SJ>On Mon, 19 Jan 1998 22:13:54 -0600, Glenn Morton wrote:
>GM>There is a report in the January 8, 1998 Nature about a fossil fish with
>>fingers in its fin. From the news account on the AP wire it sounds like it
>>is a lobe-finned fish, a coelacanth. It comes from 350 million years ago
>>which is immediately after the evolution of the amphibians (who also had
>>fingers). I hope to have the article in my hand tomorrow...
SJ>...I haven't seen the NATURE article yet, but maybe
>its the Western Australian Devonian fish fossil, Gogonasu, which was
>in one of our local newspapers a while back:
I now have the article, and it is yet another problem for Neo-Darwinist
adaptationism. A fish grew fingers *before* it needed them on land:
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Fish with fingers?
Fingers and toes were long thought to be novelties associated with
the invasion of land by tetrapods. The recent identification of a
variety of aquatic specializations in some early tetrapods has
provoked a debate on whether digits arose in primarily terrestrial or
aquatic animals' 2. We recently discovered a pectoral fin of a lobe-
finned fish (Fig. la, b) that is remarkably similar to tetrapod limbs.
This discovery reveals that major tetrapod novelties are also seen in
the paddles of some closely related fish and therefore need not have
arisen to meet the demands of a terrestrial existence.
We discovered the new fin along a roadside in north central
Pennsylvania (Catskill Formation; Late Devonian; ~370 Myr BP).
Features of the shoulder girdle and fin rays clearly identify it as
belonging to a rhizodontid sarcopterygian 3. The specimen o Spares
favourably with Sauripterus, Id own from a single specimen
discovered in 1840, in having a broadly flattened radius. The quality
of preservation of the new fin permits comparisons with limbs that
were impossible until now.
The closest relatives of tetrapods, 'osteolepiform' and elpistostegalid
sarcopterygians 4, have fins designed on a simple bifurcate pattern
and do not have structures that can be readily compared with digits
(Fig. lc). In contrast, the new fin contains an array of eight distally
facing and jointed preaxial radials that are superficially similar in
number and configuration to the digits of early tetrapods (Fig. ld). In
addition, six of these radials articulate with homologues
The carpus (intermedium and ulnare) at a common proximo-distal
level. The radials of the new fin differ from tetrapod digits in that they
are flattened and encased by stiff unjointed dermal fin rays (Fig. la, b).
Taken together, these characteristics suggest that the digit-like
structures were not the primary load-bearing elements of the distal
portion of the rhizodont appendage.
Phylogenetic comparisons with other sarcopterygians are complicated
by missing data but current hypotheses place rhizodontids just outside
a group containing 'osteolepiformes, elpistostegalids and tetrapods 4;.
This suggests two possibilities: fingers are either primitive to stem
tetrapods, or digit-like structures evolved independently in a closely
related group of Devonian fish. Either phylogenetic interpretation
forces us to question the use of digits as a key innovation associated
with the origin of tetrapods.
This discovery reveals that some Devonian fish acquired a truly
mosaic fin skeleton, possessing both an extensive and limb-like
endoskeleton and elaborate dermal fin rays. The presence of digit-like
structures in the paddle of an aquatic fish suggests that digits could
have evolved for reasons other than bearing weight during terrestrial
locomotion.
(Daeschler E.B. & Shubin N., "Fish with fingers?", Nature, Vol 391,
8 January 1997, p133)
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Steve
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Stephen E (Steve) Jones ,--_|\ sejones@ibm.net
3 Hawker Avenue / Oz \ Steve.Jones@health.wa.gov.au
Warwick 6024 ->*_,--\_/ Phone +61 8 9448 7439
Perth, West Australia v "Test everything." (1Thess 5:21)
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