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On Sat, 01 Mar 2003 00:05:49 -0800, Cliff Lundberg wrote:

>SJ>There is no doubt that Archaeopteryx is very similar morphologically to
>>some "Dinosaurs", but such similarity does not necessarily indicate close
>>relationship, since it could be due to convergence.
>>...
> >... similarity can be due to convergence, i.e. analogy not homology.

CL>I wonder, which similarities between A. and some dinosaurs would Steve
>attribute to convergence rather than parallelism?

I am afraid I don't understand Cliff's question. AFAIK "parallelism" (aka
"parallel evolution") is basically the same thing as "convergence", i.e.
similarity of characters due primarily to similarity of environment, rather
than to shared common ancestry:

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http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=parallelism ...
Main Entry: parallelism ... noun Date: 1610 ...
5 : the development of similar new characters by two or more related organisms
in response to similarity of environment -- called also parallel evolution

http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=convergence ...
Main Entry: convergence ... Function: noun Date: 1713 ...
3 : independent development of similar characters (as of bodily structure
or cultural traits) often associated with similarity of habits or environment
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CL>That is, which features
>were evolved de novo and are similar only because they evolved to fulfill
>the same function, and which features are similar because they are
>homologous to a feature in a common ancestor?

From this I will therefore assume that Cliff means "which similarities
between" Archaeopteryx "and some dinosaurs" (e.g. theropod
dromaeosaurs) "would" I "attribute to convergence rather than" to shared
common ancestry?

Well first of all, the paleontologist/cladist, and editor of NATURE, henry
Gee, who is a proponent of the bird from dinosaur theory, admits that "The
claim of convergence is the most important objection to the bird-dinosaur
link" (see tagline).

And since even he finds that "Convergence is an extremely difficult
problem" and even for the experts like him, "When confronted by two
superficially similar organisms, it is not always easy to spot whether their
similarity is a result of shared common ancestry, or an adaptive response to
similar pressures in otherwise unrelated animals" (see tagline), I must
confess that as a mere second year Biology student, I don't know the answer
to Cliff's specific question.

But I have another way (which Cliff just ignored) of answering Cliff's
question, namely what I said about the ratites:

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On Sat, 01 Mar 2003 06:49:32 +0800, Stephen E. Jones wrote:

>While I have no problem if it turned out that Archaeopteryx (and hence all
>"Birds") is descended from "Dinosaurs", I personally think it is more likely
>that Archaeopteryx and "Dinosaurs" shared a common ancestor.
>
>A main reason is the typical Gondwanan distribution of the Ratites, e.g.
>emu, cassowary (Australia), ostrich (Africa) and rhea (South America)
>which are flightless and primitive, yet true birds. The exclusively southern
>distribution of that other flightless bird, the penguin, supports this.
>
>Being flightless, it is much more likely that birds originated in Gondwana
>before its split up ~100 mya, and therefore the Chinese `feathered'
>dinosaurs at 120 mya are unlikely to have anything to do with the origin of
>birds.
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Since the ratites do have a typical Gondwanan distribution (Emu &
Cassowary = Australia, Kiwi & Moa = New Zealand, Ostrich = Africa,
Elephant Bird = Madagascar, Rhea = South America), then it seems to me
that the likeliest scenario is not that birds originated in the Northern
supercontinent Laurasia, without leaving there any early fossils or living
relatives, and then ratite and penguin ancestors flew down to Gondwana
across the Tethys Sea, distributed themselves all across Gondwana
(including far Western Gondwana - New Zealand's Kiwi and Moa) and
then all became flightless.

It seems to me that a more parsimonious and hence likely scenario, which I
here put forward on CED as a Gondwanan origin of birds theory, is that: 1.
birds originated in Gondwana, probably in Antarctica before Gondwana
started breaking up ~200 mya (see
http://pubs.usgs.gov/publications/text/historical.html); 2. penguin and ratite
ancestors became flightless in Antarctica and the latter walked to South
America, Africa, Australia and New Zealand, which were then all joined; 3.
Africa separated first from Gondwana ~130 mya with its non-flying ratites
and flying birds which had long before already started to fly across the
shortening stretch of Tethys Sea to Europe; 4) South America with flying
and ratite non-flying birds next broke away from Gondwana; 5) South
American flying birds flew across the shortening stretch of sea to North
America.

AFAIK this fits all the facts. I have debated this Gondwanan origin of birds
theory in its early stages with a paleontologist on another list, and although
he didn't agree with me, he produced no facts that falsified my theory. And
at that time I hadn't thought of the penguins as additional supporting
evidence.

If this was the case, then it seems unlikely that Gondwanan Archaeopteryx
and Laurasian dinosaurs are closely related and therefore I assume that the
similarities between them are mainly due to convergence.

And since China was not part of Gondwana, I assume that its `feathered
dinosaurs' being ~120 mya, some are secondarily flightless birds (e.g.
Protarchaeopteryx and Sinosauropteryx) the rest are non-bird dinosaurs
with `feather-like' scales adapted for insulation in China's cold, but not on
the line to birds and therefore feathers.

Of course it is always possible that theropod dinosaurs and birds arose
from the same ancestral stock when Gondwana and Laurasia were
originally joined as Pangaea pre-225 mya, and this together with
convergence would explain the striking similarities between dromaeosaurs
and birds. If birds arose in Antarctica, it would support the theory that
feathers arose from reptile scales as an adaptation for insulation.

I have been meaning to write this up as a Gondwanan origin of birds theory
but haven't had the time. Of course someone else might have already
proposed it as a theory, but I don't know of it. I have other supporting
material, which I will post to CED if this thread continues.

[...]

Steve

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"This phenomenon the separate and independent acquisition of similar
features-is known as 'convergence'. The claim of convergence is the most
important objection to the bird-dinosaur link. Convergence is an extremely
difficult problem. When confronted by two superficially similar organisms,
it is not always easy to spot whether their similarity is a result of shared
common ancestry, or an adaptive response to similar pressures in otherwise
unrelated animals. Ornithologists are very sensitive to this problem,
because many otherwise distantly related birds look deceptively similar
because of a common response to the pressures of flight. In a sense, claims
of convergence are unanswerable, as one can always make a case, based on
adaptation, that any feature thought indicative of common ancestry really
represents a common response to similar adaptive pressures in unrelated
species. Cladistics has a way of addressing the problem: the invocation of
the principle of parsimony. ... Of course, there is no law that says that
evolution is always parsimonious." (Gee H., "In Search of Deep Time:
Beyond the Fossil Record to a New History of Life," The Free Press: New
York, 1999, pp.184-185)
Stephen E. Jones sejones@... or senojes@...
Home: http://members.iinet.net.au/~sejones
Group: http://groups.yahoo.com/group/CreationEvolutionDesign
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