A New Method to Quantitatively Infer the Age Based on Faunal Evolutionary Level

Reliably dating fossil sites lacking radiometric markers is a fundamental challenge. We present a Monte Carlo probabilistic framework that turns qualitative faunal correlation into a quantitative chronology. The method requires detailed, taxon‑specific knowledge of evolutionary levels. It repeatedly simulates plausible ages and evolutionary scores for a target site within predefined ranges via random sampling, then compares each synthetic assemblage with a dated reference dataset using a consistency function that penalises directional mismatches between age and evolutionary change. After many iterations, we collect the 2% of simulations with the highest consistency probabilities; the distribution of their ages forms the posterior age density of the target site. Applied to the Yunxian hominin locality (China), the method yields a most probable age of 0.986 Ma (95% CI: 0.538–1.611 Ma). The framework can also test any externally proposed age (e.g., from radiometric dating) by calculating its relative probability under the faunal‑evolutionary model, offering an objective measure of consistency between alternative chronologies and the fossil record. This approach bridges qualitative biochronology and numerical dating, providing a powerful, reproducible tool for refining the timescale of mammalian evolution.