Introduction
False blister beetles (Oedemeridae) are a cosmopolitan group of beetles classified within superfamily Tenebrionoidea (Lawrence and Ślipiński, Reference Lawrence, Ślipiński, Leschen and Beutel2010). Up to now, ~1500 species have been described, with the most diverse fauna in Oriental and Neotropical Realms (Vázquez, Reference Vázquez1993; Švihla, Reference Švihla, Löbl and Smetana2008; Lawrence and Ślipiński, Reference Lawrence, Ślipiński, Leschen and Beutel2010). Adult oedemerids are known as pollen and nectar feeders and frequently can be observed on flowers. While most of the temperate zone fauna is diurnal in activity, most of the tropical species are nocturnal (Kubisz, Reference Kubisz2006). Larvae of most of the species are wood borers and inhabit damp, rotten wood. The exception is tribe Oedemerini, whose larvae inhabit stems of herbaceous plants.
Family Oedemeridae is divided into three subfamilies: Polypriinae, Calopodinae, and Oedemerinae (Lawrence, Reference Lawrence2005). Cladistic analysis (Lawrence, Reference Lawrence2005) of a limited morphological dataset of adults reconstructs all subfamilies forming a trichotomy. Molecular dating places the origin of the family in the Early Cretaceous at 103 Ma (McKenna et al., Reference McKenna, Wild, Kanda, Bellamy and Beutel2015), 122 Ma (Zhang et al., Reference Zhang, Che, Li, Liang, Pang, Ślipiński and Zhang2018) or 140 Ma (McKenna et al., Reference McKenna, Shin, Ahrens, Balke and Beza-Beza2019). There are various hypotheses which group of oedemerids is the stem group (Švihla, Reference Švihla1986; Lawrence, Reference Lawrence2005), but subfamily Oedemerinae is considered the most derived. However, McKenna et al. (Reference McKenna, Shin, Ahrens, Balke and Beza-Beza2019), based on transcriptome analyses, reconstructed Oedemera nobilis (Scopoli, Reference Scopoli1763) (the type species of Oedemera Olivier) as the most basal representative of the family Oedemeridae, and as a sister taxon to the clade formed by Ditylus Fischer (Oedemerinae, Ditylini), Pseudolycus Guérin-Méneville (Oedemerinae, Asclerini), and Thelyphassa Pascoe (Oedemerinae, Asclerini).
The fossil record of Oedemeridae is very scarce. Several fossils are known from compressions from Jurassic–Cretaceous of China that originally were assigned to Oedemeridae but nowadays are not considered as oedemerid taxa (Kubisz, Reference Kubisz2006; Peris, Reference Peris2017). Thus the oldest member of the Oedemeridae, Darwinylus marcosi Peris, Reference Peris2017, was described from the Lower Cretaceous Spanish amber (late Albian, 105 Ma) and presumably represents the subfamily Oedemerinae. However, due to missing metatarsi, some authors suggest that the taxonomic position of this taxon should be revised (Batelka et al., Reference Batelka, Engel and Prokop2018). Recently, Vitali and Ellenberger (Reference Vitali and Ellenberger2019) described a representative of the false blister beetles, Sparedrus archaicus Vitali and Ellenberger, from the Upper Cretaceous Myanmar amber (Cenomanian, 99 Ma), which was classified within the subfamily Calopodinae. Subsequently, Vitali and Legalov (Reference Vitali and Legalov2020) added four additional species from the same amber source that were assigned to the fossil genus Ditysparedrus Vitali and Legalov, also placed in the subfamily Calopodinae.
Representatives of Oedemeridae also were found in Eocene Baltic amber by several authors (Berendt, Reference Berendt1845; Helm, Reference Helm1896; Klebs, Reference Klebs1910; Larsson, Reference Larsson1978; Willemstein, Reference Willemstein1987), however, virtually no species have been described. Alekseev et al. (Reference Alekseev, Pollock and Bukejs2019), after examination of the holotype and original description, suggested that Neopolypria nigra Abdullah, Reference Abdullah1964, may be closely related to the extant genus Polypria Chevrolat (tribe Polypriini), thus it would be another representative of false blister beetles in Eocene Baltic amber. However, Alekseev et al. (Reference Alekseev, Pollock and Bukejs2019) placed that taxon as Tenebrionidae incertae sedis without formal transfer to Oedemeridae. Nonetheless, Oedemeridae specimens imbedded in amber are considered very rare. Here, we provide description of the first undoubted Oedemeridae representative from Baltic amber based on a female specimen described as Oedemera (s. str.) girulskii n. sp.
