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ZooKeys 130: 239-254 (2011)

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A long-living species of the hydrophiloid beetles:
Helophorus sibiricus from the early Miocene
deposits of Kartashevo (Siberia, Russia)

Martin Fikaéek'’, Alexander Prokin?, Robert B. Angus*

| Department of Entomology, National Museum, Kunratice 1, CZ-148 00 Praha 2, Czech Republic 2 De-

partment of Zoology, Faculty of Science, Charles University in Prague, Vinitnd 7, CZ-128 44 Praha 2, Czech
Republic 3 Voronezh State University, Research-Educational Center “Venevitinovo’, Universitetskaya sq. 1,
Voronezh 394006, Russia 4 Department of Entomology, The Natural History Museum, Cromwell Road, Lon-
don SW7 SBD, UK

Corresponding author: Martin Fikdcek (mfikacek@gmail.com)

Academic editor: D. Shcherbakov | Received 11 April 2011 | Accepted 11 July 2011 | Published 24 September 2011

Citation: Fikatek M, Prokin A, Angus RB (2011) A long-living species of the hydrophiloid beetles: Helophorus sibiricus
from the early Miocene deposits of Kartashevo (Siberia, Russia). In: Shcherbakov DE, Engel MS, Sharkey MJ (Eds)
Advances in the Systematics of Fossil and Modern Insects: Honouring Alexandr Rasnitsyn. ZooKeys 130: 239-254. doi:
10.3897/zookeys. 130.1378

Abstract

The recent hydrophiloid species Helophorus (Gephelophorus) sibiricus (Motschulsky, 1860) is recorded
from the early Miocene deposits of Kartashevo assigned to the Ombinsk Formation. A detailed compari-
son with recent specimens allowed a confident identification of the fossil specimen, which is therefore the
oldest record of a recent species for the Hydrophiloidea. The paleodistribution as well as recent distribu-
tion of the species is summarized, and the relevance of the fossil is discussed. In addition, the complex

geological settings of the Kartashevo area are briefly summarized.

Keywords
Coleoptera, Hydrophiloidea, Helophorus, Miocene, Kartashevo, long-living species, environmental stability

Introduction

The understanding of the evolution of beetles in the late Cenozoic has changed drasti-
cally within recent decades. This concerns especially the Pleistocene beetles preserved
as unmineralized subfossil specimens. Originally, the remains from the Pleistoce-
ne peatbog or asphalt deposits were assigned to extinct species by historical authors

Copyright Martin Fikacek et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

240 Martin Fikdcek et al. / ZooKeys 130: 239-254 (2011)

(e.g. Lomnicki 1894, Grinell 1908, Orchymont 1927, Pierce 1946, 1948, 1949, 1964,
Scudder 1900), supporting the idea of a high evolutionary rate induced by the climate
changes during the Pleistocene. Later, more detailed studies of subfossil specimens
sometimes based even on the study of their well-preserved genitalia revealed that the
majority of Pleistocene subfossil beetles belong to recent species (Elias 2010; for exam-
ples of taxonomic revisions see e.g., Darlington 1938, Angus 1973, 1997a, Miller and
Peck 1979, Doyen and Miller 1980, Miller et al. 1981) and resulted in the Pleistoce-
ne evolutionary stasis paradigm (Coope 1970, 2004). Recent studies of many beetle
groups based on molecular data contradict the results based on the fossil record for
many beetle groups and indicate a high evolutionary rate during the Pleistocene (e.g.,
Ribera and Vogler 2004, Cardoso and Vogler 2005, Goméz-Zurita et al. 2007, Borer
et al. 2010, Ribera and Faille 2010). This disagreement of molecular and fossil results
is interpreted as resulting from fossil data being only available for high latitude areas
(Ribera and Vogler 2004, Abellan et al. 2011).

