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Re: Fossil Discovery Threatens Theory of Birds' Evolution



In a message dated 6/26/00 2:22:05 PM, ornstn@home.com writes:

<< >Um... I didn't say that either, and the term is "graptolite".  And what 
are
>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.

eric l.