From: rowe@pender.ee.upenn.edu (Mickey Rowe)
Newsgroups: talk.origins,sci.skeptic
Subject: Re: Coelacanth and change (was: "Re: Cro-Magnon: evidence for DEvolution?")
Date: 13 Aug 92 18:49:47 GMT
Followup-To: talk.origins
Organization: University of Pennsylvania

Note followups to talk.origins.

In article <1992Aug7.203735.18451@alc.com> stassen@alc.com 
     (Chris Stassen) writes:

>In article <22719@hacgate.SCG.HAC.COM> frazier@maxwell 
     (Greg Frazier) writes:

>> Well, considering how little sharks have changed over the millenia,
>> that person could be right (coelcanth's would also have to be
>> considered as "perfect animals", and maybe dragonflies, too).
>
>That the coelacanth has survived "unchanged" over time is something of a
>myth.  The surprise in finding a coelacanth was that the lineage had been
>thought extinct -- not that the existing fish was identical to its
>ancestors.  (This comment is often seen in popular literature,
>though.)

I'm surprised that Chris took issue with this vis a vis the
coelocanth, but nobody else has taken issue with the statements about
sharks.  

>I've recently seen a photo of a modern C. beside a reconstruction of one
>from the fossil record; they look quite different.  The basic shape and
>features are similar, but the proportions are noticeably different (the
>teeth, in particular, are very dissimilar). 

Similar things could be said about sharks.  I can't recall as that
I've seen pictures, but I've seen drawings of the Devonian shark
_Cladoselache_, and although it's easy to see from those that
_Cladoselache_ should be classified as a shark, it doesn't actually
look like any particular modern shark.  Sharks have most definitely
been changing throughout their history.

In article <1992Aug5.164047.2700@dsg.cs.tcd.ie>,
sloubtin@dsg.cs.tcd.ie (Sylvain Louboutin) wrote:

>Sharks reached perfection in the sense that they are perfectly
>adapted to their environment and do not need to evolve anymore (if I
>recall the Cousteau's book about sharks, they more or less kept the
>same form for quite a few million years)...

While I have little doubt that Cousteau has said such things, I'd take
them with a large dose of salt.  A few years ago it was demonstrated
that great white sharks maintain their body temperature above that of
the surrounding water, probably by diverting blood flow around their
muscles where it can be warmed by metabolic activity.  These sharks
prey on mammals, so they *need* that adaptation.  Without it they
would not be able to keep up with a seal that swam down to colder
water in an effort to elude its fate.  For the sharks, this is a
relatively recent need, since seals haven't been swimming in the ocean
any where near as long as "sharks" have.

Although the general shape of many sharks is similar to that of
_Cladoselache_, (though for others it is not at all--witness the
woebegone shark and the manta ray for a couple of nice
counterexamples) I think it's patently absurd to say that sharks are
"perfectly adapted to their environment" and hence are unchanging.

//Sylvain R.Y. Louboutin, fax: (+353-1)772204, e-mail: Louboutin@dsg.cs.tcd.ie

Mickey Rowe     (rowe@pender.ee.upenn.edu)
Xref: sparky talk.origins:9449 sci.skeptic:14216