Introduction

The current state of knowledge of Miocene eulipotyphlan faunas, comprised by Erinaceomorpha and Soricomorpha, is rather poor for the whole northern territories of the Central Asia region, also known as "northern Asia" (Vangengeim 1977; Zazhigin and Voyta 2019) or "North Asia" (Wang et al. 2013). Wang et al. (2013) listed the main Neogene vertebrate fossil-producing localities in Asia, showing the unequal proportion with low numbers of Siberian localities in comparison to dozens of more southern sites in Kazakhstan, Mongolia and especially China. Preliminary descriptions of eulipotyphlan findings from Siberian localities are often above the species level (Zykin 2012; Erbajeva and Alexeeva 2013; Daxner-Höck et al. 2013) or deal with separate taxonomic groups such as shrews (Storch and Zazhigin 1996; Storch et al. 1998; Zazhigin and Voyta 2019). Among Siberian Neogene localities, Tagay-1 is the most important multilayered site due to its geographic position in the far north-east of Siberia and due to the composition of previously recognised taxa, which include different genera of Erinaceomorpha and Soricimorpha (Daxner-Höck et al. 2013). The faunal composition is important for the palaeoenvironmental reconstruction and palaeogeographic analyses of Neogene intracontinental and intercontinental faunal displacements and the expression of regional autochthony. The main purpose of the current paper is to describe in detail all eulipotyphlan findings of Tagay-1 and to analyse the palaeoenvironmental context.

Among the Miocene eulipotyphlan faunas most closely situated to Tagay-1 are those from seven Chinese Inner Mongolia localities: Gashunyinadege, Tairum Nor (Qiu and Wang 1999), Tunggur (Qiu 1996), Amuwusu (Qiu and Wang 1999), Shala, Ertemte and Harr Obo (Storch and Qiu 1983; Storch 1995) and the two Chinese Uygur Autonomous Region localities Suosuoquan and Halamagai (Bi 1999; see review by Qiu and Storch 2005). The following genera were reported: Mioechinus Butler, 1948 (or Amphechinus Aymard, 1850) and Metexallerix Qiu and Gu, 1988 (Qiu 1996; Qiu and Wang 1999), Schizogalerix Engesser, 1980 (Qiu and Storch 2005), Scaptochirus Milne-Edwards, 1867, Yanshuella Storch and Qiu, 1983 and Quyania Storch and Qiu, 1983, Asthenoscapter Hutchison 1968, 1974 (Qiu and Wang 1999), Desmanella Engesser, 1972, Proscapanus Gillard, 1899, Mongolosorex Qiu, 1996 (Qiu and Storch 2005); Sorex Linnaeus, 1758, Zelceina Sulimski, 1962, Alloblarinella Storch, 1995, Cokia Storch, 1995, Paenepetenyia Storch, 1995, Paranourosorex Rzebik-Kowalska, 1978 and Paenelimnoecus Baudelot, 1972 (Storch 1995). Recently Zhang et al. (2021) described undetermined remains of Yanshuella from the Late Miocene micromammalian assemblage of Tuchengzi.

Ziegler et al. (2007) described the rich eulipotyphlan faunas from Oligocene-Miocene deposits of the Valley of Lakes in Central Mongolia. According to their results, the Neogene fauna consisted of four erinaceid genera (Zaraalestes Storch and Dashzeveg, 1997, Palaeoscaptor Matthew and Granger, 1924, Amphechinus and Parvericius Koerner, 1940), three soricid genera, (Gobisorex Sulimski, 1970, Sorex, Builstynia Ziegler, Dahlmann and Storch, 2007) and several findings linked to two undetermined groups of the subfamily Crocidosoricinae, besides talpid remains assigned to Talpidae gen. et sp. indet.

Storch and Zazhigin (1996) described anourosoricines from 14 Neogene localities of south-west Siberia (Russia) and North Kazakhstan with descriptions of new taxa of the genus Paranourosorex. Later, Lopatin (2004a) published a detailed revision of Early Miocene mammalian faunas from three localities of the North Aral Region (Kazakhstan) with detailed descriptions of three erinaceid genera (Galerix Pomel, 1848, Exallerix McKenna and Holton, 1967 and Amphechinus); four talpid genera (Desmanella, Pseudoparatalpa Lopatin, 1999, Myxomygale Filhol, 1890 and Hugueneya Hoek Ostende, 1989), three soricid genera (Gobisorex, Atasorex Lopatin, 2004 and Aralosorex Lopatin, 2004) and an additional crocidosoricine genus, Miocrocidosorex Loptin, 2004 from Ayaguz (East Kazakstan; see Lopatin, 2004b). The North Aral Region is with almost 3.500 km distant from the Tagay-1 locality and the faunal list is composed of different taxa then found to the east. Common genera of the North Aral Region and localities in Mongolia and North China are Amphechinus, Desmanella and Gobisorex, only. In addition, according to Ziegler et al. (2007), Exallerix dissappeared from the Valley of Lakes at the end of the Oligocene; however, according to Lopatin (2004a: 230) this genus still existed in western Asia during the Early Miocene. Therefore, the Tagay-1 fauna is of great importance because of substantial differences in eulipotyphlan composition at generic level with respect to Miocene mammalian assemblages from North China and Mongolia on one hand, and European and west Kazakh assemblages on the other. In addition, when assessing shared genera, we will hardly find Miocene 'north-eastern' and western faunas with common species.

Material and methods

The material of Erinaceomorpha and Soricomorpha investigated in this study comprises 36 fossil specimens from six horizons (Layers 5, 6, 7, 9, 10, 11-2), derived from seven samples (Tab. 1) of the Tagay-1 locality. The findings primarily consist of isolated teeth, dentary fragments and few skull fragments. Dental nomenclature follows Rich (1981) for the erinaceids, Hutchison (1968) for the talpids and Reumer (1984) for the soricids. The measurements were mainly taken according to Storch and Qiu (1983), Reumer (1984), and Ziegler (2006). Teeth of the upper jaw are denoted by upper case letters and those of the lower jaw by lower case letters.

