Re: From S. Turner: conodont debate

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[Susan Turner wrote:]

|I would be interested in peoples' response to the idea currently getting
|a lot of media coverage i.e. that conodonts are vertebrates and our
|earliest 'ancestors', and not only that but they exhibit features of a
|predatory lifestyle and have advanced gnathostome characters including
|the presence of 'enamel' on their "teeth". As I have been attempting to
|provide a forum for debate on this in Ichthyolith Issues, and as one of
|the world's leading authorities on early vertebrates, Dr Phil Janvier,
|has now come out in favour of the theory, I think it is time for all
|vertebrate workers and conodont workers to stand up and be counted and
|really get to grips with the meat of the arguments being put forward by
|Dick Aldridge, Mark Purnell, Ivan sansom, paul Smith and Moya Smith.
|There are already several papers out and more in press refuting their
|arguments and interpretations but these do not hit the media because they
|are not so "sexy". So, what do the community think.

	Well, I'll say a couple of things, although I will not hesitate to  
also say my experience with conodonts is limited.

	1.) I think the evidence is quite convincing that conodonts are  
chordates, and that they possess many features also found in vertebrates  
-- for example, phosphatized "hard parts", "bone-like" microstructures,  
cephalization, and development of large eyes.

	2.) Despite the similarities to vertebrates, and even indications   
of gnathosome-like functionality for the conodont apparatus, it is still  
unique.  There are no modern or extinct vertebrates or other chordates  
with a similar structure for food capture and/or processing.  The  
accretionary growth of conodonts on their exterior surface throughout  
their life is also fairly unique.  Most (all?) modern vertebrate teeth  
either grow basally or are shed after being erupted from internal  
development.

	In my opinion, the combination of number 1 (vertebrate-like  
features) and number 2 (unique food-gathering apparatus and growth)  
implies that whether or not condonts are "vertebrates" (and by whatever  
definition you choose), they are a fairly distinct lineage.  Whether this  
lineage is considered "vertebrate" or not is an independent question.  I  
think they are, but, frankly, I do not think this is all that interesting.   
*What* they are, what they did, and how they are related to other  
chordates is more interesting than than just placing them in a category.  


	At the present time I think it is premature to say they are  
ancestral to other groups.  They just seem too unique.  However, they do  
possess features that could be transitional to later vertebrates.  They  
could be demonstrating how the transition occurred, rather than actually  
being the transition.  There are plenty of interesting hypotheses to test.   
Aldridge, Purnell, and others are doing some really interesting work.



	-Andrew
	macrae@geo.ucalgary.ca
	home page: "http://geo.ucalgary.ca/~macrae/current_projects.html";