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Upper size limits in dinosaurs and whales



I wonder if anyone out there can help me.  I am putting the final touches on 
a children's question-and-answer book on nature, which has involved me 
checking some text I wrote over a year ago, and (with a publisher's deadline 
breathing down my neck) I find I have written myself into a bit of a corner.

The question I posed was, simply, "How can whales grow so large?"  and my 
answer was that the buoyancy of water permits a much larger body size than 
would be possible on land.  I even said that a hundred-ton animal on land my 
be crushed by its own weight.

Well, of course, along comes David Gillette's book on Seismosaurus, with 
estimates in the hundred-ton range for both Seismosaurus  and Ultrasaurus.  
So much for my point.

What I would like to know, though, is: are these weight estimates generally 
accepted?  Has anyone analysed the mechanics of such a beast?  And is the 
reason a large whale dies on the beach independent of size (as it might be 
because even dolphins die during strandings, I suppose).

Anyway, I would appreciate any guidance on this.  Here is my original text:

----------

How can whales grow so large?

Water can support the weight of even the largest whale.  On land, a 
hundred-ton animal might be crushed by its own weight.

On land, very big animals have a problem - gravity.  Even the largest 
dinosaurs were much lighter than a blue whale [WELL, I GUESS THAT ISN'T 
TRUE!]  In the ocean, whales don't have that problem because water buoys 
them up.  They still need vast amounts of food to supply their huge bodies, 
but their size helps them retain heat in icy waters.

A whale stranded on a beach, though, is in trouble even though it can 
breathe air.  It may overheat in the sun, and the weight of its body can 
crush its internal organs.  many people try to help stranded whales, but it 
is very difficult to do this properly.

------------

Any comments, flames etc would help.  Might food be a greater limiting 
factor than gravity, so that the filter-feeding methods of large whales (not 
available to sauropods) may have permitted (or even required) large size?
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
Home: 1825 Shady Creek Court                  Messages: (416) 368-4661
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Toronto, Ontario Canada M5H 3P5