The deposit Ustyanka-1 (Fig. 1) is located on the right bank of the Ustyanka River, right tributary of the Alei River in the Loktyovskii District of the Altaiskii Krai region of Russia, 8 km NNE of Pokrovka Village. The sample with a Malachiidae fragment was taken on 6 August 2013 by E.V. Zinovyev and K.A. Tsepelev from layer 9, section II of the deposit. A description of the section at 51°15'37.4''N, 81°28'57.4''E made by E.V. Zinovyev is as follows:

layer 1, 0.00-0.90 m, humified horizon (chernozem);

layer 2, 0.90-1.85 m, light-beige loamy sand with interlayers and ferruginous lenses;

layer 3, 1.85-1.86 m, interlayer of coarse-grained sand and gravel;

layer 4, 1.86-2.00 m, light-beige loamy sand;

layer 5, 2.00-2.03 m, alternating coarse-grained sand and gravel;

layer 6, 2.03-2.88 m, light-grey loam, dense, with vertical ferruginous striae;

layer 7, 2.88-3.48 m, coarse-grained sand and reddish-brown gravel with grey-green loam with small lenses;

layer 8, 3.48-4.08 m, green-grey loam, dense, with ferruginous spots;

layer 9, 4.08-5.28 m, blue-grey clay with alluvial detritus and insect remains; the layer is partly below the shore line.

Two samples for entomological analysis were obtained from the layer 9, namely: sample 2 at a depth pf 5.00-5.20 m and sample 3 at 4.48-4.70 m.

Other fragments of Malachiidae were extracted on 2 July 2020 by A.A. Gurina, R. Yu, E.R. Dudko and N.N. Golosova, from layer 11 of section I (Fig. 2). A description of the section at 51°15'38.0'' N, 81°28'57.2'' E made by A.A. Gurina and R.Yu Dudko is as follows:

layer 1, 0.00-0.64 m, soil-plant layer;

layer 2, 0.64-1.01 m, light-beige loamy sand;

layer 3, 1.01-1.05 m, interlayer with ferruginous sand and gravel;

layer 4, 1.05-1.75 m, dark-grey loamy sand with ferruginous vertical inclusions;

layer 5, 1.75-2.05 m, interlayer of strongly ferruginous sand and gravel;

layer 6, 2.05-3.49 m, beige loam with ferruginous vertical inclusions;

layer 7, 3.49-3.54 m, light-beige coarse-grained sand;

layer 8, 3.54-3.70 m, light-beige loam with inclusions of shells;

layer 9, 3.70-4.00 m, brown loam;

layer 10, 4.00-4.10 m, interlayer of brown and grey-blue loam with inclusions of plant detritus;

layer 11, 4.10-5.62 m, blue and blue-grey clay with interlayers of dark-grey loam and mollusc shells in the upper portion of the layer and a coarse sand in the lower; alluvial plant detritus and insect remains included; remaining 22 cm of the layer located below the shore line. 32 samples each of 4-6 cm were extracted from layers 10-11 serially.

Sampling methods follow those of Coope (1959) with modifications of Gurina et al. (2019c). The sediment, containing a mixture of plant detritus and insect fragments, was sieved (3 mm meshes) in filtered river water. In the laboratory, the concentrate obtained was washed with tap water and fractioned via meshes of 2 mm, 0.6 mm and 0.3 mm, respectively. The extracted fragments including well preserved malachiids parts were clearly visible on the sieve; these were air dried, and the insect fragments were selectively removed under a binocular microscope Carl Zeiss Stemi 2000. After washing first with “Sanelit” synthetic detergent, then with running water with the aid of a syringe, the fragments were mounted with water-soluble glue onto entomological boards. Each numbered fragment was into a digital database, and the specimens deposited in the collection in the Institute of Systematics and Ecology of Animals, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia.

Four radiocarbon dates were obtained for the basal layer (blue-grey clays) of the Ustyanka-1 site. Two of these 10150±200 ¹⁴C BP (SPb-1345) and 10806±100 ¹⁴C BP (SPb-1346), using liquid scintillation counting for measuring ¹⁴C activity, were undertaken by M.A. Kul’kova in Herzen State Pedagogical University, Saint-Petersburg. For the dating 100 g of dry herbal remains were used. The other two dates, measured by accelerator mass spectrometry, were undertaken by Keck-CCAMS Group, Irvine, California, USA. For the dating beetle remains of Asproparthenis carinicollis (Gyllenhal, 1834) and Otiorhynchus ursus Gebler, 1845 were used. Dates of 12150±90 ¹⁴C BP (UCIAMS-225787) were obtained for Asproparthenis carinicollis (Gyllenhal) and 14200±110 ¹⁴C BP (UCIAMS-225786) for Otiorhynchus ursus Gebler. Obtained radiocarbon dates were calibrated using the Calib Rev 8.1.0. software and curve IntCal20, range ± σ.

