Late Oligocene leaf and pollen flora of Southwestern Siberia: taxonomy, biogeography and palaeoenvironments View supplementary material

Thomas Denk

Late Oligocene leaf assemblages from four sites in Southwestern Siberia (Kurgan, Tyumen, Omsk oblasts) are described. Twenty-three leaf taxa and 3 reproductive structures represent local vegetation of a lake (Salvinia, Typha, Phragmites, Nelumbo, Hemitrapa, Liquidambar, Pterocarya, Alnus, Populus, Salix, Nyssa). Additionally, 57 spore and pollen taxa were recorded from one site (Shish River). Gymnosperms dominate the assemblage with ~30% Pinaceae and ~25% taxodiaceous (papillate) Cupressaceae pollen. Ferns and peat mosses (Sphagnaceae) comprised ~6%. Angiosperms were dominated by Fagaceae, Betulaceae, Juglandaceae and Ulmus and comprised a few exotic elements (Liquidambar, Eucommia, Nyssa, Symplocos); scarce herbaceous plants reflect lakeshore vegetation. The flora of the Turgay type comprised old elements (Nelumbo protospeciosa, Liquidambar europaea, taxodiaceous/papillate Cupressaceae, Quercus sect. Protobalanus) and taxa present in Siberia/Kazakhstan during the Paleogene with later arrivals in Europe (Ulmus pyramidalis, Quercus pseudocastanea, Alnus julianiformis, Byttneriophyllum tiliifolium). A few taxa were endemic in the late Oligocene of western Siberia (Trapa praeconocarpa, Platycrater iljinskajae sp. nov.). Combined macrofossil and palynological evidence places the Shish River site flora into the late Oligocene Zhuravka (Turtas) Formation. Floras of similar composition from western Eurasia are commonly middle Miocene or younger in age highlighting the dynamic spatiotemporal evolution of temperate Eurasian floras during the Cenozoic.

Historical Biology An International Journal of Paleobiology ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/ghbi20 Late Oligocene leaf and pollen flora of Southwestern Siberia: taxonomy, biogeography and palaeoenvironments Thomas Denk , Johannes Martin Bouchal , Pavel Smirnov & Yaroslav Trubin To cite this article: Thomas Denk , Johannes Martin Bouchal , Pavel Smirnov & Yaroslav Trubin (2020): Late Oligocene leaf and pollen flora of Southwestern Siberia: taxonomy, biogeography and palaeoenvironments, Historical Biology To link to this article: https://doi.org/10.1080/08912963.2020.1839064 View supplementary material Published online: 11 Dec 2020. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=ghbi20 HISTORICAL BIOLOGY https://doi.org/10.1080/08912963.2020.1839064 Late Oligocene leaf and pollen flora of Southwestern Siberia: taxonomy, biogeography and palaeoenvironments Thomas Denk a , Johannes Martin Bouchal b , Pavel Smirnov c and Yaroslav Trubinc a Swedish Museum of Natural History, Department of Palaeobiology, Stockholm, Sweden; bDepartment of Oto-Rhino-Laryngology, Research Group Aerobiology and Pollen Information, Medical University Vienna, Vienna, Austria; cLaboratory of Sedimentology and Paleobiosphere Evolution, University of Tyumen, Tyumen, Russia ABSTRACT ARTICLE HISTORY Late Oligocene leaf assemblages from four sites in Southwestern Siberia (Kurgan, Tyumen, Omsk oblasts) are described. Twenty-three leaf taxa and 3 reproductive structures represent local vegetation of a lake (Salvinia, Typha, Phragmites, Nelumbo, Hemitrapa, Liquidambar, Pterocarya, Alnus, Populus, Salix, Nyssa). Additionally, 57 spore and pollen taxa were recorded from one site (Shish River). Gymnosperms dominate the assemblage with ~30% Pinaceae and ~25% taxodiaceous (papillate) Cupressaceae pollen. Ferns and peat mosses (Sphagnaceae) comprised ~6%. Angiosperms were dominated by Fagaceae, Betulaceae, Juglandaceae and Ulmus and comprised a few exotic elements (Liquidambar, Eucommia, Nyssa, Symplocos); scarce herbaceous plants reflect lakeshore vegetation. The flora of the Turgay type comprised old elements (Nelumbo protospeciosa, Liquidambar europaea, taxodiaceous/papillate Cupressaceae, Quercus sect. Protobalanus) and taxa present in Siberia/Kazakhstan during the Paleogene with later arrivals in Europe (Ulmus pyramidalis, Quercus pseudocastanea, Alnus julianiformis, Byttneriophyllum tiliifolium). A few taxa were endemic in the late Oligocene of western Siberia (Trapa praeconocarpa, Platycrater iljinskajae sp. nov.). Combined macrofossil and