Biogeographic dating of speciation times using

15 Standard models of molecular evolution cannot estimate absolute speciation times alone, 16 and require external calibrations to do so. Because fossil calibration methods rely on the 17 unreliable fossil record, most nodes in the tree of life are dated with poor accuracy. However, 18 many major paleogeographical events are dated, and since biogeographic processes depend 19 on paleogeographical conditions, biogeographic dating may be used as an alternative or 20 complementary method to fossil dating. I demonstrate how a time-stratified biogeographic 21 stochastic process may be used to estimate absolute divergence times by conditioning on 22 dated paleogeographical events. Informed by the current paleogeographical literature, I 23 construct an empirical dispersal graph using 25 areas and 26 epochs for the past 540 Ma 24 of Earth’s history. Simulations indicate biogeographic dating performs well so long as pa25 leogeography imposes constraint on biogeographic character evolution. To gauge whether 26 biogeographic dating may have any practical use, I analyze the well-studied turtle clade (Tes27 tudines) then assess how well biogeographic dating fares compared to heavily fossil-calibrated 28 dating results as reported in the literature. Fossil-free biogeographic dating estimated the 29 age of the most recent common ancestor of extant turtles to be approximately 201 Ma, which 30 is consistent with fossil-based estimates. Accuracy improves further when including a root 31 node fossil calibration. The described model, paleogeographical dispersal graph, and analysis 32 scripts are available for use with RevBayes. 33