Table 1 Eulipotyphlans from the Tagay-1 locality with sample and technical information. * — layer/sample; ** — micro-CT scanning resolution (micrometers); dex. right; sin. left.
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High-resolution images were taken by using X-ray computed micro-tomography. All analysed specimens were scanned on a NeoScan N80 Scanner at the Core Facilities Centre "Taxon" of the Zoological Institute of the Russian Academy of Sciences (https://www.ckp-rf.ru/ckp/3038). All specimens were scanned in three-slice mode. Preliminary processing was performed with DataViewer ver. 1.5.4.0 (SkyScan, Brucker). The main processing of the tooth structure (3D digital reconstruction, surface rendering and measurements) was performed using Avizo 2019.1 (FEI SAS). The resolution (isotropic voxel size) was 9.30 and 9.56 microns (Tab. 1).

Abbreviations

Institutional abbreviations: NHMW, Natural History Museum Vienna (Austria); ZIN, Zoological Institute of the Russian Academy of Sciences (Russia).

Localities: BUK-A, Late Miocene Builstyn Khudag locality of the Valley of Lakes in Mongolia (Ziegler et al. 2007); ODO-A, Early Miocene Olon Ovoony Khurem locality of the Valley of Lakes in Mongolia (Ziegler et al. 2007).

Measurements: AW, anterior width of upper molariform teeth (Reumer 1984); BL, buccal length of upper molariform teeth (Reumer 1984); H(I1), height of incisor crown (shrews; Reumer 1984); L, teeth length (moles; Storch and Qiu 1983); LL, lingual length of upper molariform teeth (Reumer 1984); PW, posterior width of upper molariform teeth (Reumer 1984); TAW, lower molar talonid width (Reumer 1984); TRL, lower molar trigonid length; TRW, lower molar talonid width (Reumer 1984); W, teeth width (moles; Storch and Qiu 1983); Wdwe, distal width of humerus without epicondyles (moles; Ziegler 2006).

Other abbreviations: dp4, deciduous fourth lower premolar; i, I, lower and upper incisors; m, M, lower and upper molars (first-third); p, P, lower and upper premolars.

Systematic palaeontology

Class Mammalia Linnaeus, 1758

Order Eulipotyphla Waddell, Okada, and Hasegawa, 1999

Suboder Erinaceomorpha Gregory, 1910

Family Erinaceidae Fischer, 1817

Subfamily Erinaceinae Fischer, 1817

Genus Parvericius Koerner, 1940

Parvericius cf. P. buk Ziegler, Dahlmann and Storch, 2007

(Fig. 1a–m, Tabs. 1–2)

Fig. 1
figure 1

Teeth and dentary of Parvericius cf. P. buk Ziegler, Dahlmann and Storch, 2007 from the Tagay-1 locality. a1 ZIN 106023/05 (layer 5/59), left hypoconal flange of M1 (a2 explanatory drawing of M1). b ZIN 106023/27 (layer 7/367), right M2. c ZIN 106023/30 (layer 7/367), right M3 (c1. mesial view; c2 occlusal view; c3 explanatory drawing of M3). d ZIN 106023/29 (layer 7/367), right m1 (d1 occlusal view; d2 buccal view; d3 lingual view). e ZIN 106023/44 (layer 11-2/102), right m1 (ibid.). f ZIN 106023/26 (layer 7/367), right m2 (ibid.). g ZIN 106023/03 (layer 5/59), left m2 in occlusal view. h ZIN 106023/24 (layer 7/367), right m2 in occlusal view. i ZIN 106023/25 (layer 7/367), right m2 in occlusal view. j ZIN 106023/28 (layer 7/367), right m2 in occlusal view. k ZIN 106023/33 (layer 9/135), left fragment of dentary with m2 (dentary: k1 occlusal view; k2 lateral view; k3 medial view; m2: k4 buccal view; k5 lingual view; k6 occlusal view). l. ZIN 106023/07 (layer 5/59), right dp4 (l1 occlusal view; l2 buccal view; l3 lingual view). m ZIN 106023/31 (layer 7/367), left dp4 (ibid.). Abbreviations: abr anterobuccal root; al. m3 alveolus of m3; alr anterolingual root; cn carnassial notch; ecid ectocingulid; encd entoconid; fmt mental foramen; fpst parastylar fold; hc hypocone; hcd hypoconid; (m2), second lower molar; mcd metaconid; pc paracone.; pcd paraconid; pocid postcingulid; prc protocone; prcd protoconid; preci precingulum; precid precingulid. Scale bars are 1 mm.

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Table 2 Tooth measurements (mm) of Parvericius cf. P. buk from the Tagay-1 locality, P. buk Ziegler, Dahlmann and Storch, 2007 from the Late Miocene Builstyn Khudag locality of the Valley of Lakes (Mongolia; Ziegler et al. 2007) and P. montanus Koerner, 1940 from the Miocene Deep River beds (USA; Rich 1981). * — mean/range/n; ** — (Biozone D1; MN 3–5)-(Biozone E; MN 9-13), see Ziegler et al. (2007).
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Locality, Stratigraphy: Tagay-1 section (layers 5, 7, 9 and 11-2; sample 2014) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Left m2 (ZIN 106023/03), fragment of a hypoconal flange of left M1 (ZIN 106023/05), fragment of right dp4 (ZIN 106023/07), right m2 (ZIN 106023/24–26, 28), right M2 (ZIN 106023/27), right m1 (ZIN 106023/29, 44), right M3 (ZIN 106023/30), left dp4 (ZIN 106023/31), left dentary fragment with m2 (ZIN 106023/33); n = 13.

Measurements: See table 2.