palynological evidence places the Shish River site flora into the late Oligocene Zhuravka (Turtas) Formation. Floras of similar composition from western Eurasia are commonly middle Miocene or younger in age highlighting the dynamic spatiotemporal evolution of temperate Eurasian floras during the Cenozoic. Received 1 September 2020 Accepted 15 October 2020 Introduction Modern plant biogeographic patterns including the disjunct distribution of the north temperate woody flora in eastern and western North America, western Eurasia, and East Asia were established during the Cenozoic (Latham and Ricklefs 1993; Manchester 1999). Migrations of temperate plants from East Asia to western Eurasia included vast areas of northern Russia and Central Asia, which today are characterised by arid steppe and cold boreal climates (Kottek et al. 2006). In Western Siberia, tectonic uplift at the end of the Eocene led to a marine regression and by the early Oligocene a continental regime of sedimentation was established (Arkhipov et al. 2005). From the Oligocene onwards, modern temperate tree taxa constituted an important part of the palaeovegetation, many of which had originated in East Asia and arrived in western Eurasia in the Oligocene (Zhilin 1989, 2001; Walther 1994; Mai 1995). Because of the dynamic spatiotemporal evolution of this temperate flora, it is difficult to correlate Eastern Siberian, Western Siberian, and western Eurasian floras, and inferring ages of fossil floras based on strict biostratigraphical grounds may be misleading. For example, members of Quercus sect. Cerris occurred in Northeast Asia during the early Oligocene, but arrived in western Eurasia no earlier than the Oligocene/Miocene boundary (Denk et al. 2017). Fagus and the extinct genus Chaneya were present in East Asia and western North America during the Eocene and arrived in Central Asia (Kazakhstan) and Europe in the Oligocene (Wang and Manchester 2000; Teodoridis and Kvaček 2005; Denk and Grimm 2009a; Feng and Jin 2012; Hofmann et al. 2019). At the species level, Alnus julianiformis (as A. feroniae) occurred in the Aquitanian (early Miocene) floras of western Kazakhstan (Zhilin 1989) and arrived in KEYWORDS Biostratigraphy; palaeobotany; palaeopalynology; biogeography; Cenozoic; Eurasia; Quercus section Protobalanus Europe during the Burdigalian (Kvaček and Holý 1974). Alnus schmalhausenii was a characteristic element of early Oligocene floras in western Kazakhstan (Zhilin 1989) and very similar forms occurred in the late Oligocene and early Miocene of the western and eastern Mediterranean region (Saporta 1891; Velitzelos et al. 2014). Stratigraphic schemes for the Paleogene and Neogene of Western Siberia have been proposed using carpological data (e.g. Nikitin 2006) and, primarily, palynological data (e.g. Arkhipov et al. 2005; Kuzmina and Volkova 2008; Gnibidenko et al. 2011; Volkova et al. 2016; Kuzmina et al. 2019). A stratigraphic scheme for western Kazakh leaf floras was suggested by Zhilin (1974, 1989)). For some of these pollen and leaf floras their correlation with vertebrate faunas and marine molluscs provided independent age constraints. Key sections for dating fossil plant assemblages of southwestern Siberia and Western Kazakhstan included the Baygubek Formation (Horizon) of the North Ustyurt region and the Aral Formation in the North Aral region (e.g. Zhilin 1989). Marine molluscs of the lower and upper Baygubek Formation and vertebrate remains in the Aral Formation (Akespe locality) provided evidence for the Aquitanian age of the upper Baygubek Horizon and the Aral Formation and their leaf and spore-pollen assemblages (Zhilin 1989). Based on this correlation, the age of major pollen and spore zones (pollen assemblages) in adjacent southwestern Siberia was established (e.g. Unified regional stratigraphic schemes for Neogene and Paleogene deposits of the West Siberian Plain 2001). More recent stratigraphic correlations of marine sediments across Eurasia placed the Baygubek Formation in the late Oligocene (Chattian; Popov et al. 1993, 2004). Likewise, in the North Aral region, ‘Aquitanian’ layers with Paraceratherium CONTACT Thomas Denk thomas.denk@nrm.se Swedish Museum of Natural History, Department of Palaeobiology, Stockholm 10405, Sweden Supplemental