PALAEONTOLOGICAL ASSOCIATION 42nd Annual Meeting University of Portsmouth 16-19 December 1996 ABSTRACTS and PROGRAMME The apparatus architecture of prioniodontids Stephanie Barrett Geology Department, University of Leicester, University Road, Leicester LE1 7RH, UK e-mail:
[email protected] Conodonts are among the most prolific fossils of the Palaeozoic, but it has taken more than 130 years to understand the phylogenetic position of the group, and the form and function of its fossilized feeding apparatus. Prioniodontids were the first conodonts to develop a complex, integrated feeding apparatus. They dominated the early Ordovician radiation of conodonts, before the ozarkodinids and prioniodinids diversified. Until recently the reconstruction of the feeding apparatuses of all three of these important conodont orders relied mainly on natural assemblages of the ozarkodinids. The reliability of this approach is questionable, but in the absence of direct information it served as a working hypothesis. In 1990, fossilized bedding plane assemblages of Promissum pulchrum, a late Ordovician prioniodontid, were described. These were the first natural assemblages to provide information about the architecture of prioniodontid feeding apparatus, and showed significant differences from the ozarkodinid plan. The recent discovery of natural assemblages of Phragmodus inflexus, a mid Ordovician prioniodontid with an apparatus comparable with the ozarkodinid plan, has added new, contradictory evidence. Work is now in progress to try and determine whether the feeding apparatus of Phragmodus or that of Promissum pulchrum is most appropriate for reconstructing the feeding apparatuses of other prioniodontids. This work will assess whether Promissum pulchrum is an atypical prioniodontid, or whether prioniodontids, as currently conceived, are polyphyletic.