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Re: Birds and Cretins



Shaun Cronin wrote:

>One of the creaitionists I have contact with posted this recently;
>
>>Archeopteryx? Steven Jay Gould, himself, said that it is a "curious mosaic=
"
>>that does not count as an intermediary fossil (Paleobiology, 3:147, 1977).
>>Another problem: recent discoveries near Post, Texas reveal fossils of bir=
ds
>>that are (supposedly) 225 million years old... older than Archaeoptyrx. If=
 it
>>is truly an intermediate between reptiles and birds - how is it that birds=
 are
>>found that are some 75 million years older? Weren't reptiles "in vogue" at
>>that time?
>
>Can someone give me the context of the Gould qoute and what he really
>meant. Also does anyone know what the supposed 225myr Texas bird fossils
>are all about? Is this claim a new creationist lie?

"At the higher level of evolutionary transition between basic morphological
designs, gradualism has always been in trouble, though it remains the
'official' position of most Western evolutionists.  Smooth intermediates
between Baupl=E4ne are almost impossible to construct, even in thought
experiments; there is certainly no evidence for them in the fossil record
(curious mosaics like Archaeopteryx do not count)" (Gould & Eldredge 1977,
p. 147).

The article in question is a discussion of punctuated equilibrium and how
the evidence from the fossil record does not support a purely gradualistic
evolutionary model.  Eldredge and Gould point out that intermediates, for
the most part, do not exhibit such smooth evolution, but that features
evolve at differing rates.  In this they were following the ideas put
forward by de Beer (1969), who suggested that,
"the statement that the animal was intermediate might mean that it was a
mixture and that the transition affected some parts of the animal and not
others, with the result that some parts were similar to those of one type,
other parts similar to another type, and few or no parts intermediate in
structure.  In such a case the animal might be regarded as a mosaic in
which the pieces could be replaced independantly one by one, so that the
transitional stages were a jumble of characters, some of them similar to
those of the class from which the animal evolved, others similar to those
of the class in which the animal was evolving.
If now it be asked what kind of transition is shown by Archaeopyteryx , the
answer is perfectly clear.  It is a mosaic in which some characters are
perfectly reptilian and others no less perfectly avian." (p. 133-134)

Thus being a "mosaic" does not disqualify a form from being an
intermediate, merely a **smooth** intermediate. Indeed, this particular
quote has been misused by so many creationiats that is prompted Gould to
write:

"since we proposed punctuated equilibrium to explain trends, it is
infuriating to be quoted again and again by creationists - whether through
design or stupidity, I do not know - as admitting that the fossil record
includes no transitional forms.  Transitional forms are generally lacking
at the species level but are abundant between larger groups." (Gould 1984,
p. 260).

Even more specifically, Gould (1991, p. 144-145) states that
"Archaeopteryx, the first bird, is as pretty an intermediate as
paleontology could ever hope to find."

The Texas 'bird' is _Protoavis_. However, its avian affinities have yet to
be substantiated.
There are major problems with _Protoavis_. On the Chatterjee (1991)
interpretation, Ostrom (1991) has this to say [my paraphrase]: The only
published material from the fossil is a monograph in the Philosophical
Transactions of the Royal Society of London.  However, this only describes
the head.  This is badly crushed and all the pieces have been extracted
from the matrix, rendering precise placement of the pieces open to
question.  The description is done from an avian viewpoint, with no
counterview (e.g. is this a dinosaur?) used. The skull is so badly crushed
that diagnostic features are not preserved.  Therefore the published
material does not support the view that this
is a bird.  Indeed a viewing of the fossil by Ostrom (in admittedly less
than ideal surroundings) showed that the diagnostic features which could
identify the fossil either way are badly crushed and it is doubtful whether
any definitive statement could be supported by the fossil. It may be a
bird, it may not.

Chatterjee, S. (1991)  Cranial anatony and relationships of a new
Triassic bird from Texas. Phil. Trans. R. Soc. Lond. B. 332: 277-342

de Beer, G. A. 1969. Streams of Culture. J.B. Lippincort, Philadelphia. 237 =
pp

Eldredge, N. & Gould, S. J. 1977. Punctuated equilibrium: the tempo and
mode of evolution reconsidered. Paleobiology, 3: 115-151

Gould, S. J. 1991. Bully for Brontosaurus. Penguin, London. 540 pp.

Gould, S. J. 1984 Hen's Teeth and Horse's Toes, Penguin, London.

Ostrom, J.H. (1991)  Bird in the Bush. Nature, 353: 212

Chris

cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
-------------------------------------------------------------------
Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.