data for this article can be accessed here. © 2020 Informa UK Limited, trading as Taylor & Francis Group Published online 11 Dec 2020 2 T. DENK ET AL. according to Zhilin (1989, p. 230) and micromammals of a key sequence exposed at Akespe (Lucas et al. 1998; Lopatin 2004; Bendukidze et al. 2009) indicate a Chattian age for the Aral Formation. Independently, correlation of dinocyst assemblages across Eurasia in combination with regional palynological and palaeomagnetic data has recently resulted in a revised stratigraphic framework for the West Siberian Plain (Gnibidenko 2007; Gnibidenko et al. 2011, 2014; Volkova et al. 2016). This stratigraphic framework is in agreement with the revised stratigraphy proposed for the North Ustyurt and North Aral regions and is here followed. In the present paper, we describe four small plant assemblages from Southwestern Siberia (Kurgan, Tyumen, and Omsk oblasts) and establish biogeographic relationships of the fossil-taxa with Cenozoic plant assemblages and with modern taxa. For one of the studied sites, we also investigated dispersed spores and pollen. We discuss the age of the plant-bearing sites based on comparisons with palynological and macro-palaeobotanical data from the region. Finally, we infer palaeoenvironments based on the ecological properties of the constituting plant taxa. Materials and methods The material investigated here was collected in the 1950s by Sergei Sukhov from natural outcrops. In 1992, his son donated the collection to the ‘Regional Tyumen Museum Complex named after Ivan Slovtsov’. Macrofossils deposited in the collections of the Regional Tyumen Museum bear labels indicating the taxon name and the specimen number with the additional prefixes ДВХ and ОФ. The latter mean Основной фонд (main collection) and Дополнительный внутренний фонд хранения (additional internal storage collection). In addition, specific information about the storage location is indicated on the specimens (e.g. I-1-2; see Appendix 1 for complete label information of the investigated specimens along with previous and current determination). The four sites studied in the present paper were exposed along small tributaries of the Irtysh River (Shish River site, Bicha River site, and Turtas River site) and of the Tobol River (Kizak River site; Figure 1) and are located between 56 and 59°N in the West Siberian Plain. General geology Oligocene strata in Southwestern Siberia are represented mainly by continental deposits comprising silt, clay, sandy clay, and sand. Four stratigraphic horizons are distinguished (Figure 2). These are the Isi’kul’ Formation (corresponding to the Atlym Formation on the right bank of the Irtysh), Novomikhailovka Formation, Zhuravka Formation (replaced by the coeval Turtas Formation in the central and northern regions of the West Siberian Plain), and the Abrosimovka Formation (Volkova et al. 2016, Figure 2, 3). The lower Oligocene Isi’kul’ (Atlym) Formation reflects mainly lacustrine alluvial sedimentation and is composed of sands with clays and silts (Kuz’mina and Volkova 2008). During deposition of the following Novomikhailovka Formation, sediments accumulated in a single sedimentary basin in the vast area of the West Siberian Plain. The formation is made up of alternating rusty-brown clays, silts, and sand with lignite seams. The intensification of tectonic movements during deposition of the upper Oligocene Zhuravka horizon led to the isolation of the Turtas and Zhuravka basins, which were separated by latitudinally oriented uplands. Figure 1. Map of Southwestern Siberia, Irtysh River with the locations of the Turtas, Kizak, Bicha and Shish River sites. Further sites relevant for the age determination of the Shish leaf and spore/pollen assemblage are indicated (a–g). a. Zashchitino Village (Volkova et al. 2016), b. Borehole 8, Om Basin, Southwestern Siberia (Gnibidenko et al. 2011), c. Zyryanskaya-1 borehole, southwestern Tyumen region (Oreshkina et al. 2020), d–f. Bigila, Pyatkovo, and Masali villages (Kuz’mina et al. 2019). g. Neverovka Village, Borehole 1 (Kuz’mina and Volkova 2001). h. Chistoozernyi Village, Borehole 13 (Kuz’mina and Volkova 2008). The Zhuravka horizon includes the Zhuravka and Turtas formations, of which the latter comprises greenish-grey clays