You Are Where You Live: Using the size of conodont dental tools to shed light on environmental conditions and community complexity

One of the most versatile tools in a palaeontologists’ “tool-kit” is body size analysis, which can be used to characterise and quantify a wide range of ecological and physiological traits.  Utilisation of these data allows insight into predator prey relationships, respiration rates, mortality rates, and even population dynamics. Body size analysis becomes essential when studying extinct organisms where few other clues to their ecology are available. An extreme example of such organisms are conodonts, which are hypothesised to be among the first predators.  Here, changes are tracked  through the Silurian Period using coniform conodont elements as a proxy for body size. Previous research focuses primarily on species turnover, however the data collected in this study is independent of species identification, relying purely on body size changes to reflect the ecology of the community. The size of coniform elements are measured across a number of bathymetries spanning approximately 10 million years. This allows a comparison of body size change not only across differing environments, but also through time. The morphometric measurements were determined using FossilJ, a plugin for ImageJ which facilitates semi-automated measurement of two-dimensional images. Firstly, our results show a clear correlation between body size change and onshore offshore gradients with smaller organisms residing at shallower water depths, unlike what is seen in today’s oceans. Secondly, specimens span across two of the three recorded isotopic excursions during the Silurian Period, the Mulde and Lau events. The impact of these events on conodont communities is represented by a reduction in body size directly after each. Furthermore, the results suggest the Mulde event may have had a stronger effect on these communities and could potentially reflect a time of stress and/or extinction for coniform conodonts.