BRUNKE, Jałoszyński & Brunke & Yamamoto & Takahashi, 2018

BRUNKE SP. NOV.

( FIG. 7A–J)

urn:lsid:zoobank.org:act:9209EBD8-D459-46E8-9108-7BC08F2E55CE

Type material

Holotype ( CCHH 835-3 ), from Baltic amber ( Russia, Kaliningrad); female (confirmed by μCT scan of postabdomen), preserved in a rectangular prism (7 × 6 × 3.5 mm) of amber ( CCHH / SDEI).

Diagnosis

Protrochanter of female subtriangular, with apical bristle and single apical seta as long as trochanter; elytral index <1.7; pronotum strongly elongate, pronotal index nearly 1.3; scape nearly 3.7 times as long as pedicel, each of antennomeres 4–7 at least 1.25× as long as scape.

Description

Body ( Fig. 7A, E–G) slender, length 3.08 mm, dark brown. Head ( Fig. 7B, H, I) strongly transverse, length 0.45 mm, width 0.58 mm; occipital constriction ( Fig. 7I) about half as wide as width of head, vertex strongly transverse, indistinctly impressed medially and anteriorly confluent with strongly transverse frons; eyes large and strongly projecting from the silhouette of the head; postgenal process ( Fig. 7B, E, F, I) nearly 3× as long as broad, with two long and divergent apical bristles. Submentum ( Fig. 7I) strongly transverse, demarcated laterally by weakly sinuate and complete hypostomal ridges. Maxillary palp ( Fig. 7B, I) much longer than head, palpomere 2 much longer than 3 but shorter than 3 and 4 combined, divided by angulate expansion located in proximal 0.4 into two unequal parts, proximal part distinctly curved, distal part nearly straight and slightly broader, angulate expansion with one robust anterior bristle; palpomere 3 slender, nearly cylindrical in basal half and then gradually broadening distad; palpomere 4 as long as 0.35 of palpomere 3, suboval. Punctures and setae on frons and vertex fine, inconspicuous. Antennae much shorter than body, length 2.26 mm, relative lengths of antennomeres (the shortest antennomere 3 as 1): 4: 1.09: 1.00: 1.45: 1.45: 1.36: 1.36: 1.27: 1.09: 1.09: 1.27. Antennomeres sparsely covered with suberect setae of various lengths. Pronotum ( Fig. 7D, E, G) elongate and broadest distinctly in front of middle, length 0.88 mm, width 0.68 mm, pronotal index 1.29; disc convex and sparsely covered with shallow but distinct punctures (those near middle separated by spaces 2–3 times as wide as diameters of punctures), setae indiscernible; posterior collar demarcated by transverse row of four dorsal pits, additionally one laterodorsal pit located at each side of pronotum; posterior pronotal margin with narrow groove. Prosternum ( Fig. 7F) with basisternal part about as long as procoxae, lacking discernible traces of notosternal sutures, procoxae contiguous. Mesoventral intercoxal process ( Fig. 7J) carinate, parallel-sided, weakly elevated. Metaventrite ( Fig. 7F) slightly impressed posteromedially, metacoxae broadly separated. Elytra ( Fig. 7E, G) strongly convex, broadest near middle, length 1.75 mm, width 1.08 mm, elytral index 1.63; each elytron with four dorsal and two lateral rows of distinct, large punctures; humeral calli prominent, elongate; elytra sparsely covered with short suberect setae. Legs ( Fig. 7A, C, E, F) long and slender, protrochanters ( Fig. 7A, C) elongate and subtriangular, each with moderately long apical spine, extremely long, thin apical seta and 3–4 moderately long, thin subapical setae; profemur ( Fig. 7C) with four long ventral spines, insertions of the first two spines touching each other, additionally profemur with several long and thin ventral setae; protibiae strongly curved; remaining legs unmodified.

Etymology

The name setifer (treated here as a noun in apposition) refers to the unusually long seta on each protrochanter.

Type locality and horizon

Russia, Kaliningrad; Upper Eocene.

Remarks

Apart from the female trochanter, this species differs from the previously known † E. sabathi in the elytral index 1.63 (1.74 in † E. sabathi ), a much more elongate pronotum (pronotal index 1.29 vs. 1.00 in † E. sabathi ), the scape 3.67 times as long as pedicel (only 2.94 times in † E. sabathi ) and each of antennomeres 4–7 at least 1.25 times as long as scape (0.94–1.06 times in † E. sabathi ). In all other characters these two upper Eocene species are very similar.

Results of the μCT scan of † E. setifer demonstrated for the first time that strongly curved protibiae in † Euroleptochromus are not male secondary sexual characters, but occur in females (no traces of the aedeagus were found inside the abdomen). This interesting character is, therefore, the same as in the extant and closely related Leptochromus , in which males and females have curved protibiae, and unlike extinct and extant Mastigini , where this character state is restricted to males of some species. Moreover, the μCT technique revealed structures impossible to observe in the inclusion under light microscopy, e.g. the shape of the hypostomal ridges ( Fig. 7I) or the intermesocoxal region of the mesoventrite ( Fig. 7J).

A very similar specimen (CCHH 835-2, deposited in CCHH/SDEI; Supporting Information, Fig. S6) from the same deposit of Baltic amber (Russian, Kaliningrad) was also studied. It shows some of the diagnostic characters of † E. setifer , i.e. the subtriangular protrochanter with an extremely long apical seta, but it is slightly larger (body length 3.23 mm) and has slightly different proportions of antennomeres, especially the longer scape (4.14× as long as pedicel versus 3.67× in † E. setifer ). This inclusion may represent a separate species, but the opaque, milky amber obscuring the body surface, the position of the beetle inside the amber piece and the partly air-exposed surface make it difficult to measure widths of the pronotum and elytra, important for the diagnosis. This specimen does not add any novel characters to the diagnosis of † Euroleptochromus , but demonstrates a considerable variability in the relative length of the scape and pedicel within the genus.

All these fossils (i.e. the holotypes of † E. sabathi , † E. setifer and specimen CCHH 835-2), as well as † Rovnoleptochromus , have prominent humeral calli (well-visible in Fig. 7E), typical of winged beetles, but hind wings are not observable in any of them. Their closest living relatives, species of Leptochromus , have similarly large and well-defined humeral calli and are winged, suggesting that Eocene species of Leptochromini were capable of flight.