Reproducing and understanding a fossil trail in digitized worlds: a protocol to quantitative analyses of movement trajectories

Quantitative analyses of trace-fossil trajectories are increasingly applied to infer anatomy, behaviour, sensory capacity, and ecology in extinct organisms, yet methodological standards for this process and related interpretations remain poorly defined. Here we present a general analytical protocol for trajectory-based ichnological studies that explicitly addresses key methodological issues, including trajectory discretization, normalization, choice of signal and sampling frequency, convergence of statistical descriptors, substrate control, and physics- and response-constrained interpretations. We demonstrate that high sampling frequency could introduce unconstrained measurement errors. We find that convergeable metrics are robust and comparable across trails because they primarily reflect intrinsic properties of the trace-maker anatomy and locomotory dynamics. We further show that interpretations involving non-spatial parameters require exceptional caution unless a physically justified constant linking spatial and non-spatial parameters is identified. Finally, we emphasize that geometrically complex traces should not be overinterpreted when they can be parsimoniously explained by stereotyped intrinsic responses such as taxis or kinesis. By formalizing best practices and evaluation criteria, this protocol provides a reproducible methodological foundation for quantitative ichnology and reduces misinterpretation arising from analytical artefacts.