The presence of recent species in Pleistocene deposits invites the question as to
whether the same might not be the case even in older, Pliocene or Miocene deposits.
Pre-Pleistocene beetle fossils were mostly assigned to extinct species of recent gene-
ra (Scudder 1891, 1900, Handlirsch 1908). However, this traditional view has been
contradicted recently by many molecular studies showing the pre-Pleistocene origin
of various beetle species (e.g., Gdmez-Zurita et al 2007, Sota et al. 2008, Papado-
poulou et al. 2009, Ribera et al. 2010a,b, Stiiben and Astrin 2010). The fossil record
reliably supporting the hypothesis of long-living species is, however, rather scarce so
far (Matthews 1977, Grebennikov 2010, Hérnschemeyer et al. 2010) as most pub-
lished data are based on approximate identification of fragmentary remains only (e.g.,
Matthews 1977, Bennike and Bocher 1990, Matthews et al. 2003).

Representatives of the hydrophiloid genus Helophorus Fabricius, 1775 are frequent-
ly used in the studies of Quaternary beetle communities. The taxonomy as well as
recent distribution of most species is well known due to the studies by the third author
(largely summarized by Angus (1997b)) and Smetana (1985), and reliable species iden-
tification is often possible even without the examination of male genitalia, using the ex-
ternal characters as e.g. sculpture and shape of the pronotum, width of pronotal flanks
and morphology of the elytron. These characters often allow recognition of very similar
sibling species which makes Helophorus one of the best model beetle taxa for evaluating
the changes of beetle faunas during the Pleistocene (e.g. Angus 1973, 1997a, Morgan
1989, Elias 2010). Ca. 45 species of Helophorus were recorded from the latest Pliocene,
Pleistocene and Holocene subfossil deposits so far (Scudder 1890, Morgan and Morgan
1980, Buckland and Buckland 2006), all of them belonging to recent species (the only
exception is 1. rigescens Scudder, 1890 whose revision is impossible as its type specimen
is lost; Fika¢ek, unpubl. data). Four extinct species were described from the late Mio-
cene deposits in Alaska (2 spp.) and southern Germany (2 spp.) by Matthews (1976)
and Heer (1862). No other fossils of the genus are known from older Tertiary deposits.

Detailed examination of a well-preserved Miocene Helophorus fossil from the col-
lection of the Paleontological Institute in Moscow revealed that it may be reliably

A long-living species of the hydrophiloid beetles: Helophorus sibiricus... 241

assigned to the living species 1. sibiricus and represents therefore the oldest record of
recent species for hydrophiloid beetles. The results of the studies of this fossil are sum-
marized within this paper and the relevance of the record is discussed.

We would like to dedicate this contribution to Alexandr P. Rasnitsyn on the oc-
casion of his 75" birthday as our thanks for his outstanding contribution to the pale-
ontology and entomology and his massive support of younger generations of ento-
mologists and paleontologists all over the world. We wish him many more scientifically
productive years full of good health and cheerfulness!

Geological setting

The geology of the area around Kartashevo village on the right bank of the Irtysh river
(56°06'54"N, 74°41'27"E) is rather complex especially in the eroded parts where two
formations of different age are in contact: the older Abrosimovka Formation and the
overlying Beshcheul Formation.

The Abrosimovka Formation was dated recently by the comparison of its palyno-
logical spectra with the Upper Baygubek Subhorizon of Aral and the North Ustyurt by
Zykin (2009), and its age was considered as upper Oligocene. This was in agreement
with the opinion of Dorofeev (1963) who dated the fossil flora of the Abrosimov-
ka Formation to the upper Oligocene as it retains the basic structure of the Lager-
nosad-Rezhenka floras with many archaic elements. Alternative dating was proposed
by Volkova et al. (2001) who dated the Abrosimovka Horizon to the lower Miocene
(Aquitanian—Burdigalian).

The overlying Beshcheul Formation was dated as middle Miocene by Dorofeev
(1963) due to the similarities of its fossil flora with the Sarmatian floras of the Russian
plain. Middle Miocene was adopted as the age of the formation even in more recent
publications (e.g., Volkova 1982, LePage 2007, Durnikin 2010).