Description: All isolated teeth belong to the same species based on size in comparison with other species of Parvericius (Tab. 2). Upper teeth are represented by a fragment of the hypoconal flange of the left M1, with the unworn hypocone and distinct crest between hypocone and the metaloph/metaconule, a slightly worn isolated right M2 and an unworn isolated right M3. The posterior outline of the hypoconal flange of M1 slightly differs from M1 of P. buk from the Builstyn Khudag locality of the Valley of Lakes (sample BUK-A/12+14, biozone E, NHMW 2005z0215/0008; see Ziegler et al., 2007: 110). P. buk shows a deep posterior emargination, whereas the flange of the Tagay M1 is slightly narrower and therefore the posterior emargination is shallower than in the nominative species (Fig. 1a). The M2 bears a well-distinct paracone, protocone with a long preprotocrista, metacone, hypocone with a crest towards metaloph/metaconule; the metaconule is well-developed and forms a triangle facet on the worn tooth due to the fusion of metaloph and metaconule, forming a common structure. Mesostyle undeveloped; the parastyle contacts the paracone by a distinct crest, which we here name "parastylar fold". The M2 fits well to M2 of P. buk from Builstyn Khudag (NHMW 2005z0215/0009; ibid.) except for its larger size (Tab. 2) and the narrower hypoconal flange (Fig. 1b). The tooth proportion fits to M2 of the nominative species. The M3 bears well-distinct paracone and protocone; a precingulum is well-developed, it is divided into two portions by a smoothed vertical crest. The anterobuccal corner clearly shows a small parastylar fold (Fig. 1c). The M3 slightly differs from M3 of P. buk from Builstyn Khudag (NHMW 2005z0215/0002; ibid.) in the more inflated molar crown and larger size (Tab. 2).

The fragments of dp4 bear two sharp almost equal-sized cones, proto- and metaconid (slightly lesser), with a notch between them, and the low paraconid with a smoothed paralophid. Both dp4 have well-developed ecto- and entocingulid; the crowns are broken-off at a similar posterior position (Fig. 1: l, m). Differences in crown size (Tab. 2) do not allow assigning left and right dp4 to the same individual, but they undoubtedly belong to the same taxon. Both m1 bear a short trigonid with the well-developed carnassial and trigonid notches and a wide talonid with a clearly outlined talonid basin. The postentocristid and posthypocristid form the posterior border of the basin with a shallow notch; the hypoconulid is undeveloped. The ecto-, pre- and postcingulid are well-developed. The right m1 (ZIN 106023/29) from layer 7 moderately differs from m1 (ZIN 106023/44) from layer 11-2 in the crown proportion, namely the former seems to be more elongated because it has a narrower talonid in relation to total tooth length compared to the latter (Tab. 1). The former m1 is moderately worn vs. unworn latter m1. In addition, the shape of the posterior talonid crests is different (Fig. 1: d cf. e). Based these differences we propose two morphotypes of m1 represented in Tagay-1: 'elongated' and 'stout.' The m2 display a similar variation in crown proportion and talonid border character states; e.g. the left m2 (ZIN 106023/03) from layer 5 can be assigned to the 'elongated' morphotype; the right m2 (ZIN 106023/33) from layer 9 is assigned to the 'stout' morphotype. The left dentary fragment is massive with a large mental foramen. The dentary bears the m2, damaged alveoli of p4 and m1 and an undamaged single alveolus of m3.

Discussion: Late Oligocene and Miocene erinaceines of northern Asia were reported in numerous works and revised by Qiu and Storch (2005), Daxner-Höck et al. (2013) and Qiu et al. (2013). Detailed descriptions are available for Mioechinus (M. gobiensis Qiu, 1996) from the Miocene Tunggur locality, Tunggur Formation, in Inner Mongolia of China (Qiu 1996), for Metexallerix (M. junggarensis) from the Miocene Fuyun locality, Suosuoquan Formation in Xinjiang Uygur Autonomous Region of China (Bi 1999), for Zaraalestes (Biozone D), Palaeoscaptor (Biozone D), Amphechinus (Biozone D) and Parvericius (Biozones D1, E) from localities of the Valley of Lakes area in Mongolia (Ziegler et al. 2007). These taxa were used here for comparisons. Based on m1 and m2 crown proportions and character states of the available teeth we can state a clear match of the Tagay erinaceine with the genus Parvericius. The Tagay hedgehog is larger than other known species of the genus such as Parvericius montanus and Parvericius buk (Tab. 2), therefore we use open nomenclature for the preliminary description of the Tagay form. The presence of two morphotypes of m1 in our material corresponds to the similarly two morphotypes in Ziegler's material from the Valley of Lakes (Ziegler et al. 2007: 110, 'elongated' morphotype from sample ODO-A/1, biozone D1/1, NHMW 2005z0214/0001; 'stout' morphotype from sample Builstyn Khudag, BUK-A/12+14, biozone E, NHMW 2005z0215/0001).

The spatial and stratigraphic ranges of the genus Parvericius covers Early and Middle Miocene localities in North America and late Oligocene to Early-Late Miocene localities in northern Asia, particularly Nareen [Naran] Bulak (late Oligocene; east Gobi, Mongolia) and Builstyn Khudag (Biozones D1/1, D1/2, E; the Valley of Lakes, Mongolia; Ziegler et al. 2007). In addition, a further revision of Qiu's "Mioechinus? gobiensis" from the Tunggur locality (Middle Miocene; Qiu 1996) could clarify the generic position of this taxon and possibly include it in Parvericius.

Suboder Soricomorpha Gregory, 1910

Family Talpidae Fischer, 1817

Subfamily Desmaninae Thomas, 1912

Desmaninae gen. et sp. indet.

(Fig. 2a–f, Tabs. 1, 3)

Fig. 2
figure 2

Teeth of Desmaninae gen. et sp. indet from the Tagay-1 locality. a ZIN 106024/09 (layer 5/59), right maxilla fragment with P4, M1 (maxilla: a1 occlusal view; a2 buccal view; a3 lingual view; P4: a4 occlusal view; a5 buccal view; a6 lingual view). b ZIN 106024/10 (layer 5/59), left m3 (b1 occlusal view; b2 buccal view; b3 lingual view). c ZIN 106024/34 (layer 9/135), right dentary fragment with p4, m1 (c1 occlusal view; c2 lateral view; c3 medial view). d ZIN 106024/36 (layer 9/135), right m2 (d1 occlusal view; d2 buccal view; d3 lingual view). e ZIN 106024/41 (layer 9/135), left M3 (occlusal view). f ZIN 107165/11 (layer 6/1), right upper non-molariform tooth (occlusal view). Abbreviations: mcl metaconule; msst mesostyle; see also Fig. 1. Scale bars are 1 mm.

