Coprolite diversity reveals a cryptic ecosystem in an early Tournaisian lake in East Greenland: Implications for ecosystem recovery after the end-Devonian extinction

The early Tournaisian (Carboniferous) stage represents a key episode in the evolution of vertebrates. It follows the end-Devonian Hangenberg extinction event, which led to a major perturbation to both terrestrial and aquatic vertebrate ecosystems, and resulted in a significant restructuring of assemblages. However, few faunal associations of this age have been described, and our understanding of faunal turnover across the Devonian-Carboniferous boundary remains poor. In this paper, we present an analysis of coprolite material from early Tournaisian lacustrine facies at Celsius Bjerg on Ymer Ø in East Greenland, which overlies the world-famous latest Devonian tetrapod-bearing localities. Fifty-five coprolite specimens (defined as a single coprolite or a piece of shale containing coprolites) were analysed using propagation phase-contrast synchrotron microtomography (PPC-SRμCT). Through a study of external morphology, shape and size combined with information about internal structures, we categorise coprolite morphotypes, and interpret their origin. Notably, we identify a greater number of coprolite morphotypes compared to vertebrate taxa known from skeletal material, indicating the existence of a cryptic ecosystem that has not yet been recovered as body fossils. Vertebrate diversity in the immediate aftermath of the late Devonian extinction is inferred to have been higher than expected, and might have included transient faunal elements within an open system, perhaps involving marine basin connections. Our results show that coprolites offer an alternative fossil data source, revealing diversity that is otherwise not always captured by the skeletal record.