When describing the fossil flora of the Kartashevo region, Dorofeev (1963) re-
cognized five layers in the coastal section of the Irtysh river (listed from deeper parts
towards the current surface): (1) the outputs of lignite, (2) the horizon of the blue-gray,
very dense clay with layers of plant detritus 0-5 m from the water edge (the Karta-
shevo clay stratum), (3) the characteristically stratified suglino-loam of the Beshcheul
Formation with layers of plant detritus ca, between 14—16 m from the water edge, (4)
sand without plant residues, possibly related to the Ishim Formation, and (5) soil and
a thick layer of compost. The fossil specimen refered in this paper was collected from
the exposed Kartashevo clay stratum (i.e., layer 2 sensu Dorofeev (1963)) on the right
bank of the Irtysh River under and just above the water edge (E. K. Sychevskaya, pers.
comm.). The clay stratum was originally assigned to the Abrosimovka Formation and
therefore refered as upper Oligocene in age e.g. by Sukacheva (1982). Recently, it was
found to represent a separate Ombinsk Formation overlying the Abrosimovka Forma-
tion and underlying the Beshcheul Formation in the Kartashevo area. The Ombinsk
Formation is currently dated to the lower Miocene (V.S. Zykin, pers. comm.). The

242 Martin Fikdcek et al. / ZooKeys 130: 239-254 (2011)

samples of spores, pollen and dinocysts from the stratum were analyzed by M. A.
Akhmet ev and N. I. Zaporozhets and confirmed the lower Miocene origin of the stra-
tum (E. K. Sychevskaya, pers. comm.). The Oligocene-Miocene boundary is currently
placed between the Abrosimovka and Ombinsk Formations in western Siberia (Zykin
2009), which also corresponds well with the lower Miocene age of the Kartashevo
clay stratum. Hence, the fossil presented in this paper may be realiably assigned to the
Burdigalian or Aquitalian stages, and approximately dated as 16—23 million years old.
Zykin (2009) mentioned that the climate was relatively stable, moderately warm and
rather humid in the area on the Oligocene-Miocene boundary.

Only one insect species was previously known from the Kartashevo clay stratum
— the caddisfly case described as Terrindusia (s.str.) eugeniae Sukatcheva, 1982 (origi-
nally assigned to the Abrosimovka Formation by Sukatcheva (1982) as the Ombinsk
Formation was not recognized at that time). Besides the Helophorus fossil described in
detail within this paper, there is also another fragmentary fossil from this stratum (PIN
3285/6) which may belong to the hydrophilid genera Hydrochara Berthold, 1827,
Hydrobiomorpha Blackburn, 1888 or Brownephilus Mouchamps, 1959 based on pre-
served morphological characters. More detailed identification is not possible and the
fossil is therefore not treated further in this paper.

Material and methods

The fossil specimen presented in this paper was examined in dry condition. Habitus
photographs of both fossil and recent specimens were taken using the Canon D-550
digital camera with attached Canon MP-E65mm f/2.8 1-5X macrolens, drawings were
traced from the photographs along with a simultaneous check of the fossil specimen.
Scaning electron micrographs of fossil as well as recent specimens were prepared using
the Hitachi S-3700N environmental electron microscope in the Department of Ento-
mology, National Museum in Prague. Data on the morphology of recent Helophorus sibi-
ricus are based on the specimens deposited at the Department of Entomology, National
Museum in Prague, and the Natural History Museum in London.

The Pleistocene records of Helophorus sibiricus from Europe were taken from the
BugsCEP database available on-line (Buckland and Buckland 2006; data file updated
on 18th January 2011), data on records in Siberia and North America were taken
from the published papers (Morgan and Morgan 1980, Garry et al. 1990, Andreev et
al. 2004, Sher et al. 2005, Elias et al. 2006). Published Holocene subfossil records are
not considered in this paper and are also omitted in Fig. 10 as they are too recent and
therefore not relevant to the topic of this paper; moreover, they mostly fall into the
recent distribution range of the species. Data on the recent distribution were adopted
from the papers by Angus (1973, 1992), Smetana (1985) and Hansen (2004) and the
species range was slightly adapted according to the unpublished faunistic data known
to the authors.

