The first record of Brentidae (Coleoptera) in Eocene Rovno amber with description of a new fossil species of Toxorhynchus Scudder, 1893

A new pear-shaped weevil, Toxorhynchus europeoeocenicus Bukejs et Legalov, sp. nov. (Coleoptera: Brentidae: Apioninae), is described from upper Eocene Rovno amber using X-ray microcomputed tomography (μCT). The new fossil species differs from the extinct Toxorhynchus robustus Poinar et Legalov, 2015 (Dominican amber, lower Miocene) in the larger body size, narrower elytral striae, and wider pronotum. It is the first record of the family Brentidae in Rovno amber and the first record of the genus Toxorhynchus in the eastern hemisphere (urn:lsid:zoobank.org:pub:8FB7B299EE75-4556-B4EA-203A3CBED84C).


Introduction
The curculionoid beetles of amber were studied in detail among the Eocene faunas (Legalov, 2020). The largest numbers of new finds were described from Baltic amber (Legalov, 2020). The Rovno amber fauna was studied less intensely. As a result of research of the new materials collected during the last years, 16 species from four families were described (Gratshev and Perkovsky, 2008;Perkovsky, 2008, 2018;Perkovsky, 2009, 2016;Nazarenko et al., 2011;Legalov et al., 2018Legalov et al., , 2019Bukejs and Legalov, 2019a, b). However, some groups known from Baltic amber, e.g. Nemonychidae; Anthribidae: Allandrini, Belidae, Brentidae; Rhynchitidae: Sayrevilleini, Rhynchitini; Curculionidae: Cryptorhynchini, Eugnomini, Rhamphini, etc., have so far not been found in Rovno amber (Alekseev, 2017;Legalov, 2020;Bukejs et al., 2020). The representatives of these groups can be expected in new amber samples. In examined Rovno amber material, a new species belonging to the genus Toxorhynchus of the subfamily Apioninae was discovered and is described here. It is the first record of the family Brentidae in this fossil resin and the first record of the genus Toxorhynchus in the eastern hemisphere.

Material and methods
The material examined is deposited in the collection of the Museum of Amber Inclusions, University of Gdańsk (Poland) [MAIG]. The amber piece was polished by hand, allowing improved views of the included specimen, and was not subjected to any supplemental fixation.
The X-ray micro-CT observations of specimen "6684" [MAIG] were conducted at Daugavpils University, Daugavpils, Latvia (DU), using a Zeiss Xradia 510 Versa system. Scans were performed with a polychromatic X-ray beam at an energy of 40 kV and power of 3 W. Sample-to-detector distance was set to 17.5 mm, and source-to-sample distance was 47.7 mm. Tomographic slices were generated from 3001 rotational steps through a 360 • rotation, using a 4× objective, and the exposure time during each projection was set to 5 s. Acquired images were binned (2 × 2 × 2) giving a voxel size of 4.87 µm. Images were imported into the Dragonfly PRO (ver. 4.1) software platform for interactive segmentation and 3D visualization.
Published by Copernicus Publications on behalf of the Museum für Naturkunde Berlin.

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A. Bukejs and A. A. Legalov: The first record of Brentidae (Coleoptera) in Eocene Rovno amber Observations of the specimens were made using a Nikon SMZ ® 745T stereomicroscope. The photographs were taken using a Canon 70D ® camera with a macro lens (Canon MP-E 65 mm). Extended depth of field at high magnifications was achieved by combining multiple images from a range of focal planes using Helicon Focus ® v. 6.0.18 software.
The morphological terminology used in this paper follows Alonso-Zarazaga (1990) and Lawrence et al. (2010).

Etymology
The specific name is a compound word and combines "Europe" (Europe, where the Rovno amber originates) and "Eocene" (the time of the origin of this species).

Type material
Holotype. 6684 [MAIG] (ex. coll. Jonas Damzen JDC 8542); adult, male. Rather complete beetle (apical metatarsomeres missing) is included in a yellow, transparent amber piece, with dimensions of 68 mm × 33 mm and a maximum thickness of 14 mm. Syninclusions consist of one damaged specimen of Araneae and few small gas vesicles.
Head. Short, 0.4× as long as rostrum length; widened behind eyes; densely covered with rather large punctures, distance between punctures less than diameter of one puncture, interspaces convex. Rostrum distinctly curved, cylindrical, subparallel-sided, slightly widened medially; sparsely covered with fine punctures; about 4× as long as wide basally and medially, 4.9× as long as wide apically, and 1.5× as long as pronotum length; without preocular sulci laterally. Place of antennal insertion not dilated. Antennal scrobes deep. Temples slightly convex, moderately large, about 0.8× as long as eye transverse diameter. Compound eyes rather large, oval, moderately convex, with large facets, about 1.4× as long as wide. Forehead slightly convex, slightly wider than rostrum base width, with dense micropunctation, without large punctures medially. Gular suture single.
Pterothorax. Sutellum small, suboval, 1.1× as long as wide, anterior margin slightly concave, apex widely rounded. Elytra widely ovoid, convex, 1.3× as long as maximum wide, 3.8× as long as pronotum, punctatostriate; humeral calli developed, protruding; anterior margin concave medially, lateral margins subparallel in anterior half, slightly convex medially, and narrowed at apex. Elytral base wider than pronotum, without crenulate or granulate carina. Elytral punctures small, deep, and rather dense, arranged in nine regular striae, distance between strial punctures equal to 1.3-3.1× diameter of puncture (punctation sparser in posterior portion), striae distinct throughout entire length of elytra; elytral stria 10 lacking; intervals strongly convex, covered with secondary micropunctation, distance between striae about 3× diameter of puncture; hairs not condensed on base of elytral interval 3; sutural stria lacking. Meso-and metaventrites densely covered with rather large punctures (as pronotal punctation), distance between punctures less than diameter of one puncture, interspaces between punctures convex. Disc of metaventrite convex, without median tubercle. Metepisternum wide, 3.5× as long as maximum width, with longitudinal row of large punctures medially; lateral margins slightly concave, anterior and posterior margins oblique.

