Ecological drivers and evolutionary patterns: diet, feeding, evolution and extinction in conodonts

Conodonts are a group of extinct jawless early vertebrates. They have one of the most abundant and temporally well resolved fossil records, spanning over 300 million years. While their evolutionary significance is well recognised, little is known about their ecology. This is largely due to the absence of extant animals with homologous feeding tools to compare them with. In this thesis, we review previous research into the feeding function and dietary ecology of conodont elements, critically evaluating the analytical power of the methods used. We demonstrate that a new suite of methods, dental topographic metrics, can successfully infer diet between distantly related clades with nonhomologous feeding tools. Application of dental topographic metrics and consideration of biophysical scaling constraints demonstrates that conodont consumer niche breadth was comparable to modern mammals. Conodont dietary niche was found to be closely associated with descriptive morphofunctional categories, grouping them into dietary guilds. Variation in the relative abundance of dietary guilds throughout their fossil record shows a succession of three distinct faunas, a rapid origination of different ecologies in the Great Ordovician Biodiversification Event, an ecological Devonian Nekton Revolution and little change in ecosystem structure at mass extinction events. High temporal- and ecological resolution analysis of the Hangenberg Crisis extinction event demonstrates that little overall change in ecology across the event was brought about through the selective extinction of hard diets and rapid origination of similar ecologies in the immediate recovery period. This thesis represents a marked change in our understanding of conodont diets. Through the development and application of dental topographic metrics we have unlocked the conodont fossil record for palaeoecological study with an emphasis on diet. We anticipate this to be a starting point for more sophisticated analyses of marine ecosystem structure through time, not only using conodonts but also through the analysis of other enigmatic fossil records.