Lasconotus tenebrisilvarum Alekseev et Bukejs, 2024

ALEKSEEV, VITALII, MCKELLAR, RYAN C. & BUKEJS, ANDRIS, 2024, A revision and addition to Zopheridae (Coleoptera: Tenebrionoidea) in Baltic amber: possible connections between modern Holarctic distributions and Eocene ‘ amber forests’, Zootaxa 5536 (2), pp. 201-247 : 213-216

Lasconotus tenebrisilvarum Alekseev et Bukejs sp. nov.

( Figs 11–16 )

Type material. Holotype: No. RSKM_PAL_A73 [ RSM] (ex coll. Jonas Damzen JDC-13074 ); “Holotype / Lasconotus tenebrisilvarum sp. nov. / Alekseev et Bukejs des. 2024” [red printed label]; adult, sex unknown . A complete beetle with exposed metathoracic wings is included in a transparent, yellow amber piece with dimensions of 10× 5 mm and a maximum thickness of 5 mm, preserved without supplementary fixation. Syninclusions: one specimen of a phoretic uropod deutonymph (Acari: Mesostigmata : Uropodina ) attached to right side of pronotum.

Type stratum. Baltic amber from Eocene amber-bearing Blaue Erde deposits; estimated age: middle–late Eocene (Standke 1998).

Type locality. Yantarny settlement (formerly Palmnicken ), Sambian (Samland) Peninsula, Kaliningrad Region, Russia.

Description. Measurements: total body length (including visible part of head) 3.5 mm, maximum body width (across elytra) 1.15 mm; head length 0.4 mm, head width (across eyes) 0.8 mm; pronotal length 0.8 mm, maximum pronotal width 1.0 mm, basal pronotal width 1.0 mm; elytral length (along elytral suture, including scutellum) 2.3 mm.

Body subparallel-sided, elongate, about 3.1× as long as wide, weakly convex dorsally and ventrally, unicolorous black (as preserved). Pubescence: head and pronotum with fine, curved setae; elytra sparsely covered with slightly longer, semierect, narrow, uniform setae arranged in rows, and not forming patches.

Head prognathous, transverse; densely granulose dorsally, with granules rather large near center of frons, about 2× as wide as diameter of one eye facet, distance between granules distinctly smaller than diameter of one granule, each granule bearing short, curved, narrow seta. Anterior margin of clypeus widely rounded. Compound eyes large, nearly hemispherical, strongly convex, without interfacetal setation. Frons with strong, complete supraocular carinae. Antennal insertions concealed dorsally. Antennal groove ventrad eye absent. Antennae short, extending to about middle of pronotal length; 11-segmented with distinct, loose, flattened, 3-segmented club; sparsely covered with short, semierect setae; scape and pedicel wide, cylindrical, about 1.5× as long as wide; antennomere 3 conical, slightly dilated apically, about 1.4× longer than antennomere 4, narrower than pedicel; antennomeres 4–8 slightly elongate, subcylindrical to subtrapezoidal, slightly dilated apically, subequal in length; antennomere 9 dilated apically, strongly transverse, 2.2× as wide as long, about 2.0× wider than antennomere 8; antennomere 10 widest, strongly transverse, 2.3× as wide as long, about 1.3× wider than antennomere 9; antennomere 11 widely oval, transverse, about 1.3× as wide as long, distinctly narrower than antennomere 10, finely setose, with widely rounded apex. Maxillary palpi with four palpomeres; palpomere 1 smallest, subtriangular; palpomeres 2 and 3 subquadratic, nearly as long as wide, subequal in size and shape; palpomere 4 elongate oval, truncate, about as long as previous palpomeres combined. Terminal labial palpomere subtriangular, acute apically.