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Table 3 Tooth measurements (mm) of Archaeodesmana sp. from the Tagay-1 locality and Archaeodesmana aff. A. vinea (Storch, 1978) from two Late Miocene Austrian localities, Kohfidisch (K) and Schernham (S) (Ziegler 2006).
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Locality, Stratigraphy: Tagay-1 section (layers 5, 6 and 9; sample 2014) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Right maxilla fragment with moderately worn P4-M1 (ZIN 106024/09), left moderately worn m3 (ZIN 106024/10), right dentary fragment with heavily worn p4-m1 and the anterior alveolus of m2 (ZIN 106024/34), right heavily worn m2 (ZIN 106024/36), left moderately worn M3 (ZIN 106024/41) and undetermined upper non-molariform unicuspid tooth (ZIN 107165/11). n = 6.

Measurements: See table 3.

Description: Right upper single-rooted tooth with low and wide cone-like crown (Fig. 2f). The tip is weakly bicuspid (two tips very closely fused). A posterocrista runs from the tip to the posterior edge of the crown, separating the buccal and lingual parts. The cingulum is undeveloped. The radicular part of the tooth is broken-off.

All bones similarly massive with huge root alveoles. The bony material is uninformative and does not bear any distinct characters, except a large mental foramen under the protoconid of m1. Position and size of the foramen corresponds to the genus state. The right P4 is a massive tooth, triangled in occlusal outline, with a wide, inflated paracone. The tooth bears a well-developed postcrista and a very small parastyle on the precingulum. The moderately developed lingual flange bears the small protocone and an additional cusp (hypocone?) situated posteriorly. The ectocingulum is developed in the posterior part (Fig. 2a). The right M1 has the shape of a beveled triangle due to strongly protruding metastyle. The protocone is rounded at the base; the metacone is the highest cone. The parastyle is small and fused with the precingulum similarly to the P4 condition. The mesostyle is clearly split by a deep notch. The lingual portion of the crown is dominated by the large protocone with the well-developed but short pre- and postprotocristae and a small metaconule. The worn state does not allow description of additional features, only that the prepotocrista probably ends in a paraconule (Fig. 2a). The isolated M3 is heavely worn (similar to the M1) with the large paracone, protocone and developed para- and metaconule. The metacone lacks the postmetacrista (Fig. 2e).

The right p4 partly corresponds in the proportions to the P4. The massive inflated crown has a pointed precingulid and a posterolingual cuspule. The cingulid surrounds the crown almost completely (Fig. 2c). The crown of the m1 is heavily worn. Based on the contour of the cuspids we can state the prominent and rounded buccal side of the protoconid. The trigonid is notable narrower than talonid. The cingulids are well developed. The entostylid is of moderate size (Fig. 2c). The crown outline of the isolated m2 is similar to the m1 in shape, with a narrow trigonid and wide talonid. Contrary to the m1, the trigonid is shorter than the talonid; the paraconid is not so inflated on the buccal side. The condition of cingulids and entostylid is similar in both teeth. The left isolated m3 displays a short trigonid and long talonid with similar width of both the parts. The entostylid is absent (Fig. 2b).

Discussion. At present desmanines from late Oligocene and Miocene localities of northern Asia are unknown. Qiu and Storch (2000, 2005) mentioned Desmana sp. from the Pliocene Huade locality (Bilike Local Fauna) in Inner Mongolia of China. Flynn and Wu (1994) listed Desmana nehringi Kormos, 1913 in the Pliocene deposits of the Yushe locality, Gaozhuang Formation, in Shanxi Province of China. These two Pliocene records are the only references for desmanines from North China to Kazakhstan. Qiu et al. (2013) listed Desmana only for the Pliocene Gaozhuangian Chronofauna.

Our material contains isolated teeth and small bone fragments of an undetermined desmanine genus. These remains are similar to Archaeodesmana, but the clear taxonomic determination is restricted by two main aspects: first, the main diagnostic characters of the earliest desmanine genus, Archaeodesmana, are found in the first upper and lower incisors (Rümke 1985; Minwer-Barakat et al. 2008, 2020), but unfortunately these teeth are not represented in the Tagay material; second, the wide temporal gap between the oldest records of Archaeodesmana from European lower Turolian deposits of Dorn-Dürkheim (Storch 1978) and Kohfidisch (Rümke 1985; see also Ziegler 2006) and the older Tagay remains that are assigned to the Early-Middle Miocene (MN5).

Because of the absence of known Asian desmanines for comparison we used data on earliest European species, namely Archaeodesmana aff. A. vinea from the Late Miocene Austrian localities Kohfidisch and Schernham (Ziegler 2006). The Tagay desman is similar in tooth size to Archaeodesmana aff. A. vinea (Tab. 3), and differs from the Austrian form in the proportions of P4 such as slightly longer crown (the posterior part seems longer than in the Austrian form; see Fig. 2a cf. fig. 7:4 in Ziegler 2006) and the moderately developed protocone. The M1 and M3 are similar to the Austrian teeth, however, the worn state does not allow us to clearly compare the degrees of development of the para- and metaconules. In addition, for the Tagay specimens we can clearly observe a mesostyle split on M1 that is absent on M3. In general, the main diagnostic features of the Tagay desmanine are the small parastyle of P4, two distinct cuspules on the buccal flange of P4 (protocone and additional cusp, hypocone?), the split mesostyle and two distinct conules on M1 (see Rzebik-Kowalska 2014: 17). The lower teeth of the Tagay desman clearly fit to the upper teeth based on the size, matching the Austrian tooth dimensions (Tab. 3).

