| Abstract: | Goswami, A. & Upchurch, P. (2010). The dating game: a reply to Heads (2010) . —Zoologica Scripta, 39, 406–409. In a recent paper, Heads (2010) argued for the use of continental break‐up dates as calibration points for molecular clocks when the taxon of interest is widely distributed but dispersal across open oceans is considered improbable. Using this method, he estimated that the placental mammal clade Primates originated in the Early Jurassic, requiring a 130 million year ghost lineage before the first euprimate fossils appear in the record. We demonstrate that this argument is flawed for several reasons: 1) Heads's description of the “transmogrification” of fossil calibration dates is inaccurate; 2) the dispersal abilities of primates are not known or estimated in any way; 3) transoceanic barriers can form over long periods, and modern ocean current regimes do not necessarily, or often, reflect past conditions; 4) continental breakup times are more poorly constrained than fossil occurrences; and 5) Heads's descriptions of the mammalian fossil record, the affinities of several fossil mammals, and evolutionary rates are erroneous. While we agree that palaeogeography is a valuable subject for evolutionary studies, the methodology described by Heads is problematic and unlikely to improve the accuracy of divergence time estimates. Consequently, Heads' conclusions concerning primate evolution are unsubstantiated and probably incorrect. |
