From: prl@csis.dit.csiro.au (Peter Lamb)
Subject: Re: Back to "Bales' scales"
Organization: CSIRO Division of Information Technology
Date: Mon, 14 Sep 1992 04:32:03 GMT

prl@csis.dit.csiro.au (Peter Lamb) writes (PRL>):

bobb@tekig1.PEN.TEK.COM (Robert W Bales) writes (BB>>):

BB>>But if we rephrase the question as "Why don't organisms have characteristics
BB>>resembling a number of types of otherorganisms instead of just one?", the
BB>>answer is "they do."  Consider an organism
...
BB>>    that uses echo location,
PRL>	It doesn't. Please provide any evidence that makes you think it does.
PRL>	It _does_ have a very sensitive bill, and can locate prey without touch
PRL>	or sight, but the way it does this is not echolocation.
...

Bob, in his characteristic manner, has not given us any evidence why we might
postulate that a platypus uses echolocation. I can provide some weak evidence
for this. However, as I indicated, it is now known which sense allows the
platypus to find a tasty snack at the bottom of a muddy creek, at night,
with eyes, ears and nostrils firmly closed. Ears closed? Now _that's_ funny
in an animal that's supposed to be echolocating!

I mentioned that there was some weak evidence (more supposition, but
believable) that the platypus has some sort of echolocation sense (even
with its ears closed).

	"It has been suggested that water movements reflected from stationary
	 objects, or created by moving ones, may be sensed as they trigger off
	 [mechanoreceptors on] the bill." [1], p58.

The cortex map of a platypus [1] p59, has a huge area devoted to the
bill, and the bill is known to be very sensitive to touch. To call
this possibility "echo location", though, and allow the assumption to
be made that it's somehow like that of bats or dolphins is a pretty
doubtful business.

This possibility, however, doesn't even rate a mention in [2], since in
between times a mechanism has been found by which the platypus can
locate its prey; electroreceptors on its bill[2,3,4,5]. The first
experiments by Scheich et al.[3, summarised in 2] indicated the ability
to detect fields down to ~300uV/cm, and the ability to use the sense
locate a hidden field source. Fields of a strength which can be easily
detected by the platypus are associated with the tail movements of the
freshwater shrimp eaten by the platypus, and with the movement of other
platypus prey. [4] and [5] investigate the sense further.

Now, to forestall Bob's biological Lego argument for the existence
of the platypus, there _are_ other vertebrates with electrical sense organs.
However, the electroreceptors of the platypus are different in form from,
and part of a different portion of the nervous system from those in other
known species with this sense.

Interestingly, the playtpus shares this particular form of electroreception
with one other mammal. The echidna[6]. Funny, that. Fits in right where
it's expected.

PRL>Could you tell us what your theory of creation is, and how the platypus
PRL>fits it?

Well, I'll leave that in, just as a reminder to Bob, who's apt to forget to
respond to such requests.


Peter Lamb (prl@csis.dit.csiro.au)


[1] Grant, T. and D. Fanning, "The Platypus", 1984, New South Wales University
	Press, Sydney.
[2] Griffiths, M., "The Platypus", Scientific American, May 1988, pp 60-67.
[3] Scheich, H, G. Langner, C. Tideman, R Coles & A. Guppy,
	"Electrorecption in the platypus??", Nature, v319, pp401-2, 1986.
[4] Gregory, J, A. Iggo, A. McIntyre, & P. Proske,
	"Receptors on the bill of the platypus", J Physiol, v400,
	pp512-538, 1988
[5] Gregory, J, A. Iggo, A. McIntyre, & P. Proske,
	"Responses of electroreceptors in the platypus bill to steady and
	 alternating currents", v409, pp391-404, 1989
[6] Gregory, J, A. Iggo, A. McIntyre, & P. Proske,
	"Responses of electroreceptors in the shout of the echidna",
	J Physiol, v414, pp521-538, 1989
-- 
Peter Lamb (prl@csis.dit.csiro.au)