A long-living species of the hydrophiloid beetles: Helophorus sibiricus... 243

Results

Superfamily Hydrophiloidea
Family Helophoridae

Helophorus (Gephelophorus) sibiricus (Motschulsky, 1860)
http://species-id.net/wiki/Helophorus_(Gephelophorus)_sibiricus

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

Helophorus sibiricus (Motschulsky): transferred to Helophorus by Gemminger & Har-
old (1868).

For complete synonymy see Hansen (1999).

Material examined. PIN 3285/5 (piece and counterpiece): Russia, Omsk regi-
on, 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 Paleontolo-
gical 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, sli-
ghtly 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 stron-
gly constricted behing tentorial pits, gular sutures meeting at one point. Mentum 1.3x
wider than long, bearing a deep median emargination on anterior margin (Fig. 6, see
the arrow). Apical segment of maxillary palpi asymmetrical. Pronotum 1.85x as wide as
long, widest at anterior third bearing five wide longitudinal furrows. Bottom of the gro-
oves without granulation. All intervals bearing a uniform, rather dense granulation, gra-
nules rather weakly delimited, nearly contacting each other; granulation becoming spar-
ser 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.
Elytra with 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. Mesoventrite subtriangular, anapleural sutures nearly straight. Metaventrite wider
than long, metanepisternum ca. 5.2x as long as wide, with a transverse ridge anteriorly.
Abdomen with five ventrites, ventrite 5 without median emargination, finelly denticula-
te on whole posterior margin. Legs rather long and slender, protarsi with five tarsomeres.

244 Martin Fikdcek et al. / ZooKeys 130: 239-254 (2011)

eae |
rs
bie

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Figures 1-2. Helophorus sibiricus (Motschulsky, 1860), photo of the early Miocene fossil No. PIN
3285/5 from Kartashevo I piece 2 counterpiece.

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,
H. (G.) 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 H. auriculatus), alternate elytral intervals evenly elevated throughout
(bearing only isolated elevate tubercles in H. auriculatus), and completely and dense-
ly granulate pronotal intervals (internal and median interval nearly lacking granules
in H. auriculatus). Besides, the fossil corresponds with the recent H. sibiricus also in
other preserved characters: (1) scutellar stria present and very long [absent in several
subgenera, extremelly long especially in H. sibiricus]; (2) mentum 1.3x wider than long
[more than 1.5x as wide as long in Rhopalohelophorus Kuwert, 1886, Helophorus s.str.,
and Lihelophorus Zaitzev, 1908]. The shape of gular sutures is sexually dimorphic in H.
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.

A long-living species of the hydrophiloid beetles: Helophorus sibiricus... 245

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Figures 3-4. Helophorus sibiricus (Motschulsky, 1860), drawings of the early Miocene fossil No. PIN
3285/5 from Kartashevo 3 piece 4 counterpiece. Abbreviations: mp4 maxillary palpomere 4, clyp cl-

ypeus, fr frons, ics intercalary stria, mt mentum, scut mesoscutellum, aps anapleural sutures of mesotho-
rax, mtv metaventrite, avl abdominal ventrite 1.

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 corre-
sponds 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 H. sibiricus on the Taymyr peninsula is unknown, the nor-
thernmost record known to us comes from the environs of Norilsk (S. K. Ryndevich,
pers. comm. 2011). In North America, 1. sibiricus only occurs west of the delta of Ma-
ckenzie river and does not reach further east even though both taiga and tundra biomes

246 Martin Fikdcek et al. / ZooKeys 130: 239-254 (2011)

Figures 5-9. Helophorus sibiricus (Motschulsky, 1860) 5 habitus of a recent specimen (Mongolia, Baga-
Tenger, coll. National Museum, Prague) 6—7 detail of mentum, the arrow indicates a characteristic emar-
gination on the anterior margin of mentum (6 fossil specimen, SEM micrograph 7 recent specimen, view
from inside) 8=9 detail granulation of head and pronotum, SEM micrographs (8 recent specimen 9 fossil

specimen).