Pronotum slightly transverse, 1.2× as wide as long, widest at base, almost parallel-sided, slightly narrowed anteriad, maximum pronotal width / basal pronotal width = 1.0; pronotal disc weakly convex, with two pairs of sharp, uninterrupted, sublateral carinae; pronotal surface densely covered with granules, bearing curved setae, distance between granules smaller than diameter of one granule. Outer pair of pronotal sublateral carinae subparallel, slightly curved, and almost forming subrectangular area together with anterior and posterior pronotal margins; inner pair of pronotal carinae curved, forming longitudinal oval median area with truncated ends, interrupted anteriorly and posteriorly. Lateral margins finely crenulate, raised, forming distinct longitudinal depression between the lateral margin and first pair of pronotal sublateral carina; anterior pronotal margin arcuate, slightly raised medially; posterior margin rounded. Anterior pronotal angles prominent, acute, slightly rounded; posterior angles almost rectangular and not projecting posteriorly. Prothoracic notosternal suture complete. Hypomera densely and coarsely granulose, distance between granules smaller than diameter of one granule. Prosternum convex; densely covered with small granules. Intercoxal prosternal process elongate, with rounded apex, narrow, about 0.7× as wide as diameter of procoxa, with fine median carina in apical portion, not expanded apically beyond midpoint of procoxa. Procoxal cavities narrowly open posteriorly.

Scutellar shield minute, drop-shaped, slightly transverse, dilated apically.

Elytra almost parallel-sided in anterior two-thirds of their lengths, narrowed in posterior one-third, rounded at apex; about 2.0× as long as wide combined; carinate and convex; 2.8× longer than pronotum. Elytral base slightly wider than pronotal posterior margin. Humeral angles rounded. Elytra striate-punctate. Scutellary striole present. Elytral striae with rows of elongate granules; odd elytral intervals (1, 3, 5, 7) carinate; elytral carinae similarly raised along their entire lengths. Epipleura present, well-developed, widest in basal half, narrowing posteriad, incomplete, apparently reaching abdominal ventrite 5, densely covered with round granules. Mesoventrite convex, densely and coarsely punctate. Mesocoxal cavities closed. Metaventrite with disc almost flat, longer than abdominal ventrite 1, with dense and coarse punctation; discrimen distinct in posterior two-thirds. Relative length ratio of pro- to meso- to metaventrite to abdomen approximately equal to 10:6:11:26. Metathoracic wings present.

Legs rather short and robust, finely punctate and pubescent. Procoxa nearly rounded, narrowly separated by 0.6× diameter of procoxa; mesocoxae hemispherical, narrowly separated by about 0.3× diameter of mesocoxa; metacoxae oval, transverse, separated by 0.5× longitudinal diameter of metacoxa. Femora elongate oval, dilated medially, flattened; femora and tibiae subequal in length. Tibiae straight, dilated apically, with fringe of stout setae and two spines apically. Tarsi slender, about 0.6× as long as tibia; tarsal formula 4-4-4; tarsomeres with sparse, fine setation ventrally; tarsomere 4 longest, longer than metatarsomeres 1–3 combined, widened distally, slightly curved. Claws simple, large, about 0.3× as long as tarsomere 4.

Abdomen with five visible ventrites, abdominal sutures distinct throughout length; densely covered with small punctation. Relative length ratios of ventrites 1–5 equal to 10:5:4:3:3. Abdominal ventrite 1 with small, triangular intercoxal process. Abdominal ventrite 5 with widely rounded apical margin, and with preapical groove.

Differential diagnosis. Lasconotus tenebrisilvarum sp. nov. differs from all extant congeners in the combination of the following characters: elytra convex (in contrast to concave elytra of several North American representatives); elytra with elytral carinae similarly raised along entire lengths; pronotum with two pairs of distinct and uninterrupted sublateral carinae; anterior margin of pronotum without distinctive paired tufts of long, golden setae; raised lateral margin of pronotum forming distinct longitudinal depression between lateral margin and first pair of pronotal carina; pronotal margins almost parallel; posterior pronotal angles almost rectangular and not projecting posteriorly; and elytra at base only slightly wider than pronotum. Additionally, L. tenebrisilvarum sp. nov. differs from the majority of the genus representatives in possessing narrowly open procoxal cavities, a character shared with two North American species, L. fitzgibbonae Kingsolver et al., 2006 , and L. coronatus Hinton, 1935 .

The new species can be easily distinguished from other extinct Colydiinae found in Baltic amber based on the combination of generic characters, most obviously in the presence of 11-segmented antennae with a 3-segmented club, pronotum with two pairs of sublateral carinae, presence of supraocular carina, and carinate elytra.

