Helophorus (Gephelophorus) sibiricus (Motschulsky, 1860)

Fikacek, Martin, Prokin, Alexander & Angus, Robert B., 2011, A long-living species of the hydrophiloid beetles: Helophorus sibiricus from the early Miocene deposits of Kartashevo (Siberia, Russia), ZooKeys 130, pp. 239-254 : 242-244

Helophorus (Gephelophorus) sibiricus (Motschulsky, 1860)

Empleurus sibiricus Motschulsky, 1860: 104 - Type locality: recent: Russia, East Siberia, “Tourkinsk” [=Turka] at Lake Baikal.

Helophorus sibiricus (Motschulsky): transferred to Helophorus by Gemminger and Harold (1868).

For complete synonymy see Hansen (1999).

Nomenclature citation.

For complete synonymy see Hansen (1999).

Material examined.

PIN 3285/5 (piece and counterpiece): Russia, Omsk region, Western Siberia, right bank of Irtysh river at Kartashevo village [56°6'54.11"N, 74°41'27.20"E], leg. E. K. Sychevskaya 1966. Ombinsk Formation, early Miocene, ca. 23-16 million years ago. Deposited in the collection of the A.A. Borissiak Paleontological Institute of the Russian Academy of Sciences, Moscow, Russia.

Description of the fossil

(Figs 1-4, 6, 9). Body length 5.76 mm. Head black, with a deeply impressed Y-shaped frontoclypeal suture, basal portion of the groove wide, slightly widened anteriorly. Clypeus with weak remnants of granules only, frons bearing very distinct large setiferous granules isolated by ca. a half of their diameters. Gula strongly constricted behing tentorial pits, gular sutures meeting at one point. Mentum 1.3 × wider than long, bearing a deep median emargination on anterior margin (Fig. 6, see the arrow). Apical segment of maxillary palpi asymmetrical. Pronotum1.85 × as wide as long, widest at anterior third bearing five wide longitudinal furrows. Bottom of the grooves without granulation. All intervals bearing a uniform, rather dense granulation, granules rather weakly delimited, nearly contacting each other; granulation becoming sparser sublaterally, consisting of several isolated granules along pronotal margins (Fig. 9). Lateral margin regularly convex, not excised subbasally, lacking any apparent tooth-like projections. Pronotal flanks moderately wide anteriorly, slightly narrowing posteriad. Elytrawith 8 preserved series of large rounded to subquadratic punctures (lateral series not preserved due to deformation of elytra during fossilization). Intervals bearing fine and small irregular series of punctures. Scutellar stria present, very long, consisting of 9 punctures on both elytra. Alternate elytral intervals elevate into low ridges (preserved as elongate ridges and furrows on the ventral imprint of the counter-piece). Epipleuron with rather narrow inner pubescent portion, ca. as wide or slightly narrower than elytral flanks. Mesoventritesubtriangular, anapleural sutures nearly straight. Metaventritewider than long, metanepisternum ca. 5.2 × as long as wide, with a transverse ridge anteriorly. Abdomenwith five ventrites, ventrite 5 without median emargination, finelly denticulate on whole posterior margin. Legs rather long and slender, protarsi with five tarsomeres.

Species attribution.

The subgenus Gephelophorus Sharp, 1915 to which we assign the fossil is easily recognizable from other Helophorus subgenera by the combination of large body size (4.6-7.0 mm), asymmetrical apical segment of maxillary palpi, elevated alternate elytral intervals, pronotal flanks moderately wide anteriorly and narrowing posteriorly, elytral flanks slightly wider than epipleura. Helophorus sibiricus to which we assign the fossil may be recognized from the only other species of Gephelophorus , Helophorus (Gephelophorus) auriculatus Sharp, 1884, by the continuously curved sides of pronotum not excised behind the anterolateral corners (deeply excised anteriorly and projecting into lateral lobes in Helophorus auriculatus ), alternate elytral intervals evenly elevated throughout (bearing only isolated elevate tubercles in Helophorus auriculatus ), and completely and densely granulate pronotal intervals (internal and median interval nearly lacking granules in Helophorus auriculatus ). Besides, the fossil corresponds with the recent Helophorus sibiricus also in other preserved characters: (1) scutellar stria present and very long [absent in several subgenera, extremelly long especially in Helophorus sibiricus ]; (2) mentum 1.3 × wider than long [more than 1.5 × as wide as long in Rhopalohelophorus Kuwert, 1886, Helophorus s.str., and Lihelophorus Zaitzev, 1908]. The shape of gular sutures is sexually dimorphic in Helophorus sibiricus : the gular sutures are separated throughout in males but meeting in one point in females. Based on this character, we can conclude that the fossil specimen is a female.

Recent and fossil distribution

(Fig. 10). Helophorus sibiricus is at present widely distributed throughout the Holarctic region, from the northern parts of Scandinavia and European Russia through the whole of Siberia and the Russian Far East to Alaska ( Angus 1973, 1992, Hansen 2004, Smetana 1985). Its distribution generally corresponds with the range of taiga biome in Eurasia, but slightly exceeds to the temperate and montane forests and grasslands in northern China, Mongolia and Honshu Island, and to the tundra on the north. The species is also reported from Chinese province of Yunnan on the basis of a single historical specimen without precise locality ( Angus 1995) - this record may represent a relict mountain population or could be based on mislabeled specimen, and needs to be confirmed by additional material. The northern limit of the distribution of Helophorus sibiricus on the Taymyr peninsula is unknown, the northernmost record known to us comes from the environs of Norilsk (S. K. Ryndevich, pers. comm. 2011). In North America, Helophorus sibiricus only occurs west of the delta of Mackenzie river and does not reach further east even though both taiga and tundra biomes are present throughout the higher latitudes in Canada. In fossil record, Helophorus sibiricus is frequently found in the glacial deposits dated back to late (Devensian/Weichselian) or middle Pleistocene (Saalian) in northern and central Europe ( Buckland and Buckland 2006). In North America two known fossil records comes from the late Pleistocene glacial (Wisconsinian) deposits in the Great Lakes area ( Morgan and Morgan 1980: Canada, Scarborough; Garry et al. 1990: USA, Illinois). Four records are known from northern Siberian deposits dated back to last glacial (Weichselian; Mamntovy Khayata, Sher et al. 2005), Eemian interglacial (an island in Laptev Sea, Andreev et al. 2004) and late Pliocene to early Pleistocene (Olyorian suite of Krestovka and Chukochya river, Elias et al. 2006). The lower two findings were the oldest records of Helophorus sibiricus known so far. The lower Miocene record presented in this paper is situated slightly south of the recent limit of the range of Helophorus sibiricus .

Biology.

Aquatic species; it is recorded from various kinds of water bodies predominantly with sandy bottom in southern Yamal Penninsula (northeastern Siberia) (Prokin et al. 2008); Angus (1973) considers it as characteristic for river edges in Scandinavia and mentions that it is frequently found in grassy temporary pools particularly those resulting from melting snow in Siberia. Adults of all Helophorus speciesare detritivorous. Larvae of Helophorus sibiricus are unknown but they may be expected to be terrestrial and predaceous as in most other species of the genus Helophorus ( Angus 1997).