilant, and pass warnings.

That is likely as well.
 >
 > Don't crows drive hawks and owls from an area by harassment?

Yep, but crows are unusually pugnacious.  They are also more predatory
than most people realize.  In short, this is at least partially a
matter of chasing a potential *competitor* away.

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

The peace of God be with you.