Fossil calibrations for the cockroach phylogeny (Insecta, Dictyoptera, Blattodea), comments on the use of wings for their identification, and a redescription of the oldest Blaberidae

Abstract

Here we provide the first thorough assessment of the fossil calibrations for divergence time estimation of cockroaches. Through a review of published fossil descriptions, we evaluate oldest fossils for various nodes in crown Blattodea in accordance with recently proposed best practices. Since most descriptions of fossil cockroaches rely heavily on wing and tegminal venation, we also provide a critical assessment of Rehn (1951), which is the most extensive work on these characters. We find that Rehn (1951) incorrectly reported the state of numerous characters. This, combined with the low number of informative characters in cockroach wings, negatively affects phylogenetic justifications of some of the oldest purported fossil cockroaches. We conclude that currently the best fossils to use for calibration of the cockroach tree are: Cretaholocompsa montsecana, “Gyna” obesa, Cariblattoides labandeirai, and Ectobius kohlsi. One of these, “Gyna” obesa, was insufficiently treated in its original description, so we provide a redescription facilitated by high resolution imagery and modern systematic knowledge. We comment on the difficulty of utilizing the so-called fossil roachoids because their position at the base of Dictyoptera is under dispute and cannot be reliably verified. We do not include calibrations for termite lineages.