Baltostigus substriatus, Jałoszyński & Perkovsky, 2019

Jałoszyński, Paweł & Perkovsky, Evgeny, 2019, The Mastigitae genus † Baltostigus in Upper Eocene Rovno amber (Coleoptera: Staphylinidae: Scydmaeninae), Zootaxa 4661 (3), pp. 594-600 : 595-597

† Baltostigus substriatus sp. n.

( Figs 1–10 )

Type material. Holotype: Late Eocene of Europe , Rovno amber: male; inclusion in a prismatic piece of amber 25 × 13 × 8 mm, collection number L-91, collected 10 km north of Voronki village , Vladimirets District, Rovno Region, Ukraine ( SIZK).

Diagnosis. Each elytron with several incomplete longitudinal rows of punctures, not forming sharply defined impressed striae; antennae indistinctly shorter than body; scape over 1.7 × as long as head and slightly longer than pronotum, nearly 5.6 × as long as antennomere III.

Description. Body ( Figs 1–10 ) relatively stout, dark brown, glossy, BL 3.83 mm; vestiture on head, pronotum and elytra inconspicuous, very sparse, composed of very short, suberect setae.

Head ( Figs 3–7, 9 ) elongate, only partly exposed and only in lateral view, HL 0.58 mm; eyes large, nearly circular, strongly convex, moderately finely faceted. Maxillary palp ( Fig. 4 ) typical of Baltostigini , with strongly enlarged and transverse palpomere IV. Punctures on frons and vertex ( Fig. 9 ) sparse but deep and sharply marked. Antennae ( Figs 1, 3–4 ) indistinctly (0.95 ×) shorter than body, AnL 3.63 mm, relative lengths of antennomeres (the shortest antennomere III as 1): 5.57: 3.43: 1.00: 1.86: 1.43: 1.43: 1.36: 1.36: 1.14: 1.07: 1.07. Scape 1.70 × as long as head and 1.15 × as long as pronotum, with five pairs of long ventral spines; pedicel with four pairs of similar spines; basic vestiture of all antennomeres relatively long, moderately dense and recumbent to suberect, all antennomeres additionally with a few long and erect setae.

Pronotum ( Figs 3–7, 9 ) elongate and broadest near anterior third, PL 0.85 mm; disc convex, slightly constricted behind middle, covered with distinct, sharply marked, deep and unevenly distributed punctures ( Figs 7, 9 ).

Elytra ( Figs 1–2 , 5–8, 9 ) much broader than pronotum, strongly convex, broadest slightly behind middle, EL 2.40 mm; each elytron with strong, well-defined punctures forming several incomplete and weakly impressed striae, only adsutural and admarginal rows are complete, possibly also adhumeral row is complete or only slightly irregular (obscured by a milky cloud); humeral calli prominent and short.

Legs ( Figs 1–4 ) long and slender, unmodified.

Hind wings present, left wing protruding from under elytra.

Female. unknown.

Etymology. The name substriatus refers to the distinct, but only partial and incomplete elytral rows of punctures.

Remarks. The specimen can be recognized as a male on the basis of (slightly obscured by a milky cloud) symmetrical apices of parameres visible at the tip of abdomen.

Baltostigus substriatus clearly differs from B. striatipennis in incomplete and weakly impressed rows of punctures on the elytra, which are regular, deep and sharply marked in the latter species. The male of Baltostigus substriatus differs from that of B. antennatus in a larger body ( BL 3.83 mm vs. 3.40 mm B. antennatus ), the scape much longer in relation to the head (ScL/HL 1.70 vs. 1.33 B. antennatus ), a much smaller relative length of scape (length of anI/anIII 5.57 vs. 7.20 in B. antennatus ), and a larger eye. The holotype of B. horribilis is of unknown sex; it is however indistinctly smaller than the male of B. substriatus ( BL in B. horribilis 3.78 mm vs. 3.83 in B. substriatus ), but has proportionally longer antennae (AnL/ BL in B. horribilis 1.09 vs. 1.70 in B. substriatus ). This is an indication that the newly described specimen does not represent a male, and B. horribilis a female, of the same species. Females in Mastigini, the closest relatives of Baltostigini , are always markedly larger than males, but they have proportionally shorter antennae (i.e., the ratio AnL/ BL); this is also a common phenomenon among many other Scydmaeninae. † Baltostigus substriatus differs from B. horribilis in the scape much shorter in relation to the pronotum (ScL/ PL in B. substriatus 1.15 vs. 1.58 in B. horribilis ), whereas the ratio ScL/HL is comparable in both species; and in the scape much shorter in relation to the antennomere III (length anI/anIII equals 5.57 in B. substriatus vs. 7.00 in B. horribilis ). Detailed comparison of measurements of all currently known species of † Baltostigus (and undetermined specimens recorded below as B. cf. horribilis ) are compiled in Table 1–3 .

The specimen of B. substriatus , originally in a larger piece of amber (16 g after polishing), was accompanied by a liverwort, numerous springtails and fragments of ant bodies; there is also a large pocket containing soil in the specimen with the scydmaenine beetle. As the liverwort belongs to an epiphytic group (Mamontov et al. in press), it is possible that Baltostigus was captured in resin on the trunk of a tree. Extant Mastigini, close relatives of Bal- tostigini, climb trees and can even be found over 2 m above the ground (Jałoszyński 2018). Baltostigus might have had similar habits, as the holotype specimen of B. substriatus was caught in resin either at the foot of a tree or on its trunk, among epiphytic liverworts.

Figures

FIGURES 1–4. Baltostigus substriatus sp. n. Lateral habitus (1), pterothorax and abdomen in lateroventral view (2), head and prothorax in lateral view (3, 4).

FIGURES 5–10. Baltostigus substriatus sp. n. Dorsolateral habitus (5, 6), prothorax and head in dorsolateral view (7, 9), elytra in dorsolateral view (8, 10).