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Re: Sad Songs Make Me Cry (Was Parasaurolophus Greastest Hits)



> On Wed, 17 Dec 1997, William Monteleone wrote:
> 
>  People have been making replicas of Parasaurolophus crests and
> trumpeting into them for a couple of years now. But has anyone stopped
> to think that we're still missing the soft tissues which made the sounds? 
>Garbage in Garbage out.
 
Missing soft tissue is indeed a problem but, at least in the case of 
Parasaurolophus, I believe that you have exaggerated the difficulty.  
Unless we assume that soft tissue blocked the passage leading from 
the nostrils up through the crest and down to the back of the mouth, 
the length of the air passage can be found with reasonable accuracy. 
(I acknowledge that the animal may have breathed only through its 
mouth but I doubt it.)

When we are talking about resonant frequencies, the most important 
factor to consider is the length of the air passage.  Changes in 
diameter along the passage due to soft tissue may cause the 
introduction of additional sets of harmonics but the lowest set of 
frequencies is determined by the overall length of the air passage.  
This probably explains why the computer simulation done in New Mexico 
sounds exactly like the pipe model of a parasaurolophus skull that I 
built as part of my school science fair project last year.

If we are talking about other crested hadrosaurs, the problem with 
missing soft tissue becomes more important.  This is what has led me 
to do a project this year on elephant vocalizations.  I was looking 
for a living analogue of a hadrosaur but I've already learned more 
than I was counting on.  Elephants are able to generate frequencies 
in the range of about 15 Hz -- lower than any frequency that I 
calculated last year for any hadrosaur.  To me this suggests that 
hadrosaur vocalizations may have been even lower in frequency because 
they were larger animals.  The focus of my current project is to 
determine a mechanism for infrasonic elephant vocalizations.  I am 
hoping that I will be able to apply any insights to the hadrosaur 
vocalizations.

It is already clear that at least some of the audible frequencies 
produced by elephants are due to resonance in an open or a doubly 
closed air column.  I have determined this by using sound analysis 
software to analyse recordings of elephant calls.  (My software is 
Cool Edit.)

At the moment, the most promising hypothesis to explain the 
infrasonic vocalizations seems to be that the elephant uses its lungs 
together with its trunk to form a Helmholtz resonator.  Failing this, 
I hope to look at the elephant as a bubble resonator.  These 
hypotheses are not original to me but are suggestions made by people 
on the Bioacoustics Mailing List.

Della Drury
drury@telusplanet.net