Illustrations for the species have been prepared using specimen from the following localities: Apalochrus femoralis pallipes Motschulsky, 1860, neotype, male – Kazakstan, Kokshetau, near Ruzaevka, Ebaeus pedicularius atrotibialis (Tshernyshev 2003), holotype, male, paratype, female – Russia, West Siberia, Gornyi Altai, near Kosh-Agach, E. rufipes Morawitz, 1861 – Russia, West Siberia, Gornyi Altai, near Kosh-Agach, E. ukokus Tshernyshev, 2006 – Russia, West Siberia, Gornyi Altai, Ukok Plateau.

The beetles were studied using an Amscope trinocular stereomicroscope (Ultimate Trinocular Zoom Microscope 6.7X-90X Model ZM-2TY) and digital photographs were taken using a Carl Zeiss Stemi 2000 trinocular microscope and the AxioVision 6.0 program.

Nine fragments of soft-winged flower beetles were extracted from the Quaternary deposit Ustyanka. One fragment, elytron, was found in sample 2 of section II, 2013, depth 5.0-5.2 m, and eight fragments (1 pronotum and 7 elytra) were extracted from samples 16, 19, 20, 22 and 25 of section I, 2020, depth 4.76-5.35 m (Fig. 2).

Two elytra clearly belong to the Asian subspecies A. femoralis pallipes Motschulsky, 1860 of the genus Apalochrus Erichson, 1840. This subspecies differs from the nominative subspecies by its smaller size, pale-yellow antennae and coxae, and green-blue metallic lustre of the upper surface. Elytra from the deposit were parallel and rounded at the apex with a typical complete and distinct suture, with dense slightly coarse punctures, demonstrating typical characters of the genus Apalochrus Erichson, small size and green-blue colouration are characteristic of A. femoralis pallipes Motschulsky which is widely distributed in Asian steppes and steppe meadows and occurs on cereal plants.

One pronotum and six elytra from the deposit belong to the genus Ebaeus Erichson, 1840 from the tribe Ebaeini. The elytra are typical of the females, being slightly ovoid and narrowed at apex, with indistinct suture, apices lacking impression or appendages. In males, elytral apices are impressed and bear two appendages, the inner as a transparent oval plate on vertical pedicle, and the outer as an oval or cup-shape plate that close the inner one from outer side. The suture in the elytra from the deposit is distinctly visible only in the middle due to the elytra being impressed, punctures that are fine and smoothed. The pronotum transverse, with specific emargination near scutellum, finely punctured and monochromously dark, while the elytra are dark with a yellow spot at the apices near the suture. Fragments of the genus Ebaeus Erichson were found in the deposit with the main differential characters as follows: pronotum uniformly dark, transverse, elytra large, almost completely dark with yellow spots at apex, surface of the elytra and the pronotum with blue metallic lustre and finely punctured. 10 species of dark coloured Ebaeus Erichson with female elytra similar to those found in the deposit are known in Inner Asia, namely Ebaeus adyri Tshernyshev, 2007 (Kazakhstan, Tarbagatai), E. basipes Abeille de Perrin, 1891 (Transcaspian, Turkmenistan), E. erythropus Peyron, 1877 (Kazakhstan; Kyrgyzstan; Mongolia; West Siberia), E. fischeri Fleischer, 1909 (Turkestan), E. legalovi Tshernyshev, 2009 (Primorie, Ussuri), E. milkoi Tshernyshev, 2006 (Kyrgyzstan, Alaj Mountain Range), E. pedicularius (Linnaeus, 1758) (from Europe to Central Asia and West Siberia), E. rufipes Morawitz, 1861 (Europe, Kazakhstan, Turkmenistan, S Russia, West Siberia), E. transbaikalicus Pic, 1912 (Mongolia, East Siberia), and E. ukokus Tshernyshev, 2006 (Russia: West Siberia, Gornyi Altai, Ukok Plateau). Of three of the above, E. pedicularius atrotibialis Tshernyshev, 2003, E. rufipes Morawitz, 1861 and E. ukokus Tshernyshev, 2006, the elytra of females are the most similar to those found in the deposit by the colouration, but significantly shorter them.

