In search of the sister group of the true lice: A systematic review of booklice and their relatives, with an updated checklist of Liposcelididae (Insecta: Psocodea)

The taxonomy, fossil record, phylogeny, and systematic placement of the booklouse family Liposcelididae (Insecta: Psocodea: 'Psocoptera') were reviewed. An apterous specimen from lower Eocene, erroneously identified as Embidopsocus eocenicus Nel et al., 2004 in the literature, is recognized here as an unidentified species of Liposcelis Motschulsky, 1852. It represents the oldest fossil of the genus. Phylogenetic relationships within the family presented in the recent literature were re-analyzed, based on a revised data matrix. The resulting tree was generally in agreement with that originally published, but the most basal dichotomy between the fossil taxon Cretoscelis Grimaldi & Engel, 2006 and the rest of the Liposcelididae was not supported. Monophyly of Liposcelis with respect to Troglotroctes Lienhard, 1996 is highly questionable, but the latter genus is retained because of lack of conclusive evidence. Paraphyly of Psocoptera (i.e., closer relationship between Liposcelididae and parasitic lice) is now well established, based on both morphological and molecular data. Monophyly of Phthiraptera is questionable, but support for the 'Polyphyly of Lice Hypothesis' is still not definitive. A checklist of valid names of all presently recognized Liposcelididae taxa (10 genera, 200 species) is also included with information on their geographical distribution. Because monophyly of the subfamily Embidopsocinae is highly questionable, we list the genera alphabetically without adopting the usual subdivision into two subfamies.