Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!tdatirv!sarima
From: sarima@tdatirv.UUCP (Stanley Friesen)
Newsgroups: sci.bio
Subject: Re: Coelocanth and evolution:x
Message-ID: <18@tdatirv.UUCP>
Date: 4 Jun 91 18:30:28 GMT
References: <17580003@hpfcdj.HP.COM>
Reply-To: sarima@tdatirv.UUCP (Stanley Friesen)
Organization: Teradata Corp., Irvine
Lines: 57

In article <17580003@hpfcdj.HP.COM> sharp@hpfcdj.HP.COM (Darrin Sharp) writes:
>	Last night, on the "National Geographic Explorer",
>	there was a segment on the coelocanth (sp?). This
>	is a fish that was thought to be extinct, but live
>	specimens were rediscovered in the 1930's off the
>	S.E. coast of Africa. Since then, several are
>	caught each year.

Sigh, I would have hoped NGE would get this right.  The coelacanth is a
species in a *group* of fish that was thought to be extinct.  The living
species of coelacanth was completely unknown prior to its discovery in
the '30's.  It closest known relatives are fossils from many millions of
years ago.  There are not even any fairly recent fossil relatives.  Thus,
in the absence of any 'recent' fossils or any known recent species the
whole group was assumed to be extinct.

>	The show made mention of the fact that these fish
>	were unchanged for the last 400 million years.

Bull****!  They are *little* changed, having essentially the same anatomy
as their 400 MY old relatives.  But in many details, some of them
significant, they have changed considerably.

It is easy for even a non-biologist to tell the difference between the
coelacanth and it closest (400 MY old) relative.  They *look* different.
[About as different as a goldfish and a river carp].

>	I know that outwardly, the live specimens very closely
>	resemble the 400 million year old fossils. But how
>	can this be? Is it common for organisms to not evolve
>	for 400 million years? How long has it been since sharks
>	and alligators/turtles/crocodiles evolved? Any other
>	species that haven't changed in this long? 

*No* species are unchanged for this long.  NGE was wrong.

The earliest sharks probably predate the lobe-fin fishes (the group to
which the coelacanth belongs).  They were, however, quite different
than modern sharks.  Sharks of more or less modern aspect appeared very
early though, perhaps about the same time as the earliest lobe-fins.
And the modern sharks are about as similar to these early sharks as
the living coelacanth is to its early relatives.

Crocodiles of more or less modern form appeared about 150 MY ago (give or
take 20 MY).  Except for size these would be almost indistinguishable
from modern forms (except to an expert).  The earliest crocodiles appeared
about 220 MY ago.  But these forms were very different, and I think even
a layperson could tell them from modern crocs.  (Alligators are, to a
biologist, essentially just specialized crocodiles).

Turtles are, for land animals, very ancient.  The lineage may go back as far
as 300 MY with almost no change in basic anatomy.  (I am unsure of the dates
here, I have not studied turtles in any depth).
-- 
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uunet!tdatirv!sarima				(Stanley Friesen)