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Fwd: possible role of echolocation in K-T survival

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In a message dated 98-03-10 01:28:25 EST, you write:

<< sn't echolocating similar in principle to sonar?  The medium is
 different, and the reception of sound is through different body parts
 (ears vs. melon), but isn't the principle of issuing sound to recieve
 sound wave bounces the same?
 
 Could ichthyosaurs have used sonar?
  >>


In principal, yes the system is the same.   A sound is emitted,
bounces off a target, and returns and is recorded.  The time lapse
computed against the known speed of sound (1100 fps in air but much
faster  in water, (I think approx 4800 if my memory serves correctly),
and distance is determined.  direction may also be determined
by the signal strength received from turning the receptors, or in the case of
an animal with two receptors, i.e. ears, by recording the difference in
returned strength and timing between the two receptors.

In general, as several others have pointed out, most echolocators live
in a low light environment, which leads to larger eyes if vision is important
to survival.  Echolocators also tend to pursue prey which can change
directions rapidly.  Bats chase insects, Sperm whales prey on giant squids.
Some bats, however, although nocturnal, eat fruit and do not echolocate or
presumably, have the ability to do so. 

As both bats and whales evolved after the K/T extinction, so the use
of these animals in this thread seems somewhat of an invalid example.

As for Icthyosaurs having the ability to echolocate?  I know of no predator
that eats fish that has this ability (this is not my area of study, so that
could be
off the mark).  Most fish eaters rely on speed, or surprise to overcome the
obstacles presented.  Large eyes in Icthyosaurs are based on a reasonably
large orbit, 
and the size of the sclerotic ring.  The animals actual visual acuity depends
on the size of the pupil opening, which remains undetermined. Humans as
children have a 7mm pupil, which degrades to around 5mm by age 35 or so.
Sharks,
on the other hand, have eyes that have a guanine layer behind the retina,
which reflects the light back, enabling the animal to use the same light
twice.
Some birds also use this feature (It escapes me exactly which species).
Owls, also a nocturnal hunter, locate prey mainly by sound, but have huge eyes
in relation to their body size, but alas, no echolocation here, just great
hearing.

In general, a broad look at the extant natural world reveals a wide variety of
eye/body ratios, combined with auditory capabilities.  I see no theoretical
block to Icthyosaurs having the Echolocating features, but I have also seen
no evidence to support it.

Bill Hinchman.

Absence of proof is not proof of absence.


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