Subfamily Talpinae Fischer, 1817

Genus Quyania Storch and Qiu, 1983

Quyania sp.

(Fig. 3a–b, Tab. 1)

Fig. 3
figure 3

Teeth of Quyania sp. (a, b), humerus fragment of Urotrichini gen. et sp. indet. (c), dentary fragment and teeth of Yanshuella cf. Y. primaeva (d–g) from the Tagay-1 locality. a ZIN 107166/32 (layer 7/367), left M2 fragment with para- and metacone. b ZIN 107166/37 (layer 9/135), left M2 fragment with protocone. c ZIN 106025/15 (layer 7/11), right distal fragment of humerus (c1 anterior view; c2 posterior view). d ZIN 106029/21 (layer 7/367), left talonid of m1 or m2. e ZIN 106029/22 (layer 7/367), left m1 (e1 occlusal view; e2 buccal view; e3 lingual view). f ZIN 106029/39 (Layer 7/367), left M2 fragment with paracone and protocone. g ZIN 106029/20 (layer 7/367), right dentary fragment with m2-m3 and alveoli of m1 (g1 occlusal view; g2 lateral view; g3 medial view). Scale bars are 1 mm.

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Locality, Stratigraphy: Tagay-1 section (layers 7 and 9; sample 2014) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Left M2 fragment with para- and metacone (ZIN 107166/32), left M2 fragment with protocone (ZIN 107166/37).

Measurements: BL (M2) = 1.86 mm (ZIN 107166/32), LL (M2) = 1.20 mm (ZIN 107166/37).

Description: The material is represented by two M2 fragments. The fragment corresponding to the buccal part of the molar (ZIN 107166/32) has well-developed, everted para- and metastyles ('curled' styles by Storch and Qiu 1983: 97). The mesostyle is a fused horseshoe-shaped element (Fig. 3a). The preparacrista is slightly shorter than postmetacrista, therefore the buccal outline seems asymmetrical. Based on size and the mesostyle shape we assign both M2 fragments to the same taxon. The second fragment is unworn and corresponds to the lingual part of the crown (Fig. 3b). The crista rises from the protocone base and passes through paraconule, small protocone and small metaconule and almost reaches the metacone base. The crista (preprotocrista + postprotocrista) is fully isolated in the deep trigon basin.

Discussion: The Tagay molars differ from Quyania chowi Storch and Qiu, 1983 in bigger size: ZIN 107166/32 has a buccal length of 1.86 mm vs. 1.48 mm in Q. chowi. In addition, the Tagay molars have a clearly fused mesostyle vs. the 'incipient twinning of the mesostyle' (Storch and Qiu 1983: 97) of Q. chowi. On the other hand, the detailed comparisons by Storch and Qiu (1983) of Quyania and other talpid genera allow us to assign the Tagay teeth confidently to Quyania instead of Urotrichus Temminck, 1841, Neurotrichus Günther, 1880, Scaptonyx Milne-Edwards, 1872, Geotrypus Pomel, 1848, Desmanella Engesser, 1972 or Yanshuella Storch and Qiu, 1983. The short list of differential characters of Quyania includes: weak protoconule of M2 (vs. strong protoconule in Urotrichus, Scaptonyx, Desmanella and Yanshuella); metacrista (postmetacrista) longer than paracrista (preparacrista) (vs. subequal crests length in Urotrichus); small metaconule (vs. expanded metaconule in Neurotrichus, Geotrypus, Desmanella and Yanshuella); presence of metacingulum of M2 (vs. reduced metacingulum in Scaptonyx); fused preparacrista (vs. gap between style and crest in Paratalpa Lavocat, 1951).

The genus Quyania was described from the Late Miocene Ertemte 2 locality and is known from the Middle Miocene Tunggur locality and Early Pliocene Harr Obo locality in Inner Mongolia of China (Storch and Qiu 1983; Qiu 1996; Qiu and Storch 2005).

Urotrichini gen. et sp. indet.

(Fig. 3c, Tab. 1)

Locality, Stratigraphy: Tagay-1 section (layer 6; sample 2014) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Right distal fragment of humerus (ZIN 106025/15).

Measurements: Distal width without epicondyles (Wdwe of Ziegler 2006) = 4.94 mm.

Description: The right distal humerus fragment has broken-off medial and lateral epicondyles (Fig. 2c). The pit for the M. flexor digitorum profundus is wide and visible in anterior view. The epicondilar foramen is large and opens into the deep supratrochlear fossa. The capitulum is spherical and widely fused with the trochlea with a sharp medial border. The olecranon fossa is deep and clearly delineated.

Discussion: The Tagay humerus is morphologically similar but slightly larger than the humerus fragment of Urotrichini gen. et sp. indet. from the Late Miocene Austrian Schernham 7 locality (Ziegler 2006); Wdwe (Tagay-1) = 4.96 mm vs. Wdwe (Schernham 7) = 4.5 mm. We associated this humerus with an undetermined form of Urotrichini. This bone cannot be associated with the Quyania teeth because they are too small for a tooth-bone size match, i.e. according to Storch and Qiu (1983), the buccal length of M2 of Q. chowi is 50% of Wdwe of humerus (see Storch and Qiu 1983: 97), whereas the buccal length of M2 of the Tagay Quyania sp. is 37% of Wdwe of humerus.

Genus Yanshuella Storch and Qiu, 1983

Yanshuella cf. Y. primaeva (Schlosser, 1924)

(Fig. 3d–g, Tabs. 1, 4)

Table 4 Tooth measurements (mm) of Yanshuella cf. Y. primaeva from the Tagay-1 locality and Y. primaeva (Schlosser, 1924) from Late Miocene-Early Pliocene Chinese Ertemte 1 locality (Storch and Qiu 1983).
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Locality, Stratigraphy: Tagay-1 section (layers 7 and 9; sample 2014) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Right dentary fragment with m2-m3 and alveoli of m1 (ZIN 106029/20), left talonid of m1 or m2 (ZIN 106029/21), left m1 (ZIN 106029/22) and left M2 fragment with paracone and protocone (ZIN 106029/39).

