Calibrating the chelicerate clock: a paleontological reply to Jeyaprakash and Hoy.

Divergence times inferred for major lineages of Chelicerata (scorpions, spiders, mites, pycnogonids and xiphosurans) in a recent paper on mitochondrial phylogeny by Jeyaprakash and Hoy are compared to the known stratigraphical occurrences of these groups. Erroneous statements concerning fossil date estimates in the original study are corrected. We emphasize that the fossil record of chelicerates is more complete than is sometimes assumed, and that paleontology plays a key role in dating cladogenesis by setting minimum divergence times, which can and do falsify molecular clock estimates where the inferred divergence is substantially younger than the known fossil record. The oldest representatives of each chelicerate order are documented here, together with similar data for the major mite lineages down to family level. Through these, we hope to provide a robust framework and reference points for future molecular systematic studies of this nature.