A long-living species of the hydrophiloid beetles: Helophorus sibiricus... 247

o° 30° 60° 90° 150° 180° -150° -120° -90° -60°
@ Kartashevo @ Upper Pliocene and 3 recent distribution
(lower Miocene) Pleistocene records

Figure 10. Fossil and recent distribution of Helophorus sibiricus (Motschulsky, 1860). Subfossil Holocene

records omitted.

are present throughout the higher latitudes in Canada. In fossil record, H. 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 H. sibiricus
known so far. The lower Miocene record presented in this paper is situated slightly
south of the recent limit of the range of H. sibiricus.

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

Discussion

The genus Helophorus is currently divided into 11 subgenera whose monophyly and
phylogenetic relationships have not been tested so far. Regardless, its subgroups dif-
fer sharply by their morphological and taxonomic diversity. Most Helophorus subgen-
era consist of few species only, each rather distinct morphologically from the others,
and are traditionally considered as the remnants of ancient divergences (Fika¢ek and

248 Martin Fikdcek et al. / ZooKeys 130: 239-254 (2011)

Angus 2006). On the other hand, a few subgroups (especially the subgenus Rhopalo-
helophorus and parts of the subgenera Helophorus s.str. and Empleurus Hope, 1838)
contain numerous morphologically very uniform species which are sometimes reliably
recognizable by few details of morphology and/or karyotypes only (e.g., Angus 1982,
1984, Angus and Aouad 2009, Angus and Toledo 2010). These groups are intuitively
considered as results of rather recent diversifications (Fikacek and Angus 2006). Helo-
phorus sibiricus represents the first type, as the subgenus Gephelophorus only contains
two easily distinguishable species at present.

The presented early Miocene fossil of Helophorus sibiricus is still too young to be
taken as a proof of the relic character expected for Gephelophorus due to its high mor-
phological difference but low species diversity. In spite of that, it is the first fossil
definitely indicating that at least some small subgenera of Helophorus contain species
of rather ancient origin rather than recently diverged ones. This seems to contradict
the evolutionary scenario proposed for another small and morphologically distinct
subgroup within Helophorus, subgenus Kyphohelophorus Kuwert, 1886, by Matthews
(1976). He studied two extinct species of the subgenus (H. coopei Matthews, 1976
from late Miocene Lava Camp, and H. meighenensis Matthews, 1976 from Meighen
Island, both in Alaska) and considered them to be ancestors of the only recent species
of the subgenus, 1. tuberculatus Gyllenhal, 1808. This would indicate either a quick
anagenetic change or high divergence and extinction rates of the subgenus during the
late Miocene. Recently, Kiselev and Nazarov (2009) recorded H. tuberculatus from the
late Miocene deposits of Ary-Mas (Taymyr Peninsula, western Siberia) and Letyatkin
Cape (north-eastern Siberia). If the identification of these fossils is correct, they would
show that all three Kyphohelophorus species lived at the same time, proposing a scenario
different from Matthews’ (1976) one: all three Kyphohelophorus species may originate
during the Miocene (or earlier) but only H. tuberculatus survived until present. Helo-
phorus sibiricus might fit a similar scenario based on the fossil presented within this
paper.

The Miocene record of Helophorus sibiricus presented in this paper is not the only
pre-Pleistocene record of recent hydrophiloid beetles. Hayashi (2001) and Hayashi et
al. (2003) recorded modern Japanese species Coelostoma stultum Walker, 1858, C. orbi-
culare (Fabricius, 1775), Hydrochara libera (Sharp, 1884), Sternolophus rufipes (Fabrici-
us, 1792) and Regimbartia attenuata (Fabricius, 1801) from the Japanese early Pliocene
(Tsubusagawa Formation) and late Pliocene deposits (Uonuma, Ookui and Oizumi
Formations). Unfortunately, all these taxa were only found as isolated elytra and pro-
nota lacking any species-specific diagnostic characters, and it is therefore impossible to
imply if the fossils really represent recent taxa. Similar uncertainty concerns the late
Miocene records listed by Kiselev and Nazarov (2009), identified as Helophorus tuber-
culatus (mentioned above) and Coelostoma orbiculare, as no details on the morphology
of the fossils are provided. On the other hand, the morphology of the early Miocene
fossil of Hydrophilus cf. pistaceus Castelnau, 1840 was studied in detail by Fikacéek et al.
(2008), but the preserved morphological characters only allowed for its approximate
identification. Although all these records indicate that the Miocene age may not be

