Morphometric analysis of graphoglyptid trace fossils in two dimensions: implications for behavioral evolution in the deep sea

Graphoglyptids are deep-marine trace fossils, often found preserved as casts in positive relief on the base of turbidites. Previous analyses of the behavioral evolution of graphoglyptids suggested they were slowly diversifying, becoming optimized, and getting smaller over time until the Late Cretaceous, when a sudden increase in diversification occurred. This current study quantifies the morphology of approximately 400 different graphoglyptid specimens, ranging in age from the Cambrian to the present, in order to evaluate the behavioral evolutionary interpretations made previously. Results from this study indicate that although some general evolutionary patterns can be discerned, they are not as straightforward as previously reported. Different topological categories of trace fossils represent organisms’ responses to evolutionary pressures in unique ways. While burrow widths of meandering traces were becoming smaller over time, as predicted by previous workers, the burrow widths of the ...