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Re: Fossil Discovery Threatens Theory of Birds' Evolution
In a message dated 6/26/00 2:22:05 PM, email@example.com writes:
<< >Um... I didn't say that either, and the term is "graptolite". And what
>graptolites supposed to be convergent to?>>
>Okay, it's a thingie that was found near New Guinea a decade or so back.
>There was a possibility of a ghost lineage of four hundred million years if
>it wasn't convergance.
The specific find you refer to was made off New Caledonia, and was
described by Noel Dilly. It is a member of the group of hemichordates
(acorn worms) known as pterobranchs. These are colonial animals very
similar to what we know of graptolites; in fact Dr. Dilly (and others) are
convinced that the two groups are closely related if not actually
identical. The chief functional difference was that individual graptolites
produced a long spine called a nema projecting fron their locations in the
colony, but pterobranchs did not and, it was thought, were incapable of
doing so. However, the new find was of a species, , that did produce a nema.
Dr. Dilly announced this find as
a "living graptolite", but he was speaking structurally rather than
phylogenetically; C. graptolitoides is not the only species in its genus,
and the others do not produce nemas. In effect he was arguing that there
was now no reason to separate the two groups.
Once again, the "convergence" here is related to a single feature among
closely-related animals, and is therefore not equivalent to the extensive
multi-character convergences that would be necessary if theropods were
polyphyletic (in particular if one of the lines you propose was closer to
Longisquama than thjan to other theropods). >>
Closely related? The graptolites went extinct during the Devonian.
Cephalodiscus graptolitoides is Quarternary. The time difference is immense.
Even if either you or I am right in this debate, the fact still remains that
Logismama(sic) and any dinosaur are a thousand times more closely related
than graptolites and Cephalodiscus graptolitoides.