conodont growth etc.

[Mark Purnell <map2@xxxxxxxxxxxxxxx>]

Andrew MacRae makes some sensible points, but perhaps 
overemphasises the apparent uniqueness of conodonts.  It is true 
that no other vertebrates (or chordates) have a feeding apparatus 
the same as that of conodonts, but the key to understanding the 
conodont apparatus is the recognition of its bilateral operation 
across the axis of the animal.  Such bilateral "biting" also occurs 
in Hagfish and Lampreys, but they don't have mineralised feeding 
elements.
Secondly, the way in which conodont elements grew is not as simple 
as much of the literature might suggest.  Continuous external 
apposition of growth lamellae over the entire surface of the 
elements throughout life has long been part of the classic 
arguments for why elements could not have been teeth and conodonts 
could not have been vertebrates.  These arguments and traditional, 
oversimplified models of conodont element ontogeny are no longer 
tenable.
So, may be conodont were not that bizarre after all.
MARK



Dr Mark A. Purnell

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