Comparison
Toxorhynchus europeoeocenicus sp. nov. is similar to T. robustus Poinar et Legalov, 2015 from Dominican amber in body shape but differs in the larger body size, narrower elytral striae, and wider pronotum.

Remark
The studied amber beetle shows the combination of characters corresponding to the family Brentidae: gular suture single, antennae straight, abdominal ventrites 1-2 fused and elongate, ventrites 3-4 shortened, ventrites 1-2 and ventrites 3-5 oriented in different planes. The contiguous procoxal cavities, femora not meeting coxae, elongate trochanters, deep antennal scrobes, scape short, not extending to eyes, visible scutellum, and base of elytra without crenulate or granulate carina suggest placement in the subfamily Apioninae. Placement of this specimen in the tribe Apionini is defined on the elytral stria 10 absent, separated mesocoxae, distinct sutures of antennal club, pronotal vestiture centripetal, rostrum laterally lacking preocular sulci, head widened behind eyes, place of antennal insertion not di-lated, antennae inserted in basal one-third of the rostrum, tarsomere 2 slightly longer than wide, and hairs not condensed on the base of the elytral interval 3. The new species belongs to the subtribe Toxorhynchina based on the campaniform pronotum, curved rostrum, elytral base wider than pronotum, tegminal plate apically distinctly notched, and parameres fused to basal piece. The male metaventrite is not tuberculate, and antennae are inserted in basal one-third of the rostrum. This indicates that a new species belongs to the genus Toxorhynchus. This new fossil species is assigned to the Toxorhynchus decoloratum group based on the combination of the following characters: pronotum with weak basal flange, male legs simple, forehead slightly wider than rostrum base width, antennae inserted at distance of forehead greater than width of forehead, elytra without coarser, denser, and paler scales basally and without postscutellar spot of denser scales.
The genus Toxorhynchus was first described from the Florissant Formation, Eocene of the USA (Scudder, 1893). In the recent fauna, it was described as Coelocephalapion Wagner, 1914. Synonymy was established by Legalov (2013). This genus is widely distributed in North and South America: Canada, the USA, Mexico, Belize, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Colombia, Venezuela, Trinidad, Brazil, Bolivia, Argentina, and the West Indies (Kissinger, 1968(Kissinger, , 1974(Kissinger, , 1992(Kissinger, , 1999de Sousa et al., 1999). Fourteen species were described from lower Miocene Dominican amber, and six of them belong to the Toxorhynchus decoloratum group. The schematic distribution of Toxorhynchus including fossil records is mapped in Fig. 5. Toxorhynchus europeoeocenicus sp. nov. from Eocene Rovno amber is the first record of the genus in the eastern hemisphere.
The similarities between Eocene Baltic amber and recent North and South American Curculionoidea have been documented (Zherikhin, 1971;Legalov, 2016Legalov, , 2020Alekseev, 2017). The relationship between Rovno amber and recent North and South American faunas consisted in the discovery of few fossil species (Bukejs and Legalov, 2019a;Legalov et al., 2019) belonging to the tribes Anypotactini and Naupactini which are distributed mainly in Central and South America (Alonso-Zarazaga and Lyal, 1999). The record of the representative of this genus shows that common groups even at the generic level were present in the American and European faunas in the Eocene.
Data availability. All material included in the paper is deposited in the collection of the Museum of Amber Inclusions, University of Gdańsk (Poland) [MAIG], and all data are included in the description. X-ray microtomography volume renderings of the habitus (Bukejs, 2020a), habitus (without legs, Bukejs, 2020b), and aedeagus (Bukejs, 2020c) (Bukejs, 2020c).
Author contributions. AB and AAL designed the study, drafted the manuscript, and contributed to the writing and discussion. AAL performed systematic placement of this fossil specimen.
Competing interests. The authors declare that they have no conflict of interest.