and siltstones enriched with thinly layered glauconite, with interlayers of diatomites. The position of the Turtas Formation in the regional stratigraphic scheme of the Paleogene deposits of Western Siberia has been intensively studied. Currently, the late Oligocene (Chattian) age of the formation is corroborated by marine molluscs and micromammal data from the North Ustyurt and North Aral regions and by palynological data (Volkova et al. 2000, 2016) and correlation with dinocysts and palaeomagnetic data (Volkova et al. 2016; Oreshkina et al. 2020). According to Shatsky (1978) the Turtas Formation is a deeper water facies of the central part of the basin, while the coeval Zhuravka Formation is a marginal facies developed in the Kulunda and Baraba steppes, Omsk and Pavlodar Irtysh regions (Zaltsman 1968; Zykin 2012). Hence, the main distribution of the Zhuravka Formation facies is slightly to the southeast of the outcrops investigated for the present study (Figure 1). The four sites investigated here, lie within the boundaries of the Turtas Formation (Oreshkina et al. 2020). Further differentiation of lake basins continued during the later Oligocene and Miocene as the Abrosimovka and later formations were deposited. The Abrosimovka Formation is composed of clays and silts with interlayers of sand and lignite. The age of the Abrosimovka horizon has initially been established by comparing its spore-pollen spectra with those of the upper Baygubekian subhorizon of the Aral Sea and North Ustyurt regions (Boytsova and Panova 1973). The stratigraphic position of the Abrosimovka Formation (horizon) has been a matter of debate and has variously been ascribed to the late Oligocene (e.g. Dorofeev 1963; Zykin 2012) and to the early Miocene (e.g. Zhilin 1989; Unified regional stratigraphic schemes for Neogene and Paleogene deposits of the West Siberian Plain 2001) based on stratigraphic correlation with the upper subhorizon of the Baygubekian Formation (Suite) of the North Ustyurt region. Considering the revised stratigraphy of the North Ustyurt and the North Aral regions (Popov et al. 2004; HISTORICAL BIOLOGY 3 Figure 2. Geological section of the Paleogene-Neogene sedimentary rocks in Southwestern Siberia (based on borehole 8, ’b’ in Fig. 1; Gnibidenko et al. 2011) and its correlation with magnetostratigraphic section. Drawing the Paleogene/Neogene boundary above the Ambrosimovka Formation follows Volkova et al. (2016) and is further discussed in the text. The leaf and pollen-spore assemblages of the Shish locality are correlated with the late Oligocene Zhuravka Horizon and the Turtas Formation. Bendukidze et al. 2009; Zhang et al. 2018) a late Oligocene age seems more plausible. Further, in view of the uniformity of spore-pollen and dinocyst assemblages between the Turtas and Abrosimovka formations, Volkova et al. (2016) established the Abrosimovka Formation as the last stage in the development of the vast lacustrine basin (Turtas SeaLake) in the West Siberian Plain in the late Oligocene (Figure 3). Between the Abrosimovka Formation and the Beshcheul Formation, a locally distinct horizon is recognised by some authors (e.g. Zykin 2012) as lowermost Miocene Ombinsk horizon composed of lake, river, and lake-peat deposits (corresponding to sporepollen assemblage SPA4 in Volkova et al. 2016). The lower Miocene Beshcheul Formation is composed of brownish-grey sands with clay interlayers. The occurrence of this formation is confined to a rather extensive river network with a northward flow. The sedimentation environment of the Tavolzhan (Kalkaman) horizon is characteristic of a low-lying, accumulative plain with a large number of shallow lakes. Its age is determined chiefly by the fauna of mammals corresponding to zones MN 9 and 10 of the Neogene of Eurasia. A feature relevant for the present study is the Turtas Sea-Lake, comparable in scale to the Paleogene marine basins that existed during the late Oligocene in most of Western Siberia and comprised several large inland water bodies (Smirnov et al. 2017; Oreshkina et al. 2020). It was the development of this large intracontinental freshwater hydro-system, its gradual disintegration into a system of individual water bodies, degradation, waterlogging, with the subsequent development of