Material and methods
This study is based on a Baltic amber piece that was found in secondary amber deposits in Yantarny of the Sambian Peninsula in the Kaliningrad region (Russia), Prussian Formation “Blue Earth” layers. For opinions about Baltic amber age, history of its deposition, and origin, see supplementary material discussion in Szwedo and Drohojowska (Reference Szwedo and Drohojowska2016) or Wolfe et al. (Reference Wolfe, McKellar, Tappert, Sodhi and Muehlenbachs2016), Grimaldi and Ross (Reference Grimaldi, Ross, Fraser and Sues2017), Kosmowska-Ceranowicz (Reference Kosmowska-Ceranowicz2017), and Stebner (Reference Stebner, Szadziewski, Pytlos and Szwedo2018).
The material was polished manually with emery papers of different grain sizes and subsequently shined with polishing powder. The specimen was examined and photographed with a Leica M205A stereomicroscope with Leica DM 6000 digital camera attached to a Leica Application Suite LAS 3.7. Terminology used in this paper follows Švihla (Reference Švihla1999). Adobe Photoshop CS5 was used to prepare graphics.
Repository and institutional abbreviation
The type specimen examined in this study is deposited in the Museum of Amber Inclusions, Gdańsk, Poland (MAIG).
Systematic paleontology
Family Oedemeridae Latreille, Reference Latreille1810
Subfamily Oedemerinae Latreille, Reference Latreille1810
Tribe Oedemerini Latreille, Reference Latreille1810
Genus Oedemera Olivier, Reference Olivier1789
Type species
Necydalis caerulea Linnaeus, Reference Linnaeus1767; designated by Latreille, Reference Latreille1810 = Oedemera nobilis (Scopoli, Reference Scopoli1763).
Occurrence
The genus Oedemera includes ~80 species distributed in the Palearctic and Oriental realms (Kubisz, Reference Kubisz2006; Švihla, Reference Švihla, Löbl and Smetana2008).
†Oedemera (Oedemera) girulskii new species
Figure 1
Holotype
Female, MAIG no. 6785 (ex. coll. R. Girulski), beetle is included in elongate, oval, transparent, yellow piece of amber, without syninclusions, with several gas vesicles.
Figure 1. Oedemera (Oedemera) girulskii n. sp., from Baltic amber, MAIG 6785. (1) Habitus, dorsal; (2) habitus, ventral; (3) head, dorsal; (4) head, ventral, with magnification of the mandibular apex; (5) spurs on protibia; (6) protibia and protarsus; (7) terminal ventrites of abdomen; (8) terminal antennomere; (9) pretarsal claw of hind leg. gal = galea, lp = labial palp, mand = mandible, mp2–4 = maxillary palpomere 2–4, pt1–5 = protarsomere 1–5, ptb = protibia, sp = spur, stp = stipes.
Diagnosis
No trace of the connection between elytral veins 3 and 4 separates the newly described taxon from the subgenus Oncomera Stephens, where these veins are joined by an additional transverse vein. Moreover, the new specimen's antennal insertions are broadly separated (placed near the inner eye margin), while in Oncomera they are distinctly separated from the inner eye margin and placed much closer to each other. Oedemera (s. str.) girulskii n. sp. can be distinguished easily from extant relatives of the subgenus Oedemera by its distinctly appendiculate pretarsal claws (which is not observed in extant taxa), and its relatively large eyes.
Occurrence
Baltic Sea coast, Yantarny settlement (formerly Palmnicken), Sambian (Samland) Peninsula, Kaliningrad Oblast, Russia. Baltic amber from Eocene “Blue Earth” layers, predominantly Bartonian age (41–37 Ma) (for more details, see Material and methods).
