Taxonomic description and phylogenetic placement of two new species ofSpalangiopelta(Hymenoptera: Pteromalidae: Ceinae) from Eocene Baltic amber

Abstract

Spalangiopelta is a small genus of chalcid wasps that has received little attention despite the widespread distribution of its extant species. The fossil record of the genus is restricted to a single species from Miocene Dominican amber. We describe two new fossil species, Spalangiopelta darlingi sp. n. and Spalangiopelta semialba sp. n. from Baltic amber. The species can be placed within the extant genus Spalangiopelta based on the distinctly raised hind margin of the mesopleuron. 3D models reconstructed from µCT data were utilized to assist in the descriptions. Furthermore, we provide a key for the females of all currently known Spalangiopelta species. The phylogenetic placement of the fossils within the genus is analyzed using parsimony analysis based on morphological characters. Phylogenetic and functional relevance of two wing characters, admarginal setae and the hyaline break, are discussed. The newly described Baltic amber fossils significantly extend the minimum age of Spalangiopelta to the Upper Eocene.

Impact of increasing morphological information by micro-CT scanning on the phylogenetic placement of Darwin wasps (Hymenoptera, Ichneumonidae) in amber

“…Interestingly, before the micro-CT scanning, most of the inclusions were visible laterally from at least one angle, suggesting that the hidden body aspects, which were mostly dorsal and ventral, were not as significant for improving the phylogenetic placement as we initially thought, at least at a subfamily level. Several studies on other organismic groups did show that micro-CT scanning can reveal significant characteristics which helped in the taxonomic placement of fossil species (Garwood et al, 2017 ; Henderickx et al, 2013 ; Moser et al, 2021 ), but to our knowledge, none of them compared the phylogenetic placement before and after the scanning.…”

“…Morphological information revealed by micro-CT scanning can improve and enrich species descriptions (Henderickx et al, 2013 ; Kundrata et al, 2020 ), or it can be used in a phylogenetic analysis to infer the position of a fossil taxon relative to other fossil or to extant taxa. The latter has been done in morphology-only analyses (e.g., Garwood et al 2017 ; Klopfstein & Spasojevic, 2019 ; Moser et al, 2021 ) as well as in combined-evidence analyses (Fikáček et al, 2020 ; Qvarnström et al, 2021 ; Spasojevic et al, 2021 ), where molecular data are used to stabilize the relationships among extant taxa. If the phylogenetic analyses are conducted in a Bayesian framework, then phylogenetic uncertainty is accounted for, which allows for a more objective consideration of fossil placement (Klopfstein & Spasojevic, 2019 ).…”