Re: sauropod necks again

["Matthew Bonnan" <mbonnan@hotmail.com>]

On necks and multiple hearts ...

Yeah, I felt compelled to throw in my hat here.  The whole problem with that 
article is that there is no other vertebrate, let alone tetrapod, that has a 
series of hearts running up its carotid arteries.  While it is indeed a cool 
idea, the authors do not bother to explain how such multiple hearts would 
form, what embryonic tissue would give rise to such a unique structure, what 
the primitive condition would be, how the sympathetic trunk and the vagus 
nerve would develop the multiple branches necessary for its function, etc.

Unfortunately, this is all nice speculation with very little testability.  
If they could even point to a reptile, let alone an extant archosaur, that 
has a feature to its carotid arteries and heart that would "lend itself" to 
becoming these multiple hearts, then we might have somewhere to go.  As for 
now, I know of no examples.

I suspect the "solution" to the Barosaurus heart to brain problem was solved 
along less spectacular routes.  For instance, the MDs examined a giraffe's 
skin and blood vessel arrangement (to their credit) but did not report the 
difference in the size of the brains in a giraffe versus that of Barosaurus, 
whose endocast you can hold in the palm of your hand.  Perhaps a tiny brain 
needs little blood?  What if Barosaurus didn't rear?  Is the mammalian way 
of mating (i.e., rearing up) the only way to mate?

As for the heart beats per minute, Knut Schimdt-Nielsen in his 1984 book on 
Animal Size, reports the number of beats per minute in a blue whale at 
between 9-20, not 30-40 which I think falls in the range of elephants (70-80 
for a healthy Homo sapiens by comparison).  Then again, whales are aquatic, 
are deep diving, and do all sorts of weird things with their pulmonary 
systems.  Who says that large mammals are the ultimate yard-stick for what's 
possible unless you tack extra hearts onto your carotid artery?

The unfortunate thing is that while this article was apparently published in 
a small journal, it got into the 1992 issue of Discover magazine's top 
something-or-other scientific discoveries of the year! It's no wonder people 
think all we do is speculate and make up good stories for the next Jurassic 
Park film.

The point is, if you propose an extraordinary mechanism, you need 
extraordinary evidence.  In this case, even the ordinary evidence does not 
convince.

Matt Bonnan
Dept Biological Sciences
Northern Illinois University


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