In the original post on the alleged fish to amphibian
transition, reference was made to Phillip Johnson's use of a
statement by Barbara Stahl, but the statement itself was not given.
It was suggested that Dr. Stahl's statement was nothing more than
an acknowledgement of the fact that fossils do not come with signs
reading "Here lies your Great-Grandfish." My reason for quoting
Dr. Stahl in my response to that post was to show that her
criticism of the fossil record for tetrapod ancestry was not so
shallow. As I stated, "It seems clear that her objection to the
various fish which have been put forth as tetrapod ancestors is not
that they lack signs announcing their ancestral status but that
they lack evidence of developing the structures which most
distinguish early tetrapods." The issue was whether Dr. Stahl's
criticism of the fossil record had been brushed aside by being
mischaracterized.
I pointed out in my first post that a *transitional* creature
is by definition one that comes between or connects two other
creatures. In the evolutionist's scheme, for example, the first
living cell was not a transitional life form; rather than being a
bridge, a transition between two life forms, it was the *original*
life form. That is why it is incorrect to speak of Sarcopterygii
(the lobe-finned, air breathing fishes) as transitional creatures
without persuasive evidence that they descended from some other
fish. Until then, the creationist will consider that they were an
original life form, just like the evolutionists' first living cell.
Labeling them transitional simply begs the question.
The issue in tetrapod evolution is not whether fishes with
gills and lungs are transitional, as I have defined it above, but
whether a compelling case can be made that the first tetrapod
descended from such a fish. Assuming that _Acanthostega_ was the
first tetrapod (it is not the oldest in the fossil record) and that
it possessed gills and lungs (which I am not prepared to concede),
the gill/lung similarity would be just one piece of evidence to be
considered in assessing the claim that this creature descended from
a sarcopterygian. That similarity would help the evolutionist's
case, but it would by no means be dispositive. After all, if the
Sarcopterygii were created complete with gills and lungs, as is
suggested by the absence of any ancestors for them in the fossil
record, then creationists can be forgiven for denying that gills
and lungs could only appear in the first tetrapod by inheritance.
At the risk of stating the obvious, the matter boils down to
whether one believes that the morphological gap between any of the
sarcopterygians and the earliest tetrapod was crossed by Darwinian
processes without leaving a trace of the forms that must have
existed between them. As the evolutionist sees it, the gap is too
small and the vagaries of fossilization are too great to expect,
let alone demand, fossil evidence of the transition. As the
creationist sees it, the gap is so large that the number of
transitional forms needed to cross it would be too great to
completely escape fossilization and discovery. These differences
in how one weighs the evidence have much to do with one's philo-
sophical or theological commitments.
It is in this context that statements from internationally
known evolutionists, such as Robert L. Carroll and Keith Stewart
Thomson, that there are no transitional forms between fishes and
tetrapods take on such importance. Their philosophical lenses are
finely ground for seeing transitional forms. If with full
knowledge of _Acanthostega_ and the panderichthyids, Dr. Thomson
can declare that "we still do not have any really intermediate
fossil forms between fishes and tetrapods," how can creationists
who hold that same opinion be viewed as zealots who care nothing
about the data?
Now about the tetrapod trackway evidence from the Lower
Devonian described by Anne Warren, Robert Jupp and Barrie Bolton in
"Earliest tetrapod trackway," _Alcheringa_ 10: 183-86 (1986). In
the first place, it seems inconsistent to chastise Phillip Johnson
for failing to mention that the coelacanth is in a different
suborder than _Latimeria_ but to take no similar umbrage at the
failure of Ahlberg and Milner to advise their readers of this
anomalous trackway evidence. As I understood the criticism of
Professor Johnson, he had failed to provide the reader with the
information necessary to permit a personal evaluation of his claim.
That seems to apply with even greater force to the omission by
Ahlberg and Milner.
The analysis of this trackway that was offered in the response
to my post highlights how the weighing of evidence is influenced,
if not determined, by one's prior position on an issue. The reader
should consult the article for himself, but the bottom line is that
the evidence was sufficient to convince the zoologists and
geologist who studied the find that it was indeed a tetrapod
trackway dating from the Lower Devonian. Glenn rejected their
conclusion, however, because it had not been proven beyond a shadow
of a doubt. He pointed out that "there remains a *small doubt*" as
to whether the fossil slab had come from the Grampian Group, so
"there is *some uncertainty* in the age." He quoted the authors'
admission that "there is *no certainty*" that the marks form a
tetrapod track (because digit impressions were not preserved). So
when it comes to evidence contrary the evolutionist's scenario,
probability doesn't cut it.
Now compare this to the much lower standard of proof Glenn
used to assess evidence he believes favors evolution. When Coates
and Clack say that the hindlimb of _Acanthostega_ "could *probably*
not be brought into weight-bearing position," that the forearm
bones "*suggest* that the forelimb could never have flexed from the
elbow to be in a fully load-bearing posture," and that _Acantho-
stega_ "*seems* to have retained fish-like internal gills," this is
accepted as fact. If the creationist takes the same skeptical
approach to the conclusions of Clack and Coates that the evolution-
ist takes with regard to the conclusions of Warren, Jupp, and
Bolton, the creationist is considered "scientifically challenged."
There is an undeniable element of truth in Paul Simon's lyric, "A
man hears what he wants to hear and disregards the rest."
In place of the conclusion of Warren, Jupp, and Bolton, Glenn
suggests that the trackway was made by panderichthyids rather than
tetrapods. He is undaunted by the fact these scientists rejected
the proposal that the tracks had been made by a tetrapod walking in
shallow water. They state (p. 185) that this "is an improbable
solution because such poorly consolidated sediments are unlikely to
preserve tracks made *subaqueously*" (emphasis mine).
Even if that were not the case, where is the evidence that a
panderichthyid or any other rhipidistian could make such tracks?
The statement by Clack and Coates that some modern fish use fins
for "stalking" is inadequate for several reasons. First, there is
no indication of how far these fish travel when engaging in this
behavior. Second, there is no hint that a "stalking fish" would
leave tracks like a tetrapod (which seems highly unlikely given the
extreme differences in limb shape and attachments). Third, there
is no reason to believe that the rhipdistians possessed the
stalking behavior of the fishes mentioned by Coates and Clack.
None of these fish are even in the same subclass (Sarcopterygii) as
the panderichthyids, and even if they were, it was Glenn who argued
(in criticizing Johnson) that one cannot attribute the traits of
modern creatures to their distant relatives.
Lastly, it strikes me as unfair to criticize creationist
authors for not addressing alleged transitional forms that did not
become known until after their books were written. I expect that
these new claims will be analyzed in future material.
Ashby