The earliest beetle †Coleopsis archaica (Insecta: Coleoptera) – morphological re-evaluation using Reflectance Transformation Imaging (RTI) and phylogenetic assessment

Abstract

The earliest known fossil beetle †Coleopsis archaica is re-examined using Reflectance Transformation Imaging (RTI). The morphological observations are evaluated with respect to phylogenetic implications and the early evolution of Coleoptera. †Coleopsis archaica belongs to an early Permian branch of beetles, outside a monophyletic unit comprising Coleoptera (in the widest sense) excluding †Tshekardocoleidae. This clade is mainly characterized by a complex of apomorphic features: elytra with epipleura and with a close fit with the posterior body, thus forming a tightly sealed subelytral space. In contrast to this, the elytra of †C. archaica and †Tshekardocoleidae cover the metathorax and abdomen in a loose tent-like manner and posteriorly distinctly surpass the abdominal apex. So far, no synapomorphies of the two taxa from the first half of the Permian have been identified. The very short and transverse pronotum is likely an autapomorphy of †C. archaica. A thorough documentation of the structural features of early beetle fossils should have high priority. RTI is a very promising tool to obtain new and well-founded morphological data, which will allow a thorough phylogenetic evaluation of Permian beetles in future studies. We extended the conventional RTI workflow by focus merging and panoramic stitching, in order to overcome previous limitations. Taxonomic re-arrangements of stem group beetles including †C. archaica were suggested in recent studies by A.G. Kirejtshuk and co-workers. As they are not based on shared derived features they are irrelevant in a phylogenetic and evolutionary context.