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Re: Coelacanth article in current NatGeo

As some additional food for thought with regards to fin evolution, consider 
that free-swimming organisms have a challenge in the sense that rapid starts 
are best initiated using large fluid forces at a low L:D ratio ("drag-based" 
locomotion) while sustained swimming tends to be most efficient and rapid using 
moderate to large fluid forces at a high L:D ratio ("lift-based" locomotion).  

Fleshy fins are one potential solution to this problem, as they can be used as 
either a drag-based paddle or a lift-based hydrofoil depending on the 
orientation of the limb element.

An alternative is to have compliant fins, but a flexible body that can bend 
sufficiently to serve as a drag-based paddle during fast starts.  The latter 
solution is what ray-finned fish (especially teleosts) generally use, with a 
few exceptions.  The fast-start mechanic is of such importance that up to 75% 
of the muscle mass in some taxa is devoted almost exclusively to fast-start 
usage, acting as payload the rest of the time.  Of course, in teleosts 
especially, this involves a major reorganization - not only are the fins 
compliant, but the pelvic and pectoral girdles are shoved up behind the head, 
making most of the length of the animal effectively a hypertrophied "tail" 
involved in propulsion.  The compliance of the ray-fins is then useful for 
other aspects of control and propulsion.  Note than in secondarily stiff-bodied 
fish, such as surgeonfish and triggerfish, the pectoral fins have become 
secondarily fleshy, and are used in an aquaflying manner for primary propulsion.



Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
(443) 280-0181

On Feb 24, 2011, at 1:00 PM, Augusto Haro wrote:

> I think Choo is right. Chondrichthyans also have fleshy fins, thus
> suggesting fleshy fins came first. Thus, the reason by which fleshy
> fins were good may reduce to the reason by which fins are good. Now,
> it may be asked why ray fins are more adaptive, if they persisted
> because of intrinsic adaptive superiority and not because of luck at
> the mass extinction (or because of other improvement in
> actinopterygians).
> 2011/2/24 Erik Boehm <erikboehm07@yahoo.com>:
>>>>   Maybe my understanding of
>>> their diversity is wrong, but it seems odd
>>>>   that at one point there were so many fleshy
>>> finned fish, and now
>>>>   there are almost none.
>>> A couple of mass extinctions.
>> Of course, but prior to those, the lobe fins were not restricted to 
>> bottom/river dwellers correct? if so, what purpose did those fleshy fins 
>> serve?
>> Its my understanding the basal lobe fins did not live in rivers, or along 
>> the sea floor, where such fins may have been useful for holding the fish 
>> against a surface. What was the original use?