Nearly all dark-coloured Ebaeus Erichson species are residents of arborescent-shrub landscapes, and occur on willows, elms or poplars in river valleys, or on bushes in steppes and meadows (Tshernyshev 2003, 2006, 2007). This is the first record of fragments of the tribe Ebaeini being recorded from Quaternary deposits. Recent representatives of the tribe are typical residents of open and intrazonal landscapes, the imago preferring arborescent-shrub vegetation on river banks, but occasionally can be found on cliff stones.

The sample was dated by radiocarbon analysis of plant detritus, yielding an age of: 10806±100 ¹⁴C BP (SPb-1346) (sample 3, 2013) and 10150±200 ¹⁴C BP (SPb-1345) (sample 1, 2013), and coincides with the calibrated age 12698-12838 cal yr BP and 11390-12099 cal yr BP, the end of late glacial – beginning of Holocene.

Insect assemblages from samples 1, 2 and 3 are similar and represented by at least 66 Coleoptera species (Gurina et al. 2019a). Steppe species prevail in the assemblages, with a high share of hygrophilous and halobiont species, such as Dyschiriodes luticola (Chaudoir, 1850), Paratachys centriustatus (Reitter, 1894), Bembidion aspericolle (Germar, 1829), B. gassneri Netolitzky, 1922 (Carabidae) and Megamecus argentatus (Gyllenhal, 1840) (Curculionidae), but tundra and forest species are completely absent. Main part of species revealed from the deposit is typical of modern fauna of the region, and several species are known from steppe zone of Eurasia and distributed southerly or westerly of the location of the deposit Ustyanka-1, namely: Scarites terricola Bonelli, 1813, Paratachys centriustatus (Reitter), Lebia punctata Gebler, 1843 (Carabidae), Aclypaea calva (Reitter, 1898) (Silphidae), Tychius albolineatus Motschulsky, 1860 (Curculionidae).

The Ustyanka-1 insect assemblage strongly differs from late Pleistocene deposits of south-east regions of West-Siberian Plain in species composition (Zinovyev et al. 2016; Gurina et al. 2018, 2019b, 2019c). Nevertheless, some species of the assemblage, such as weevils Otiorhynchus ursus Gebler, 1844 and O. altaicus Stierlin, 1861, are typical of the late Pleistocene but not the recent fauna of the region, their presence allow supposed them re-deposited, although this is not typical to insect remains (Kuzmina 2017). For the verification of this hypothesis, fragments of two Curculionidae species from sample 3 were dated via the AMS method. As a result, a date of 12150±90 ¹⁴C BP (UCIAMS-225787) was determined for the fragment of Asproparthenis carinicollis (Gyllenhal, 1834), the species typical of modern fauna of steppe zone of West-Siberian Plain, and a date of 14200±110 ¹⁴C BP (UCIAMS-225786) for Otiorhynchus ursus, a resident of the late Pleistocene landscape in the region. Calibrated data are 13857-14170 cal yr BP and 17099-17370 cal yr BP.

The AMS data gained demonstrated that (1) previous dating results, were probably somewhat younger due to contemporary carbon penetration of the sample, (2) the insect assemblage from Ustyanka-1 coincides with a warm stage of the late glacial period (Bølling or Allerød), and (3) part of fragment assemblage has probably been re-deposited from Sartan layers (MIS-2).

The first insect assemblage of the late glacial warm stage revealed in the region corresponds with the present-day steppe zone fauna of West Siberia in terms of species composition, which allows one to re-construct the former climate that was warmer and/or drier than those today. The deposit site was surrounded with open steppe landscapes, and presence of a large number of halophilous species of beetles is evidence of strong salinization of the site. Both Malachiid species found in the deposit support these reconstructions.

Data on soft-winged flower beetles in Quaternary deposits are fragmentary, mainly due to the irregular study of insects in such deposits of different regions, and the specificity of the group.

