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My Gr. 9 Science Fair Project: Questions



I have found the following book in the my school library: "Crocodiles and
Alligators" edited by Charles A. Ross; Facts On File Inc.(New York).

On page 107, I found the following: "Another type of acoustic message barely
perceptible to humans is the subaudible vibration, sometimes referred to as
infrasound, produced by many crocodillians.  The trunk muscles are rapidly
contracted just below the surface of the water, radiating wave pulses out
from the body, and the shallow water across the back bubbles up and bounces
off the back.  These extremely low frequency signals (1 - 10 hertz) are
close to the limits of human hearing but at close range resemble the sound
of distant thunder."

1)  The book does not explain the precise way in which the crocodilians are
able to hear these sounds.

        a)  Are the sounds detected normally by the ears?  I know that the
ears are closed  when the animal is under water but this should not stop
hearing.  This would mean that the ear detects the sound by conduction in
air and I have another argument against the second part of my hypothesis.

        b)  Are the sounds detected by bone conduction?  This would mean
that I have found an interesting fact but I have no help with an argument
for or against my hypothesis.


2)  My understanding is that crocodillians were predators on hadrosaurs.
I've now read in several places that hadrosaurs are thought to have escaped
from theropods by running into water.  This seems odd to me.  It seems a bit
strange to run away from one predator by running to another.  Can anyone
clear this up for me?

Thanks,
Della Drury