Spatial Distributional Simulation of Graptolites from the Ordovician Liexi Fauna

The Liexi fauna, found in western Hunan Province in southern China, represents the initial radiation of Ordovician organisms during the mid-Floian age and shows a complex and complete marine ecosystem. Recent investigation of graptolites shows that both benthic and planktic graptolites are present in the Liexi fauna, confirming that its palaeoenvironment represents the transitional zone between the carbonate platform and the upper slope. Dendroids inhabiting these regions are a particularly compelling subject for the study of hydrodynamic control. This makes them an ideal model for understanding how they solve or adapt to physical problems in habitats where they must contend with ambient flows in order to remain balance. In this study, we examined an in-situ preserved dendroid graptolite community containing seven isolated dendroids on the same layer from the Liexi fauna. We then conducted Computational Fluid Dynamics (CFD) simulations on these Ordovician dendroid grapotolites to reveal the possible influence of hydrodynamics on their distribution. Our work first suggests that these dendroids maintain a certain distance from each other. Their spatial distribution is statistically significant and non-random, which would avoid disturbance among individuals. Our CFD simulation results further indicate that this spatial distribution is an effective ecological strategy for producing low-velocity fluids beneficial to the dendroid community. Thus, our work provides new evidence suggesting that hydrodynamic conditions act as a powerful natural selective force in shaping the ecological evolution of marine dendroid graptolites.