To date, insects in Quaternary deposits have been relatively well studied in West and Central Europe and some northern regions (Scandinavian countries, Belorussia, northern and central regions of West Siberia, NE Siberia, North Canada and Alaska (Nazarov 1984; Elias 1994; Zinovyev 2008, 2011; Kuzmina and Matthews 2012). However, malachiid beetles have not been recorded from deposits in the northern part of the West-Siberian Plain and Belorussia, and from North Europe there is known one record of Malachius sp. from the Holocene in Norway (Barrett et al. 2007). Several reasons explain this phenomenon, such as taphonomic factors, especially the soft and thin cuticle which dictates fragment preservation in deposits and the naturally low numbers of malachiid beetles in northern regions (Tshernyshev 2012b). On the contrary, in West Europe they frequently occur in deposits, being known from 50 localities with more than 100 samples which contain malachiid beetle fragments (Ters et al. 1971; Ashworth 1973; Girling 1980; Rose et al. 1980; Osborne 1997; Ponel et al. 1999, 2007; Kenward 2005; Robinson 2006; Bugs... 2020). It is difficult to explain the unexpected fact that all Quaternary records mentioned above relate to the Holocene or the end of Pleistocene, the deglaciation time, i.e. warm stages of the Quaternary period. To date, no malachiid fragment has been recorded from cryochrons of West Palaearctic. The only record of soft winged flower beetles from deposits of East Europe relates to the Singil warm stage (MIS11) (Bidashko and Proskurin 1987). This regularity is conforming by new recordings for south-eastern regions of West Siberia. No malachiid fragments were found in more than 10 Pleistocene deposits studied in recent years (MIS-3 and MIS-2) (Legalov and Dudko 2016; Zinovyev et al. 2016; Gurina et al. 2018, 2019b, 2019c). The only soft-winged flower beetle fragments were found in several samples of the late glacial warm stage Ustyanka-1 deposit. In North America malachiid beetles are only recorded from Holocene layers (Elias 1992; Devender and Hall 1994; Kuzmina and Matthews 2012; Kuzmina et al. 2014). An unexpected exception to the rule is North East Siberia, where a poor species diversity of Malachiids is found in deposits; only Apalochrini, represented by Protapalochrus arcticus (L. Medvedev), has been regularly recorded from both the Holocene and the Pleistocene deposits (Kuzmina and Matthews 2012); this species currently occurs in the region, preferring relic tundra-steppes of North East Siberia, cold and dry landscapes widely located during glacial periods (Tshernyshev 2012a, b; Chernov at al. 2014).

The malachiid beetles registered in Quaternary deposits are typical for recent regional faunas, and it is appropriate result, because differences in species distribution were revealed for cold periods of Pleistocene, while Holocene fauna was similar to that at the present time (Nazarov 1984; Elias 1994; Kuzmina 2017). Thus, the assemblages of Malachiidae beetles in deposits reflect the contemporary fauna of the regions, those for Europe being Malachiini represented by Anthocomus Erichson, 1840, Axinotarsus Motschulsky, 1854, Cerapheles Mulsant and Rey, 1867, Clanoptilus Motschulsky, 1854, Cordylepherus Evers, 1985, Micrinus Mulsant and Rey, 1867 and Malachius Fabricius, 1775, and for East Asia by Apalochrini Protapalochrus arcticus (L. Medvedev). Newly found fragments from the deposit in West Siberia revealed representatives of two tribes, Apalochrini and Ebaeini.

All malachiids registered in Quaternary deposits of Europe, Anthocomus coccineus (Schaller), A. fasciatus (Linnaeus), Axinotarsus ruficollis (Olivier), Cerapheles terminatus (Ménétries), C. lateplagiatus (Fairmaire), Clanoptilus marginellus (Olivier), Cordylepherus viridis (Fabricius), Micrinus dimorphus Abeille de Perrin, Malachius aeneus (Linnaeus) and M. bipustulatus (Linnaeus) belong to the tribe Malachiini and are typical representatives of the European fauna. Two species, Micrinus dimorphus Abeille de Perr. and Cerapheles lateplagiatus (Fairmaire), recorded from France, Italy, Portugal and Spain, could be regarded as endemic for southern Europe, Axinotarsus ruficollis (Olivier) is widespread in the southern Europe and reaches North Africa, four species, Cerapheles terminatus (Ménétries), Anthocomus coccineus (Schaller), A. fasciatus (Linnaeus) and Clanoptilus marginellus (Olivier) are widely distributed in south-western to south-eastern regions of Europe, and three species, Cordylepherus viridis (Fabricius), Malachius aeneus (Linnaeus) and M. bipustulatus (Linnaeus) are widely distributed in the forest-steppe zone of Eurasia from Europe to East Siberia and Mongolia. The presence of these species in Quaternary deposits of Europe define the specificity of the fauna formation of the region due to the number of species and rich diversity of Malachiini, while in the Oriental region they are almost absent.

Different tendencies in the Quaternary fauna are noticeable in deposits of the north-eastern part of Eurasia, with only one Apalochrini representative, Protapalochrus arcticus L. Medvedev (= Troglocollops arcticus (L. Medvedev) (Tshernyshev 2016), being recorded (Kuzmina 2015). Apalochrini are diverse in south-east Asia, Australia and Africa and represented by a number of locally distributed genera, but only one genus, Collops Erichson, 1840, is recoreded from America. Representatives of the tribe are typical for Eurasia and more diverse in Asian regions with endemic genera Protocollops Evers, Simoderus Abeille de Perrin, Troglocollops Wittmer and Pectapalochrus Tshernyshev.