Measurements: see table 4.

Description:The M2 is heavily worn with well-developed everted parastyle. The morphology of the mesostyle is unknown due to damage. Based on the contour of the protocone and its crests we can assume the presence of small para- and metaconule (Fig. 3f).

The left m1 is moderately worn with damaged entoconid area. Talonid and trigonid are subequal in length. The talonid is notably wider than the trigonid. The oblique cristid almost reaches the metaconid, therefore the hypoflexid is very deep. The entostylid is prominent; ectocingulid is well-developed. The pre- and postcingulids are variably developed. The ectocingulid is weak (Fig. 3e). Both m2 and m3 are moderately worn. The trigonid and the talonid are similar in width in the m2, whereas in the m3 the trigonid is wider than the talonid. The general morphology of the m2 and m3 is similar to that of the m1 with one exception, namely the cingulid development. The m2 and m3 have well-developed precingulids, and ectocingulids are more developed than in m1. The oblique cristid of m2 terminates more lingually than in m1. The m3 has no entostylid. The alveoli sizes correspond to roots of the isolated m1. The dentary is uninformative, the mental foramen situated on the absent part of the bone (Fig. 3g).

Discussion: The Tagay material is similar in size to Yanshuella primaeva (Schlosser, 1924) with one exception in the width of m1 (Tab. 4): the Tagay molar is narrower than those of Y. primaeva from its type locality (see Storch and Qiu 1983); another obvious difference is that the molars from the type locality have a more developed ectocingulid, uninterrupted below the protoconid (Lu Li personal communication). The Tagay molars differ from the nominative species in a more expressed hypoflexid. However, the Late Miocene species "?Y. primaeva" from the Chinese Tuchengzi fossil site (Zhang et al. 2021) displays similar conditions of the hypoflexid of m1-m3. A similar pattern with a deep hypoflexid on m1-m3 is expressed, for instance, in Proscapanus (Ziegler 2006: 125, fig. 10), but with a well-developed metastylid. In the Tagay form the metastylid is undeveloped, which is the generic feature of Yanshuella (Storch and Qiu 1983: 115).

The genus Yanshuella was described from the Late Miocene-Early Pliocene Ertemte 1 locality and was also found in the Middle Miocene Tunggur and Amuwusu localities, the Late Miocene Shala locality and in the Early Pliocene Harr Obo, Bilike and Gaotege localities from Inner Mongolia of China, in the Yushe locality in Shanxi Province and also in several localities from more southern regions of China: (Storch and Qiu 1983; Qiu 1996; Qiu and Storch 2005).

Talpidae incertae sedis

Genus Desmanodon Engesser, 1980

Desmanodon sp.

(Fig. 4a–b, Tab. 1)

Fig. 4
figure 4

Teeth of Desmanodon sp. from the Tagay-1 locality. a ZIN 107163/02 (layer 5/59), right m1 (a1 occlusal view; a2 buccal view; a3 lingual view). b ZIN 107163/14 (layer 6/1), right p4 (b1 occlusal view; b2 buccal view; b3 lingual view). Scale bars are 1 mm.

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Locality, Stratigraphy: Tagay-1 section (layers 5 and 6; sample 2014) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Right m1 (ZIN 107163/02) and right p4 (ZIN 107163/14).

Measurements: L (p4) = 1.24 mm; W (p4) = 0.70 mm; L (m1) = 1.74 mm; TRW (m1) = 0.93 mm; TAW (m1) = 1.17 mm.

Description: The m1 is unworn, with a damaged paraconid. Trigonid is shorter than talonid; the talonid is notably wider than trigonid. The protoconid and meta-conid are very close. The oblique cristid extends anteriorly to the protoconid base. The metaconid and entoconid are equal in height. The entocristid closes the talonid basin (Fig. 4a). The entostylid is present. The pre- and ectocingulids are developed.

The p4 is laterally compressed. The main cusp bears the postcristid, which arises at 1/3 height of the cusp (Fig. 4b). The precingulid forms a parastyle-like bulge and passes to the entocingulid; the ectocingulid extends from the midline of the crown backwards.

Discussion. Until now, Desmanodon was unknown in North and Central Asia (Lopatin 2004a; Wang et al. 2013). The genus ranges in Europe from the Oligocene to Late Miocene and consists of eight to nine species (Furió et al. 2014).

The Tagay form is similar in size to Desmanodon crocheti Prieto, 2010 from the Middle Miocene North Alpine foreland basin and partly (by dimensions range) to Desmanodon burkarti van den Hoek Ostende, 1997 (Prieto 2010). The Tagay p4 differs from D. crocheti and D. burkarti in the crown proportions, where the Tagay tooth has a symmetrical triangle shape in lateral view (vs. D. crocheti; see Prieto 2010: 219, fig. 2) and moderately inflated buccal side of the main cusp (vs. D. burkarti; see van den Hoek Ostende 1997: 40, pl. 2). The proportions and crown elements of p4 and m1 from Tagay-1 are similar to Desmanodon larsi Furió, van Dam, Kaya, 2014 from the Upper Miocene deposits of the Sivan Basin of Central Anatolia (Doukas and van den Hoek Ostende 2006; Furió et al. 2014).

Family Plesiosoricidae Winge, 1917

Genus Plesiosorex Pomel, 1848

Plesiosorex sp.

(Fig. 5a–b, Tab. 1)

Fig. 5
figure 5

Teeth of Plesiosorex sp. from the Tagay-1 locality. a ZIN 106027/35 (layer 9/135), right m1 (a1 occlusal view; a2 distal view; a3 buccal view; a4 lingual view; a5 explanatory drawing of talonid part). b ZIN 106027/38 (layer 9/135), right m3 (b1 occlusal view; b2 buccal view; b3 lingual view). Abbreviations: cn carnassial notch; encd entoconid; enn entocristid notch; encrd entocristid; hcd hypoconid; hcld hypoconulid; mcd metaconid; pcd paraconid; pocid postcingulid; prcd protoconid; trdn trigonid notch; white arrow marks anterior direction; see also in Fig. 1. Scale bars are 1 mm.

