Morphometric analysis of taxonomy, evolution, autecology and homology in ozarkodinid conodonts

A rigorous understanding of conodont element morphology is fundamental to virtually every aspect of conodont research, yet the complexity of morphological variation within elements presents a challenge for qualitative approaches. To address this problem, a suite of new morphometric protocols has been developed and applied to two conodont taxa. Analysis of the conodont Ozarkodina excavata has enabled development of a new quantitative methodology to objectively discriminate between morphologically similar elements occupying different positions within the conodont skeleton. The methodology differentiated elements with a success rate comparing favourably to expert discrimination, and has application not only in identifying homology in collections of isolated elements, but also in taxonomy. The hypothesis that '0.' excavata is monospecific has also been tested, and the discovery of significant morphological discontinuities between spatiotemporally separated populations strongly suggests that multiple species are currently accommodated within this taxon. The protocols also have potential to permit repeated and objective identification of biostratigraphically useful morphologies. A natural population of lO.' excavata has been examined, elucidating population structure, survivorship and element and apparatus growth within this taxon at a level of detail exceptional even for conodont studies. Evolutionary and taxonomic hypotheses have been tested in the conodont genus Pterospathodus, using a long, densely and evenly sampled stratigraphic sequence. This has revealed few discontinuities within measured variables through time, highlighting the difficulties of objective taxonomic division of an anagenetic continuum. Apparent directional evolutionary trends are partially confirmed, but analysis is hindered by the inability to identify immature elements and separate ontogenetic and evolutionary change. This study has quantified evolutionary rates in conodonts for the first time. The methods and results presented here have the potential to catalyse comprehensive morphometric analysis of conodonts using these widely applicable protocols and refine the existing qualitative framework around which our understanding of conodont morphology is currently based.