The first detailed morphological treatment of a Cretaceous psocid and the character evolution of Trogiomorpha (Insecta: Psocodea)

While new fossil psocid taxa are described every year, the morphology is generally not studied and documented in sufficient detail, limiting our understanding of the character evolution in this order. A new fossil species of the genus Psyllipsocus from mid-Cretaceous Kachin amber is described and its morphology reconstructed in detail using synchrotron-radiation micro-computed tomography (SR-μ-CT). We present the first cybertype of a Cretaceous fossil psocid. We also describe and discuss the putative evolution of previously unrecognized and underestimated exoskeletal characters for the suborder Trogiomorpha. Additionally, using our new observations, we critically evaluate the phylogeny of Trogiomorpha and the character evolution in this group. We also present a modified character matrix which we analyze using Bayesian inference and parsimony. Based on our results and previous studies we propose monophyletic Trogiomorpha s.l. (incl. †Brachyantennum) and Trogiomorpha s. str. (possibly incl. †Cormopsocidae), the latter comprising Prionoglarididae and monophyletic Spinaprocta. Spinaprocta contain Atropetae and Psyllipsocetae (incl. Psyllipsocus) as sister taxa. Some relationships on the genus level in Trogiomorpha are still strongly disputed and unclear. Here, we synonymize the extinct monotypic genus †Khatangia with Psyllipsocus and discuss the systematic position of †Sinopsyllipsocus, †Parapsyllipsocus, †Empheriopsis and †Concavapsocus. A key for all extinct species of Psyllipsocidae is provided.