Description
Length 4.76 mm. Without evident traces of coloration, seems to be unicolorous (Fig. 1.1, 1.2). Head elongate (Fig. 1.3), slightly rostrate, covered with large punctures, rugose, across eyes wider than width of pronotum; frons between antennal insertions broad, about as wide as the length of antennomere 1 and wider than distance between inner eye orbits between eyes dorsally; eyes large, prominent, finely faceted, distinctly emargined around the antennal socket, distance in the midlength between eyes larger than width of a single eye, inner eye margins converging anteriorly; temples distinct, shorter than eye length; labrum slightly emargined anteriorly. Mandible bidentate apically (Fig. 1.4). Maxillary palpomeres 2 and 4 sub-equal in length (Fig. 1.4); terminal palpomere narrow, elongate, parallel-sided, with oblique apex. Antennae reaching about two-thirds of elytral length (Fig. 1.1); scape about as long as antennomere 3; pedicel elongate, about twice as long as wide, and about one-third as long as scape; antennomeres 3–10 progressively decreasing in length; antennomere 11 (Fig. 1.8) as long as antennomere 6, distinctly sinuate, with emargination on outer surface in the median part filled with numerous short sensillae.
Pronotum elongate (Fig. 1.1), widest just below anterior margin, with two anterior and one basal depressions; anterior and basal pronotal margins with distinct carinae. Scutellar shield distinct, semicircular. Elytra elongate, leaving two last abdominal segments uncovered, narrowing toward apex from its basal one-seventh, humeral calli well developed, subhumeral vein not confluent with lateral margin, lateral margin of elytron not emargined, sutural margin roundly emargined, elytral apices broadly rounded, without apical spine. Wings present. Supracoxal process of metaventrite exceeding metacoxa in lateral view. Terminal abdominal ventrite distinctly truncate or slightly emargined apically (Fig. 1.7).
Legs slender, protibiae not thickened (Fig. 1.6), pro-, meso-, and metatibiae with two apical spurs of different length (Fig. 1.5), pro- (Fig. 1.6) and mesotarsomere 1 about as long as tarsomeres 2–4 combined, pro- and mesotarsomeres 3 and 4 broadened apically, tarsomere 4 distinctly emargined, metatarsus shorter than metatibia, metatarsomere 1 more than twice as long as tarsomeres 2 and 3 combined; pro- (Fig. 1.6) and pretarsal claws of middle and hind legs (Fig. 1.9) distinctly appendiculate.
Etymology
The species is named after Robert Girulski, gemologist, who collected the examined amber piece.
Remarks
This is the first undoubted oedemerid species described from Baltic amber. Although, occurrence of representatives of false blister beetles was mentioned by previous authors (Berendt, Reference Berendt1845; Helm, Reference Helm1896; Klebs, Reference Klebs1910), their amber collections were probably lost and are not available for study.
Discussion
As noted above, fossil Oedemeridae are rare, however, they have been recognized in Baltic amber by several authors. In this paper, we described for the first time a fossil representative of the genus Oedemera and the first representative of the family Oedemeridae from the Eocene amber deposit.
Oedemera girulskii n. sp. in general appearance resembles modern species of the genus Oedemera. It possesses characters defined by Švihla (Reference Švihla1999) as “primitive” (e.g., short frons, convex eyes, profemora not thickened, subhumeral elytral vein not confluent with lateral elytral margin), but also several “advanced” characters (e.g., strongly emarginate terminal antennomere, supracoxal process extending beyond metacoxae, shortened elytra not covering terminal abdominal segments, and last ventrite in female emarginate). Nonetheless, this mixture of morphological features does not allow assignment of this fossil species to any of the already defined species groups within the genus Oedemera.
Placement of O. girulskii n. sp. in Oedemera is supported by elytra narrowing apically, presence of two apical spurs on protibiae, and elytral veins not transversely connected (transverse connection is present in the subgenus Oncomera Stephens). On the other hand, the presence of appendiculate tarsal claws is a very unusual morphological feature that is neither observed in any extant representatives of the genus nor in the entire tribe Oedemerini (as defined by Švihla, Reference Švihla1986). However, this character is present in another tribe of Oedemerinae-Asclerini, which is more diverse, includes more genera, and is regarded as a more basal lineage (Švihla, Reference Švihla1986), while Oedemerini are more advanced. That may suggest that fossil Oedemera girulskii n. sp. with appendiculate tarsal claws represents a plesiomorphic state, which then evolved into simple, non-appendiculate tarsal claws in extant representatives of the genus.
Acknowledgments
We would like to thank R. Girulski for providing the type specimen. M. Kościesza (Museum and Institute of Zoology, PAS, Warsaw) is acknowledged for providing necessary literature. We also would like to thank two anonymous reviewers and the editors for their constructive comments.