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Locality, Stratigraphy: Tagay-1 section (layers 9; sample 135) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Right m1 (ZIN 106027/35) and right m3 (ZIN 106027/38) from layer 9 of the Tagay-1 section (n = 2), collected by Erbajeva and colleagues in 2014.

Measurements: L (m1) = 4.28 mm; W (m1, trd) = 2.35; W (m1, tld) = 2.64 mm; L (m3) = 2.05 mm; W (m3) = 1.53 mm.

Description: Large m1, moderately worn with clearly visible crown structures. The main cuspids are high. There are three well-developed notches on the crown: the deep carnassial notch, a notable trigonid notch and the notch of the entocristid (Fig. 5a). The hypolophid gently curves backwards and ends by the well-devel-oped hypoconulid. Cingulids are very weak, except the clear postcingulid (Fig. 5: a2). There are two main roots; the posterior root comprises two fused roots. The anterior root is broken off.

The small m3 is moderately worn (more than m1) with well developed pre- and ectocingulids. The notches are undeveloped, except for the weak entocristid notch.

Discussion: Plesiosoricidae remains are rare in late Oligocene and Miocene deposits of northern Asia and probably often misidentified. The Tagay specimens differ from Plesiosorex fejfari Oshima, Tomida and Orihara, 2017 from the Early Miocene Dota locality, Nakamura Formation (MN 3) of Gifu Prefecture in Japan by their smaller size (Oshima et al. 2017). However, Vladimir Zazhigin (personal communication) determined numerous findings of plesiosoricids from the Sharga 2 locality, Oshin Formation (MN 7-8) of Govi-Altai Aimag in Mongolia (for locality description, see Zazhigin and Voyta 2018), but the Mongolian material is still undescribed. Another species, Plesiosorex aydarlensis Kordikova, 2000 has been described from the Chul'adyr Formation (middle part, ca. MN 4-5) in the Aktau Mountains locality Dzhungarian Alatau, South-Eastern Kazakstan (Kordikova 2000).

We associate the Tagay teeth to the same species based on m1/m3 length ratio. We compared the m1/m3 length ratio for the large species Plesiosorex evolutus Ziegler, 2006 from the early Late Miocene (MN 10) Götzendorf locality in Austria (Ziegler 2006). The length of m3 of P. evolutus is 44.5% of the m1 length. In the Tagay material the length of m3 (ZIN 106027/38) is 47.8% of the m1 length (ZIN 106027/35). The ratio allows us associate both molars.

The Tagay m1 is smaller than m1 of P. fejfari (L (m1) = 5.45 mm; see Oshima et al. 2017: 293); m3 slightly smaller that of P. aydarlensis (L (m3) = 2.16 mm: see Kordikova 2000: 72), however, the Tagay m3 differs from the m3 of P. aydarlensis in the crown proportions (the latter tooth is wider and more inflated). The Tagay molars fit well in size with the European species Plesiosorex germanicus (Seemann, 1938) from the Early/Middle Miocene transition, MN5, however, the talonid of the Tagay m1 is wider (Ziegler and Mörs 2000).

Family Soricidae Fischer, 1817

Subfamily Heterosoricinae Viret and Zapfe, 1951

Genus Heterosorex Gaillard, 1945

Heterosorex sp.

(Fig. 6a, Tab. 1)

Fig. 6
figure 6

Teeth of Heterosorex sp. (a) and Miosorex sp. (b–f) from the Tagay-1 locality. a ZIN 106028/42 (layer 10/292), crown of the right I1 (a1 occlusal view; a2 buccal view; a3 lingual view). b ZIN 106026/12 (layer 6/1), right m1 (b1 occlusal view; b2 buccal view; b3 lingual view). c ZIN 106026/16 (layer 6/1), left M1 with small part of maxilla in occlusal view. d ZIN 106026/17 (layer 6/1), left M2 with small part of maxilla in occlusal view. e ZIN 106026/18 (layer 7/11), left M1 in occlusal view. f ZIN 106026/19 (layer 7/367), left M3 in occlusal view. Scale bars are 1 mm.

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Locality, Stratigraphy: Tagay-1 section (layer 10; sample 2014) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Crown of a right I1 (ZIN 106028/42).

Measurements: H (I1) = 2.67 mm.

Description: The I1 is represented by a damaged crown part. The incisor is large and clearly fissident. The talon is very small. The ectocingulum is very pronounced at the lower part of the crown to 2/3 of the hight. The buccal surface of the crown is covered by wrinkled enamel (Fig. 6a).

Discussion: The Heterosoricinae subfamily is represented in northern Asian late Oligocene and Miocene faunas by Gobisorex Sulimski, 1970, known from several late Oligocene to Early Miocene localities from the Valley of Lakes of Mongolia (Ziegler et al. 2007), by Mongolosorex Qiu, 1996 from the Middle Miocene Chinese Tunggur locality (Qiu 1996) and by undetermined Heterosoricinae from the Middle Miocene Chinese Amuwusu locality (Qiu and Wang 1999). Other genera have been found in more southern regions of China and the North Aral Region of Kazakhstan. Lusorex Storch and Qiu, 2004 has been found in the Early-Middle Miocene Chinese Shanwang locality (Storch and Qiu 2004), Heterosorex was found in the Late Miocene Chinese Shihuiba and Leilao localities (Storch and Qiu 1991), and Gobisorex and Atasorex Lopatin, 2004 are known from the North Aral Region (Lopatin 2004a).

The Tagay incisor is assigned to Heterosorex on the basis of the talon size, overall size and general proportion of the apex, which are similar to those of Heterosorex wangi Storch and Qiu, 1991 from the Shihuiba and Leilao localities.

