Character analysis and descriptions of Eocene sphodrine fossils (Coleoptera, Carabidae) using light microscopy, micro-CT scanning, and 3D imaging

Abstract

Of the 12 specimens of Calathus-like sphodrine beetles presently known from Baltic and Rovno amber deposits, 11 specimens were investigated using light microscopy, micro-CT scanning, and 3D imaging techniques. For the first time, many significant diagnostic characters of the external morphology and male and female genitalia of Eocene Sphodrini were studied in detail. Based on these data, three fossil species are diagnosed and placed in a natural group characterized by a derived pattern in elytral chaetotaxy and microsculpture and therefore the genus Quasicalathus Schmidt & Will, gen. nov. is described to comprise these species. Due to the presence of a styloid right paramere, Quasicalathus gen. nov. is considered a member of the sphodrine “P clade” of Ruiz et al. (2009). However, given the absence of synapomorphies of any species group of the P clade, the systematic position of Quasicalathus gen. nov. within this clade remains unresolved. The Baltic amber species Calathus elpis Ortuño & Arillo, 2009 is redescribed based on additional, fossil, non-holotype material and transferred to Quasicalathus gen. nov. Identification of the additional C. elpis fossil material remains slightly uncertain due to the non-availability of the holotype for direct comparison coupled with doubts regarding the accuracy of certain character states presented in its original description. Two species are newly described: Quasicalathus agonicollis Schmidt & Will, sp. nov., from Baltic amber, and Q. conservans Schmidt & Will, sp. nov., from Rovno amber.