Who is playing that game? You wanted a transitional fossil and you got
one. But now you have diverted twice: once by saying that it was useful
and now by saying something about simple-to-complex, which is not what I
was talking about at all. A scale is not a simple thing. Neither is a
feather.
>
>Let's get clear on what we don't know. How do you back up the claim that
>a given structure is a transitional form? You can see that form B is
>intermediate in structure between form A and form C, but what else do
>you know?
We have the wings of longisquama which are clearly modified scales. The
shape of the modification is to make the wing feather shaped. A feather is
made of similar material as the scale and thus is materially linked. The
morphology of the longisquama wing is intermediate between that of a
feather (which is fragmented) and a scale which is short and solid.
Longisquama's wing is solid.
Finally, the Longisquama wing is prior to the advent of any feather on
earth. So temporally, the thing fits, morphologically the thing fits, and
materially the thing fits. You just don't want it to be transitional. I
will acknowledge that there are some paleontologists who do not accept
longisquama as a ancestor for feathers. Others do.
How do you know forms A, B, and C aren't independently evolved
>from form X? Is an intermediate necessarily transitional? If it is
>transitional,
>how do you know in what direction the transition is proceeding?
Well, considering that there were no feathers in the fossil record in rocks
earlier than this, and there are feathers in the next geologic era, gives
us a clue as to which direction the transformation was occurring. If you
would pay attention to the ages of the Longisquama (Triassic) and the age
of the first bird (Jurassic) you would know that the transition is
proceeding from NO feathers to feathers. This is not a being that is after
the appearance of the first bird.
Do you
>have fossil series showing change over time among unquestionably related
>organisms, as in the eohippus>equus series? No, you don't.
No, I don't. But there is lots of other reasoning that supports the
hypothesis.
>
>>Which is clearly untrue given the elongated, feather-like scales of
>>longisquama.
>
>The tree of life is more like the creationistic candelabra of long lines
>evolving vertically and independently, than like the ever-branching
>Darwinian bush. I'd rather think about the origin of the candelabra
>than look for transitional forms that aren't there. Personally I favor
>feathers evolving from complex spines, and I'd guess 'feather-like
>scales' evolved from the same structure feathers evolved from.
OK, where are the complex spines in the fossil record? What animal has these?
>I take seriously the principle of reduction and specialization of skeletal
>segments. I'd be okay with Ichthyostega as the ancestor of all terrestrial
>quadrupeds, if this animal had enough bones in the digits to evolve into
>primates, for example, through a process of reduction. But it doesn't.
au contraire, it does. THis is from my web page and you can verify what I
say in the references there:
"Ichthyostega is the first animals with feet but they are different than
most tetrapod feet. They are much like Acanthostega but has 7 digits on his
hindlimb. His legs were only good for being in water. They could not
support his weight.(Coates and Clack, 1990, p. 67) These are half evolved
legs since they have more digits than the normal tetrapod but fewer bony
rays than the fish and they are unable to support the weight. This
contradicts Gish's statement that there are no half-evolved feet. (Gish,
1978, p. 79) .
With 7 digits reduction can reduce the number of digits to 5. So I don't
understand what your objection is.
>Ichthyostega was evidently a quite successful form, well-adapted to its
>niche, judging from the number of fossils. Intermediate, yes. Related to
>lungfish, yes, but more likely a cousin than a direct descendant.
I don't think many would argue that we can never know the animals that are
directly upon the line of descent. But we can get close
>Transitional? Possibly it's an ancestor of certain other quadrupeds; we just
>don't know. Only the rigorous application of the gradual simple-to-complex
>paradigm gives Ichthyostega an exalted evolutionary status.
The problem with your line of reasoning is that a fish fin has more digits
than the real numbers have numbers. Reduction of the number of fin bones
can and must have occurred just as you suggest. So, the transition from
fish to amphibian was in some sense from complex to simple.
>>>Pinnipeds have lost much of their limb structure; do you think that if
>>>they were gradually forced to abandon the sea they would get that limb
>>>structure back?
>
>>Dollo's Law seems to preclude this. It is the observation that a structure
>>once lost is never regained.
>
>How do you reconcile Dollo's factual generalization with your belief that
>skeletally
>elaborative gradual evolution occurs?
Woah. I didn't say I believe in 'gradual' evolution. I believe that
punc-eq is a much better model. It fits with nonlinear systems which is
what life is, and it fits the data of paleontology better.
If a species needed (so to speak) to
>re-evolve
>a lost structure, why couldn't it? Wouldn't some residual embryonic
>canalization
>facilitate such re-evolution?
Basically it boils down to chance. THe odds against getting the same
genetic draw after a bunch of mutations have happened is akin to the odds
of drawing the identical bridge hand twice in a row for all four players.
The pattern of reduction explains the inability
>to
>re-evolve a structure. When the parts are gone, they're gone for good. Of
>course,
>functional equivalents of a structure can evolve by means other than
skeletal
>elaboration, that is, through distortion of the remaining parts.
Not always forever, there are whales that are born with feet, there are
occasional snakes born with feet, there are occasional horses born with
three toes as their ancestors and Caesar was said to have ridden a 5-toed
horse.
Occasionally things can come back. Dollo's law really is a probability law
that says it is extremely unlikely, but not impossible.
glenn
Foundation, Fall and Flood
Adam, Apes and Anthropology
http://www.flash.net/~mortongr/dmd.htm
Lots of information on creation/evolution