I must preface my sceptical comments that under my Mediate
Creation model I do not rule out that birds came from reptiles-indeed
from their general morphological similarities and order of appearance
in the fossil record I think it highly likely. I do not even rule out a
Darwinian, step-by-step `blind watchmaker' fully naturalistic process,
because the Biblical God is fully in control of apparently random
events (1 Kings 22:34; Proverbs 16:33). But because Darwinian
macroevolution has such a poor fit with the evidence, I expect that God
intervened at strategic points in biological history, just as He has in
human history. Such fast-transitions would not be very likely to
appear in the fossil record, or be easily linked to their ancestors,
as Gould points out:
"Two different kinds of explanations for the absence of Precambrian
ancestors have been debated for more than a century: the artifact
theory (they did exist, but the fossil record hasn't preserved them),
and the fast-transition theory (they really didn't exist, at least as
complex invertebrates easily linked to their descendants, and the
evolution of modern anatomical plans occurred with a rapidity that
threatens our usual ideas about the stately pace of evolutionary
change)." (Gould S.J., "Wonderful Life, 1991, pp270-272)
On Thu, 22 Jan 1998 16:12:00 -0600, Kevin Koenig wrote:
KK>A colleague and I have gone through the 1/8, vol.391 of Nature
>rather thoroughly. :-) We came upon the article, An exceptionally
>well-preserved theropod dinosaur from Yixian Formation of China.
>We took note of figure 2b, specifically "The integumentary
>structures are along the dorsal side and the tail . . . "
>
>Now in the same volume under news and views; Feathers,
>filaments and theropod dinosaurs; bottom of second paragraph, ".
>..some are already incorporating Sinosauropyeryx into models for
>the origin of feathers and flight. Still others argue that the feathers
>are merely an artifact of preservation."
Interesting, scientific journals take a few weeks to get out to the
antipodes, but I saw the following brief report on the web at
http://www.nature.com/Nature2/serve?SID=5125902&CAT=TOC&PG=19980101 /
toc.html (you will have to sign on for a free subscription):
"An exceptionally well-preserved theropod dinosaur from the Yixian
Formation of China Two spectacular fossilized dinosaur skeletons
were recently discovered in Liaoning in northeastern China. Here the
authors describe the two nearly complete skeletons of a small
theropod that represent a species closely related to Compsognathus.
Sinosauropteryx has the longest tail of any known theropod, and a
three-fingered hand dominated by the first finger, which is longer and
thicker than either of the bones of the forearm. Both specimens have
interesting integumentary structures that could provide information
about the origin of feathers. The larger individual also has stomach
contents, and a pair of eggs in the abdomen. P-j Chen, Z-m Dong &
S-n Zhen, An exceptionally well-preserved theropod dinosaur from
the Yixian Formation of China (Article) Nature 391, 147 (1998)
This account seems to be a bit vague about what exactly are these
"interesting integumentary structures that could provide information
about the origin of feathers". According to my Oxford Concise
Dictionary, the "Integument" is "1. The outermost body layer of an
animal..." or "2. The outer protective covering of a plant ...."
Therefore "integumentary structures" could be just scales, or even
upright fins like Stegosaurus. Norman mentions a puzzling group of
fossils from Mongolia which have long claws:
"Lastly there is a group of theropod fossils from Mongolia which have
been given various names and may represent a totally puzzling group
known as segnosaurs. It is not even certain if these are theropods,
but whatever else they are they are strange. They have partly
toothless beaks, enormous sickle-shaped claws 2ft (60cm) long or more
on their hands, broad feet, and a pelvis which looks very similar to
that of an ornithischian dinosaur." (Norman D., "Dinosaur!", 1991,
p52).
If these were not theropods, then the problem that theropod and bird
digits follow a radically different embryological development pattern
(see Knight J., "Dinosaur theory put to flight," New Scientist, Vol
156, No 2106, 1 November 1997, p20), would not arise. But if they
are theropods, then it is difficult to understand how they could be
closely related to birds.
KK>We found it interesting that the "artifacts of preservation" appear
>only on the back, tail and belly. These are places where one
>would assume feathers, hairs or some kind of filamentous structure
>would appear.
Reptiles did not have "hair"-that is one of the defining
characteristics of mammals. And I would have thought that "feathers
would appear on the proto-bird's forelimbs!
