The palaeobiology of the panderodontacea and selected other euconodonts

Abstract

The apparatus composition and three-dimensional architecture of the coniform conodont genus Panderodus (Llanvim - Givetian) has been reconstructed. This modelling has led to a re-definition of the species concept within Panderodus, which is now reconstructed as a septimembrate apparatus. Taxonomic revision enables the recognition of twelve distinct species, characterised on gross morphological criteria. Using the Panderodus model, it has been possible to recognise recurrent apparatus styles within other coniform genera. This will provide a basis for future suprageneric classification. Homology between coniform and ramiform-pectiniform apparatuses has enabled the development of a unified locational notation for conodonts. A new functional model is presented, highlighting the close similarities of conodont oral apparatuses with those of the petromyzontids. Investigations into the histology of selected conodont elements have identified the presence of cellular bone, two enamel homologues, and globular cartilage. These provide definitive evidence for the vertebrate origins of conodonts, and revised growth models for elements are presented on the basis of these new observations. Cladistic analysis of the expanded character set places conodonts as a sister-group to the "dentineous" craniates. Dentine is no longer recognised as the primitive vertebrate hard tissue. Previous models of early vertebrate hard tissue development, and their significance in evolutionary studies, needs re-evaluation.