Subfamily Crocidosoricinae Reumer, 1987

Genus Miosorex Kretzoi, 1959

Miosorex sp.

(Fig. 6b–f, Tabs. 1, 5)

Table 5 Tooth measurements (mm) of Miosorex sp. from the Tagay-1 locality and Crocidosoricinae from the Unkheltseg locality (Ziegler et al. 2007: 134–136).
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Locality, Stratigraphy: Tagay-1 section (layers 6 and 7; sample 2014) from Olkhon Island, Baikal Region, Siberia; Tagay Formation; Lower/Middle Miocene transition, MN5.

Material: Right m1 (ZIN 106026/12), left M1 with small part of maxilla (ZIN 106026/16), left M2 with small part of maxilla (ZIN 106026/17), left M1 (ZIN 106026/18) and left M3 (ZIN 106026/19).

Measurements: See table 5.

Description: One of the M1s (ZIN 106026/16) and M2 are heavily worn. The other M1 is unworn and displays characteristic features of the crown with an oblique buccal outline contour, slightly expressed parastyle and single prominent mesostyle. The postmetacrista is longer than preparacrista. The protocone is massive; the end of the postprotocrista is turned toward the metacone base. The hypocone is very weakly expressed as a bulge on the hypoconal flange ridge. The precingulum is weak and short (Fig. 6e). The M2 is similar to M1 in the main features, except for the general shape of the tooth, where the buccal outline is more straight due to subequal size of the prepara- and postmetacrista (Fig. 6d). The M3 is moderately worn. The crown bears a large paracone and a small protocone. The crests are represented by the preparacrista, which is the longest, a shorter premetacrista and the postparacrista, which is the shortest (Fig. 6f).

The m1 is unworn. The trigonid and the talonid are equal in length. The trigonid width is narrower than the talonid. The pre- and postcingulids are well-developed; the ecto- and entocingulids are weak (Fig. 6b). The enamel pigment is not visible due to diagenetic changes.

Discussion: Ziegler et al. (2007: 134–136) described three Crocidosoricinae gen. et sp. indet. from the Early Miocene Unkheltseg locality (Biozone D). The Tagay m1 differs from these teeth by a weak ectocingulid and different crown proportion (ratio between trigonid/talonid width together with the tooth length; see Tab. 5). Zazhigin and Voyta (2018) described a crocidurine shrew, Shargainosorex Zazhigin and Voyta, 2018 from the Middle Miocene Mongolian Sharga 2 locality. This shrew is slightly larger than the Tagay form (Tab. 6). Other differences are the well-developed cingulids in the lower teeth of Shargainosorex and a slightly longer trigonid length than talonid length in m1. The M1 of the Tagay form differs from Shargainosorex and the European Miosorex Kretzoi, 1959 in the presence of the bent postprotocrista end. In addition, M. grivensis (Depéret, 1892) and M. pusilliformis (Doben-Florin, 1964) are larger than the Tagay form. M. desnoyersianus (Lartet, 1851) from the Sansan locality is similar in size (see Doben-Florin 1964; Ziegler 1989; Engesser 2009; Zazhigin and Voyta 2018).

Table 6 Tooth measurements (mm) of Miosorex sp. from the Tagay-1 locality, Miosorex grivensis (Depéret, 1892) from the Middle Miocene (MN 7/8) La Grive St. Alban locality in France and Shargainosorex angustirostris Zazhigin and Voyta, 2018 from the Middle Miocene Mongolian Sharga 2 locality (Zazhigin and Voyta 2018).
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Conclusions

The current paper is a preliminary attempt to describe the eulipotyphlan fauna from the Early/Middle Miocene (MN5) of the Tagay-1 locality. Our results reveal a relatively rich faunal composition including European, Asian and North American genera. The North American element in our material is Parvericius (Parvericius cf. P. buk in Tagay), which was first found in northern Asia by Ziegler et al. (2007) in localities of the Valley of Lakes. European faunal elements are represented by Desmaninae gen. et sp. indet. that is very similar to European Archaeodesmana. These findings are the first report of desmans for northern Asia. In addition, Plesiosorex shrews have been described mostly from Europe (Ziegler and Mörs 2000), while in Asia only three findings have ben reported from Japan, Thailand and south-eastern Kazakstan (Kordikova 2000; Peigné et al. 2009; Oshima et al. 2017). The Tagay form can only be attributed to Plesiosorex sp. The other two soricids are the European Heterosorex (in Tagay Heterosorex sp.) and Miosorex (in Tagay Miosorex sp.). In Asia, we know at present only one Late Miocene species of Heterosorex (H. wangi), whereas in Europe at least four species are known from Miocene localities (Ziegler and Mörs 2000; Ziegler 2009). The Miosorex group is represented in northern Asia only by the Mongolian Miocene Shargainosorex, other species of Miosorex s. str. are known from European Miocene localities (Ziegler and Mörs 2000). Desmanodon was also found in European Miocene deposits (Prieto 2010). In the Tagay fauna the Desmanodon sp. finds are the first record for northern Asia, and probably for the whole of Asia. Clearly Asian elements in the Tagay-1 fauna are the moles Quyania sp. and Yanshuella cf. Y. primaeva. Thus, we can describe nine eulipotyphlan taxa including erinaceomorphs and soricomorphs. We used an open nomenclature due to very fragmented and scarce dental material.

An important purpose is the reconstruction of palaeo-enviromental conditions of the local fauna habitats. Previous attempts have been made by Daxner-Höck et al. (2013), who supposed a riverine woodland environment. Our small mammal assemblage of the Tagay-1 section allow us to support the earlier reconstruction of the local palaeoenviroment with forms linked to habitats such as closed forest and open ecotonal habitats, preferred by the ground-dwelling hedgehogs Parvericius, shrew moles Quyania and shrews Plesiosorex, Heterosorex and Miosorex; and subterranean forms such as the digging mole Yanshuella. The presence of desmans allows us to suppose running waters and probably wetland areas that could have also been inhabited by shrews.