Even if this dinosaur turns out to have feathers, that will not mean
we are one iota closer to understanding how they were developed from
a reptile scale by a Darwinian, step-by-step, process. There are
enormous problems with understanding how feathers arose from
reptilian scales, as this excerpt from a recent article in the
Journal of Evolutionary Biology shows:
"It has been a truism for most of this century," A.H. Brush
(Physiology and Neurobiology, University of Connecticut) notes, "that
feathers are related to reptilian scales." Yet, he continues, "the
molecular evidence questions the simple, direct relation of the
specialized structures of birds to reptile scale. I will provide
arguments to show that reptile scales and feathers are related only
by the fact that their origin is in epidermal tissue. Every feature
from gene structure and organization, to development, morphogenesis
and tissue organization is different" (p.132). Feathers appear
suddenly in the fossil record, Brush observes, as an "undeniably
unique" character distinguishing birds (p. 133). Current approaches
to the origin of feathers, Brush worries, tend to focus "on why
feathers evolved or where feathers came from. At this juncture
neither is as illuminating as to ask how they arose" (p. 133).
Brush examines the protein structure of bird feathers and argues that
it is "unique among vertebrates," with the "ancestral reptilian
epidermal structure...still unidentified" (p. 131). He concludes:
"At the morphological level feathers are traditionally considered
homologous with reptilian scales. However, in development,
morphogenesis, gene structure, protein shape and sequence, and
filament formation and structure, feathers are different. Clearly,
feathers provide a unique and outstanding example of an evolutionary
novelty" (p. 140)." ("The Enigmatic Origin of Feathers", Origins &
Design, Vol. 17, No. 2, Spring 1996, p17).
I will add some more:
1. There are no known intermediates between scales and feathers in
the fossil record
"There are no recognized intermediates in the fossil record and our
concepts of any protofeather are speculative and often depend on
interpretations of behavior rather than structure." (Brush A.H., "On
the origin of feathers," Journal of Evolutionary Biology, 9, 1996,
pp131-132)
2.There is no hard evidence for the preadaptative (or exaptative)
role of feathers in thermoregulation:
"Debate over their possible role in thermoregulation or the origin of
flight is still unsettled...." (Brush, 1996, p132)
3. The feather is a complex novelty involving cascading levels of
complexity (not bad for an blind watchmaker!):
"A hierarchical scheme may be useful in understanding the
evolutionary emergence of feathers. The essential `hard wired'
information in the system resides in the nucleotide sequences of the
DNA and just about everything else is derived from the sequential
information flow through a series of processes that follow accepted
laws of chemistry and physics....Novelty at one level implies, and
presumably requires, novelty at a preceding level. The appearance of
a morphological novelty implies change in the genome, cell structure
find function, or in timing of gene expression or organizational
changes...It is...not possible to predict the shape of a feather from
gene nucleotide sequence or the gene's chromosomal organization"
(Brush, 1996, p133)
4. Bird feather-genes may share a common ancestor with bird scale,
beak and claw genes:
"the proteins and genes of feather and scale (presumably including
beaks and claws) are similar enough to imply a common ancestor."
(Brush, 1996, p136)
5. However, there is no molecular evidence that bird
feather/scale/beak genes are related to reptilian scale-genes or
other skin genes:
"There are no compelling matches between avian feather, scute, claw
or beak and proteins from reptilian epidermal structures or the
alpha- keratins of the soft skin in birds, reptiles or mammals."
(Brush, 1996, p136)
6. The feather-gene may have been formed by the "shuffling" of parts
of at least three other avian genes:
"Given the novel character of feather it is of interest to propose a
molecular model for the evolution of the structure. I submit that
the original gene was formed by shuffling [of] at least parts of
three others. These included specifications for the beta-pleated
sheet, the shorter globular portion, and the longer globular wing
with the repeated tripeptide (Gly-Gly-X) included." (Brush, 1996,
p136)
Sounds like pretty clever genetic engineering to me!
7. The feather required "simultaneous and important changes" at four
levels:
"It is clear that the appearance of novel structures requires
simultaneous and important changes at the genic, cellular, tissue and
organismal levels (Ashley and Hall, 1991). (Brush, 1996, p140).
I would have thought that important changes simultaneously at four
separate levels is a pretty good description of a genetic miracle!
As a creationist, I could not ask for better evidence of
intelligent design in the origin of feathers than what this
article in the Journal of *Evolutionary* Biology!
KK>Does anyone know how or what produces artifacts of
>preservation? Why don't these artifacts of preservation appear
>around the open mouth, in between toes, around legs or under the
>chin?
When things fossilise, skin and bone is replaced by minerals. I
presume this process can sometimes cause its own side-effects (eg.
cracking of mud, etc). Also, I have heard that when one dies, ones
fingernails and hair keep growing for a while. In the case of a
reptile, a possibility is that the scales might keep growing after it
has died and been covered by mud. Alternatively, the scales might
flake off. Any of these possibilities might look like feathers.
Recently there was a report of another "feathered" dinosaur which
turned out not to be.
Regards,
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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