Derivatio nominis. The name of the new species tenebrisilvarum is derived from the Latin “ tenebricae silvae ” in genitive case, meaning “of dark forests”. This refers to the region of the specimen’s origin in two ways: (1) referring to Eocene forest paleohabitats, and (2) to the former Eastern Prussia, a historical area with the informal anthem “Land der dunklen Wälder“ (land of dark forests), written by Erich Hannighofer and Herbert Brust.

Distribution of congeners. The genus Lasconotus is cosmopolitan, being represented in the New World by 37 species ( Ivie et al. 2016), and in the Palearctic by 8 species ( Ślipiński & Schuh 2008; Aoki 2011, 2018). Only one species, L. jelskii (Wankowicz, 1867) , is known as a primeval forest relict in Eastern and Northern Europe, whereas the most diverse Palearctic fauna has been reported from Japan (4 species: L. akitai Aoki, 2018 ; L. niponius (Lewis, 1879) ; L. okadai Aoki, 2011 ; and L. sculpturatus (Sharp, 1885)) . The fossil species described in the current paper confirms the presence of the genus in the Paleogene Western Palearctic.

The single Recent European species is boreal and the locality in Puszcza Białowieska ( Poland / Belarus), situated at about 52°30´N, is one of the southernmost known points of the group’s present-day distribution ( Nikitsky & Slipinski 2003). Like the situation with fossil erotylid species from Rovno amber, Zavaljus lyubarskyi Alekseev et Bukejs, 2023 ( Alekseev & Bukejs 2023), the southern limit of the present-day distribution range of the genus Lasconotus in Europe almost coincides with the late Eocene record at approximately 51° N. On the other hand, the modern boreal distribution of Lasconotus is evident only for Europe. Representatives of the genus inhabit different latitudes in North America from Canada to Mexico inclusive, and they are also known in different localities in the southern Palearctic (e.g., Central Asia, Nepal, Saudi Arabia, Japan). The present-day boreal distribution of the genus in Europe is probably determined not by climatic reasons and preferences of the genus, but by historical factors related to Quaternary glaciations.

Ecology of congeners. The ecology of representatives of the genus Lasconotus is insufficiently known. Reports from North America, Europe and Asia show association of different species with pinacean conifers ( Pinus and Picea ), where the beetles are noted under bark in the galleries of bark beetles ( Curculionidae : Scolytinae ) belonging to the representatives of genera Ips and Polygraphus ( Saalas 1923; Hackwell 1973; Nikitsky & Slipinski 2003; Kingsolver et al. 2006). Lasconotus larvae of instars 1–2 feed upon fungi, and later (instar 3) they are predaceous on bark beetle larvae ( Hackwell 1973). The Eocene Lasconotus tenebrisilvarum sp. nov. could also be associated with an analogous ancient forest community of dead coniferous trees infested by scolytines. While bark beetles of the genus Ips De Geer, 1775 and tribe Ipini Bedel, 1888 are unknown from inclusions in Baltic amber, the tribe Polygraphini Chapuis, 1869 ( Curculionidae : Scolytinae ) is represented in Baltic amber by two described species of the genus Carphoborus Eichhoff, 1864 ( Legalov 2020, 2024). The trophic association with galleries of these beetles could be assumed for Lasconotus tenebrisilvarum sp. nov.

Figures

FIGURES 11–13. Lasconotus tenebrisilvarum sp. nov., holotype, No. RSKM_PAL_A73 [RSM]: 11—habitus, dorsal view; 12—habitus, ventral view; 13—habitus, right lateral view. Scale bar = 0.5 mm.

FIGURES 14–16. Lasconotus tenebrisilvarum sp. nov., holotype, No. RSKM_PAL_A73 [RSM]: 14— habitus, left lateral view; 15—habitus, frontal view; 16— details of head and thorax, ventral view. Abbreviations: a1–a11—antennomeres 1–11, respectively; pp—prosternal process; tmp—terminal maxillary palpomere. Scale bars = 0.5 mm for Figs 14 and 15; 0.25 mm for Fig. 16.