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Re: My Gr. 9 Science Fair Project: Questions



>Well, okay.  Still, if a duckbill raced for the nearest water to escape
>a tyrannosaur, it seems unlikely that it would happen to step on a
>croc.  If the duckbill swam to get far from the tyrannosaur, could the
>croc close the distance before the croc's anaerobic energy ran out?

Unfortunately my Paleozoic tape measure got lost in the fossil record but,
as a hunch and knowing modern crocs, I'ld wager tender parts of my anatomy
on the croc taking a swimming hadrosaur with energy to spare.

>Large concentrations of duckbills nested in conspicuous colonies long
>enough for the young of one genus to hatch from 20-cm eggs and grow to
>at least a meter.  Wasn't that a strategy of protecting a few offspring
>rather than scattering many?  Even if duckbills were uncommon dinosaurs
>who fooled us by being especially good at leaving fossils, losses had to
>be controlled, and edmontosaurs lived in swamps.  (Should I trust what
>I've read?)

I'm not quite sure of you point here but even the best nesting strategies
of modern animals (many similar to those of hadrosaurs) still suffer from
juvenile and egg mortality due to predation. And, sure as Darwin determined
that little green apples evolved from non-fruit bearing ancestors, sooner
or later every hadrosaur would have to go near croc-infested water for a
drink. Once there, they would be fair game for those naughty little buggers
measuring up to 14 metres or more in length.

>The time I tried to shoot crows for my uncle, it was like the line from
>"Butch Cassidy": "Who ARE those guys?"

<snipping some boyhood recollections>

What is it with you and the bloody crows? Just because you can find an
example of a complex behavious in one group of animals does not mean that
you can invoke it to prop up your argument for another. Parsimony would
have us take a more sedate line in reconstructing hadrosaur-crocodile
interspecific activities: the closes analogue of that situation appears to
be herding mammal-crocodile interelationships occuring in modern Africa.
There the herding mammals, despite their numbers and communication
abilities etc etc, still fall prey to lurking crocs and the same is
probably likely for the hadrosaurs and crocs all those years ago. You could
draw analogies with a living group of you choice (ants, beavers or penguins
might make interesing analogies) but these would be harder to support.
Stone the bloody crows!

>Birds are used as models to speculate about dinosaurs.  If I were a
>croc, I'd hate to be hunting dinosaurs if they were as smart as crows.

OK, lets run with the birds. 25% of the diet of modern adult fresh water
crocodiles (Crocodylus johnstoni) are birds. Does this help with our
discussion?

>I think the question is not whether crocs ate edmontosaurs, but whether
>such incidents made it unfeasible for duckbills to enter the water.
>Occasionally somebody manages to shoot a crow, but it doesn't seem
>common enough to have much effect on the crow's long life expectancy,
>and they don't avoid cornfields.

I would have thought that shooting a crow would substancially alter its
life expectancy. Again, going back to a reasonable modern analog, modern
herding mammals will enter the water, in large groups, to drink or to cross
the water body. In these situations, they are vulnerable to and sucumb to
predation by crocodiles. Rarely, if ever, will the enter water to escape
predators because predators can follow them into the water and because they
risk the chance of being eatern by crocodiles. The level of predation by
crocs in these situations represents a significant pressure on the herd
dynamics of modern herding mammals. It is reasonable to assume that a
similar situation occurred for herding dinosaurs living with larger
crocodiles in the late Cretaceous.

Cheers, Paul


Dr Paul M.A. Willis
Consulting Vertebrate Palaeontologist
Quinkana Pty Ltd
pwillis@ozemail.com.au