lake-alluvial sedimentation conditions that determined the evolution of the region during the late Oligocene. Processing of the palynological sample The palynological sample was obtained from a slab collected by Sukhov from the Shish River locality. It is part of the Sergei Sukhov collection, stored at the ‘Regional Tyumen Museum Complex named after Ivan Slovtsov’. The rock sample was processed using standard methods (40% HF to dissolve silica, 20% HCl to dissolve fluorspar, chlorination, acetolysis; Halbritter et al. 2018). The residue was transferred to glycerol and is stored at the Swedish 4 T. DENK ET AL. Figure 3. Updated stratigraphic scheme for Southwestern Siberia (modified from Volkova et al. 2016). Floristic levels after Nikitin (2006); regional palynozones after Unified regional stratigraphic schemes for Neogene and Paleogene deposits of the West Siberian Plain (2001); spore-pollen assemblages after Kuzmina and Volkova (2008) and Volkova et al. (2016).The Zhuravka and Abrosimovka horizons (formations) of Southwestern Siberia are correlated with strata containing marine molluscs from the North Ustyurt region (Popov et al. 2004) and with continental deposits of the North Aral region with a rich micromammal fauna (Bendukidze et al. 2009), both being of Chattian age. Further, homogenous dinocyst assemblages of the Zhuravka and Abrosimovka horizons and their correlation with Chinese dinocyst assemblages, corroborate a Chattian age of these horizons. Museum of Natural History in Stockholm under collection numbers S184995–184999. Five hundred palynomorphs were counted and identified (Table 3; Appendix 2) in LM investigation for palynomorph abundance determination. Scanning electron microscopy (SEM) investigation of the palynomorphs is still ongoing. For the present study, biogeographically important members of Fagaceae were documented with SEM to assign them to infrageneric groups of the genus Quercus. The protocol of SEM investigation follows Bouchal et al. (2020). containing leaf imprints was processed for palynological investigation. The spores and pollen identified from this sample are listed in Table 2 and their abundances in Table 3 (see also Appendix 2). Class Polypodiopsida Cronquist, Takht. & Zimmerm. 1966 Family Salviniaceae Martinov 1820 Genus Salvinia Ség. 1754 Salvinia sp.(Figure 4(a)) Material examined – Kizak 3043 I-1-2 Systematic Palaeobotany In the following, 1 fern and 25 angiosperm taxa are described (Table 1). Angiosperm taxa are arranged following The Angiosperm Phylogeny Group (2016). For the Shish River site, a small piece from a slab Description Two floating leaves, ca. 1 cm across, lamina almost round, venation obscure, a striate or punctate pattern on the lamina may reflect secondary veins and/or hairs/papillae. HISTORICAL BIOLOGY 5 Table 1. Leaf and fruit fossil-taxa from four localities in Southwestern Siberia and their preferred habitats. Taxon Polypodiopsida Salvinia sp. Coniferales Coniferales, fam., gen. et spec. indet Angiosperms Poaceae Typha latissima Phragmites oeningensis Nelumbonaceae Nelumbo protospeciosa Altingiaceae Liquidambar europaea Ulmaceae Ulmus pyramidalis Fagaceae Quercus pseudocastanea Quercus kubinyii Juglandaceae Pterocarya paradisiaca Juglans zaisanica Betulaceae Alnus julianiformis Alnus vel Corylus Betula sp. Carpinus grandis Salicaceae Populus balsamoides Populus glandulifera Populus latior Populus sp. Salix lavateri Lythraceae Hemitrapa praeconocarpa Tiliaceae Byttneriophyllum tiliifolium Nyssaceae Nyssa sibirica Hydrangeaceae Hydrangea (Platycrater) iljinskajae Incertae sedis Fam., gen, et spec., indet 1 Fam., gen, et spec., indet 2 Ecology Shish River Kizak River AQ + ? + AQ AQ + + AQ + R + R Z Z Turtas River + ++ ++ + R R + R R Z Z + + R R R R R + AQ Bicha River + + + + + + + +++ + + + ++ + R + R + Z + ? ? + + + + +++ = ≫ 10 specimens; ++ = 5–10 specimens; + = 1–4 specimens AQ = aquatic habitat, R = riparian and swamp forest habitat, Z = zonal, well-drained forest habitat Note that riparian elements may also have formed part of the zonal vegetation Remarks Salvinia had a wide distribution across Eurasia from Eocene to Miocene. From Western Siberia, Dorofeev (1963) described several species of Salvinia based on reproductive structures. Our leaves are very poorly preserved but are clearly roundish in outline and relatively small. Knobloch and Kvaček (1976) suggested using the name Salvinia mildeana Göpp. for poorly preserved leaf remains. Salvinia mildeana from the type locality Sosnica (Schossnitz, late Miocene) has oval leaves unlike the ones reported here. Based on lamina shape, size, and venation, the fossil leaves from Kizak resemble the Miocene Salvinia sunschae Palib. (Shaparenko 1956). Spores of Salvinia were not encountered in the Shish River site pollen sample. Class Coniferopsida Cronquist, Takht. & Zimmerm. 