The ground beetle genus Bembidion Latreille in Baltic amber: Review of preserved specimens and first 3D reconstruction of endophallic structures using X-ray microscopy (Coleoptera, Carabidae, Bembidiini).

Joachim Schmidt,Peter Michalik

doi:10.3897/zookeys.662.12124

Abstract

The ground beetle genus Bembidion is a highly diverse group of small predators with more than 1.200 described extant species. In contrast, only two representatives of Bembidion are known from the amber fossil record and their position within this mega-diverse genus is dubious. Here, we address the taxonomic position of these two extinct Bembidion species (B. succini Giebel, 1856 and B. christelae Ortuño & Arillo, 2010). Based on the insufficient description and the missing type specimen, B. succini, nomen dubium, cannot be assigned to the genus Bembidion and/or to the tribe Bembidiini with certainty. The subgenus Archaeophilochthus Ortuño & Arillo, 2010 was erected for the second extinct species, B. christelae, based on external characters. However, this species seems indistinguishable to members of the earlier described subgenus Philochthemphanes Netolitzky, 1943 which comprises about extant 10 species distributed in East and Southeast Asia. Furthermore, we describe two new species, B. bukejsi sp. n. and B. alekseevi sp. n., from the Eocene Baltic amber using X-ray microscopy. Based on external and genital morphology including endophallic structures, we erected the monotypic subgenus Eodontium subgen. n. for B. bukejsi sp. n., which is probably related to the subgenera Andrewesa Netolitzky, 1931, the Hydrium complex, or the Odontium series sensu Maddison (2012). On the other hand, B. alekseevi sp. n. can be assigned to the subgenus Eupetedromus Netolitzky, 1911. The occurrence of representatives of at least two species groups adapted to a temperate climate suggests the presence of at least locally temperate climates in Baltic amber forests.

Highlights

Ground beetle fossils of the mega-diverse genus Bembidion preserved in Baltic amber are frequently mentioned in catalogues of amber inclusions (Klebs 1910, BachofenEcht 1949, Larsson 1978, Spahr 1981, Keilbach 1982, Hieke and Pietrzeniuk 1984, Alekseev 2013)
This fossil Bembidion is considered to be a representative of the subgenus Eupetedromus Netolitzky, 1911 based on combination of the following characters: (i) micro-meshes on surface of head and pronotum deeply engraved and contrasting with the elytra which appearing polished when viewed by magnification below x80; (ii) penultimate segment of maxillary palpus rather slender; (iii) anterior supraorbital pore on internal side semicirculary surrounded by a prominent ridge; (iv) supraorbital furrows very shallow; (v) pronotal median longitudinal impression not deepened near base; (vi) pronotal posterior transverse impressions very shallow; (vii) elytral discal setiferous pores distinctly separated from third stria; (viii) distance between third and fourth setae of the umbilical humeral series much larger than between first and second and between second and third setae
At least three species of Bembidion are currently known to occur in the Baltic amber forests, which can be assigned to very different lineages of the genus

Summary

Introduction

Ground beetle fossils of the mega-diverse genus Bembidion preserved in Baltic amber are frequently mentioned in catalogues of amber inclusions (Klebs 1910, BachofenEcht 1949, Larsson 1978, Spahr 1981, Keilbach 1982, Hieke and Pietrzeniuk 1984, Alekseev 2013). A careful examination of the amber fossils preserved at several institutional collections in Germany performed by one of us (J.S.) revealed that previous identification are often erroneous and confused with species of other ground beetles lineages, mainly Tachyina and Trechini, whereas true Bembidion fossils seem very rare inclusions. Alekseev Collection (Kaliningrad) available for a detailed study using light and X-ray microscopy. Both specimens are representatives of hitherto unknown species. We address the taxonomic position and history of the two previously described Bembidion fossils. Based on the habitat preferences of extant Bembidion lineages related to the fossil lineages, we hypothesize some ecological conditions likely present in the Baltic amber forests of the Eocene North Europe

Material and methods

Conclusions