A long-living species of the hydrophiloid beetles: Helophorus sibiricus... 249

exceptional for a hydrophiloid species, the early Miocene fossil of Helophorus sibiricus
presented here represent the first hydrophiloid fossil of this age in which the preserved
characters allow a reliable identification. Early Miocene (i.e., ca. 16-23 mya) may be
thus considered as the maximum age of a recent hydrophiloid species known at pre-
sent. In contrast, all well-preserved late Oligocene and older fossils studied by us so far
were found to belong to extinct species (Wedmann 2000, Fikacéek et al. 2010a,b,c).

The habitat as well as climatic requirements of the beetle species are usually con-
sidered stable over the time (Coope 2004, Elias 2007, Hérnschemeyer et al. 2010),
which provides three possible ways to explain the survival of these species since the
Tertiary: (1) life-style of the species is associated with a habitat which is stable over the
time, (2) the species was able to track suitable environmental conditions though the
climate changed over the time; (3) the species is surviving in a single area with stable en-
vironmental conditions over several millions of years. Although the generalized aquatic
life-style makes the habitat-based explanation seemingly improbable for Helophorus
sibiricus, the occurrence of the notostracan “living fossils” in temporary pools (Manto-
vani et al. 2004) indicates that this kind of waters may provide stable conditions over a
geological time for taxa adapted for their seasonality. Helophorus sibiricus is also able to
track suitable environmental conditions when climate is changing: its distribution was
largely affected by the Pleistocene climate changes even though it presently inhabits an
area with wide range of climatic conditions (mean January temperature below —2°C,
mean July temperature varying between 3—-14°C; S. Elias, pers. comm.). The survival
of H. sibiricus in the long-lasting stable environment in south-western Siberia cannot
be excluded either as the environment in many parts of Central Asia was shown to
remain extremely stable at least since the Pleistocene (e.g., Chytry et al. 2010). The
early Miocene is characterized by the formation of the first stable grasslands alternating
with coniferous-small leaved forests in south-western Siberia (Velichko and Spasskaya
2002), which may correspond with the recent environment inhabited by 1. sibiricus
in the southern part of its range. Hence, we cannot exclude that some locally limited
ecosystems of south-western Siberia might have been stable enough since the late Ter-
tiary, allowing the survival of H. sibiricus and other Tertiary species.

Acknowledgements

We are indebted to several colleagues who provided us with their unpublished data and
comments relevant to the present paper: S. K. Ryndevich (Baranovichi State Univer-
sity, Belarus) for the notes on the recent distribution of H. sibiricus, E. K. Sychevskaya
(Paleontological Institute of the Russian Academy of Sciences, Moscow, Russia) for
the details of the collecting circumstances and comments on the recent understanding
of the geology of the Kartashevo area, A. G. Ponomarenko, D. E. Shcherbakov and A.
P. Rasnitsyn (Paleontological Institute of the Russian Academy of Sciences, Moscow,
Russia) for their continuous support of the work by MF and AP on the hydrophiloid
fossil record and valuable help with the literature and understanding the geology of the

250 Martin Fikdcéek et al. / ZooKeys 130: 239-254 (2011)

Kartashevo area, and D.V. Vasilenko (Paleontological Institute of the Russian Academy
of Sciences, Moscow, Russia) for his help with the literature and valuable discussions
on the geology and stratigraphy of Western Siberia.

The study was supported by grant KJB301110901 from the Czech Academy of
Sciences (GAAV), grant MK 00002327201 from the Ministry of Culture of the Czech
Republic, grant MSM 0021620828 from the Ministry of Education of the Czech
Republic, and grant 11-04-90798 from the Russian Foundation for Basic Research.

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