Re: Conodont elements

[Mark Purnell <map2@xxxxxxxxxxxxxxx>]

In response to Sue Turner's posting:
I am not sure of the relevance of who or how many people at the 
Gross Symposium (more than two years ago) accepted the evidence 
that was available at that time.  The same goes for the rather 
heated letters in Ichthyolith Issues (which mostly predate even the 
Gross Symposium if I remember rightly).  Things have moved on; 
there is new evidence (anatomical, histological and functional) to 
consider and that, if I am not mistaken, is what this debate is 
about.

>There are many other ideas about what the elements are - as people 
>who have read around must know - the main problem being that they 
>were tissue covered

There is no evidence that conodonts were tissue covered during use.  
Sure, they must have been embedded in tissue or tissue covered at 
some time (during their growth) but this has no bearing on their 
function (toothlike or otherwise).  Irrespective of conodont 
affinities, we have known enough about conodont anatomy since 1983 
to rule out all but two functional hypotheses.  Either conodonts 
were microphagous, pump suspension-feeding animals, their elements 
covered in ciliated tissue (the hypothesis championed primarily by 
Bob Nicoll), or conodont elements functioned as teeth.  There is 
evidence that apparatus growth rates were insufficient to have 
provided a growing conodont with sufficient food by 
suspension-feeding, but more importantly, tissue covered elements 
in a microphagous animal would not exhibit microwear.  Conodont 
elements exhibit microwear that cannot be post-mortem in origin and 
must, therefore, result from their use in vivo.  The wear on 
conodont elements is very different to the pattern of abrasion 
caused by post-mortem transport (see Broadhead and Driese, Palaios, 
last year); it occurs at points of occlusal contact between 
elements, and is comparable in microscopic detail to the microwear 
that occurs on mammal teeth.  Several microwear specialists who 
have seen the conodont wear have been happy to accept it as such.  
I know of no other means by which distinct polished, striated, and 
pitted facets can be formed on conodont elements, other than by 
their use as teeth.

>When I have time (maybe after the work 
>leading up to IGCP 328s final meeting to be held in Paris in 
>September) I will sit down and look at condoont elements myself 
>and see if I agree with the wear facets or not.

I would be happy to take you through this when we meet at the 
AusCos/Boucot Symposium in July. I know Bob Nicoll (who has looked 
at more than a few conodont elements) is certainly keen that we all 
get together to discuss these things face to face.

>But even I do not have contact
>with the many hundreds of conodont workers in the Pander Society 
>and I would like to hear their opinions.
So would I.  Maybe at AusCos?

MARK



Dr Mark A. Purnell

Department of Geology, University of Leicester
University Road, Leicester LE1 7RH, U.K
tel: 0116 2523629  fax: 0116 2523918