1966 Order Coniferales Gorozh.1904 Coniferales fam. et gen. indet. (Figure 4(b)) Material examined – Kizak 9187–25 Description Leaf fragment, ca. 3 cm long, 0.3 cm wide, oblong, apex bluntly acute, mid-vein strong, flanked by two stomatal bands, margin thickened. Remarks A few leaf remains do not provide sufficient information to ascribe them to a particular family and genus in the Coniferales. In general, the macrofossil record is almost void of conifer leaves and reproductive structures, whereas conifers are the most prominent elements in the pollen record. Clade AngiospermaeOrder Poales Small 1903 Family Typhaceae Juss. 1789Genus Typha L. 1753 Typha latissima A.Braun 1849 (Figure 4(c–e)) Typha latissima A.Braun – Braun in Bruckmann 1849, p. 227 Typha latissima A.Braun – Braun in Stitzenberger 1851, p. 75 Typha latissima A.Braun – Heer 1855, p. 98, pl. 43–44 Typha latissima A.Braun – Kolakovsky 1964, p. 36, pl. 5, figs 4–6 Typha latissima A.Braun – Iljinskaja 1968, p. 45, pl. 14, figs 3, 4 6 T. DENK ET AL. Table 2.: Spore and pollen fossil-taxa from the Shish River site and their preferred habitats. Note that a number of conifers that are today found on well-drained soils, were part of peat forming vegetation during large parts of the Cenozoic (Schneider 1992; Dolezych and Schneider 2006, 2007, 2012). Dispersed spores and pollen from the leaf-bearing layer of the Shish River site Spores Laevigatosporites haardtia Sphagnum Osmundaceae Trilete Spores Lycophyta Gymnosperms Cupressaceae Papillate Cupressaceae Pinaceae Pinus Haploxylon Pinus Diploxylon Picea Cathaya Larix Abies Tsuga (2 types) Angiosperms Potamogetonaceae Potamogeton Poaceae Poaceae? Typhaceae Typha Cyperaceae Carex Nelumbonaceae Nelumbo Altingiaceae Liquidambar Vitaceae Parthenocissus (L) Salicaceae Salix Rosaceae Rosaceae gen indet. Ulmacae Ulmus Fagaceae Castaneoideae Fagus Quercus sect. Cerris Ecology R R AQ R R R AQ R AQ AQ R R AQ R Z Z Z Z Z Z Z Z Z AQ AQ R AQ R AQ R Z AQ R R Z R R Z R Z Z Z Fagaceae Quercus subgen. Quercus sect. Protobalanus Quercus subgen. Quercus excl. sect. Protobalanus Myricaceae Myrica Juglandaceae Carya Pterocarya Juglans Betulaceae Alnus Carpinus Betula Corylus Lythraceae Hemitrapa vel Trapa Lythrum Onagraceae Ludwigia Nitrariaceae Nitraria Sapindaceae Acer (2 types) Malvaceae Tilia Santalaceae Arceuthobium (P) Amaranthaceae Amaranthaceae gen. indet. Nyssaceae Nyssa Ericaceae Ericaceae (3 types) Symplocaceae Symplocos Eucommiaceae Eucommia Oleaceae Fraxinus Aquifoliaceae Ilex Caprifoliaceae Lonicera (L) Ecology Z AQ R Z R R R R Z R Z Z Z AQ AQ R AQ R Z R Z Z R Z H R AQ R Z Z Z R Z R Z R Z a botanical affinities unclear but possibly with Polypodiaceae AQ = aquatic, swamp, and peat forming vegetation, R = riparian, Z = zonal (well-drained), H = halophyte (may also be part of R, Z), P = parasite, L = liana Material examined – Kizak 3043–22, 3043–23, 9187–10; Turtas 9187–93/1 Description Leaf fragments, venation parallelodromous with short perpendicular ‘veins’ connecting the main veins. Remarks Leaves of Typha are dorsiventral, up to 0.5 cm thick in living plants, parallel-sided, with many parallelodromous veins, crescentic on the outer surface, flat on the inner surface. The substance of lamina and sheath is made up of continuous columns of lacunae separated longitudinally by perpendicular partitions or diaphragms (Rowlatt and Morshead 1992). When strongly compressed, the imprints of these diaphragms appear as short ‘veins’ that are oriented perpendicular to the primary veins. This is the typical Typha pattern observed in fossil leaves and distinguishing such leaves from other large-leaved graminoids, such as Phragmites. Leaf remains of Typha latissima were figured from Miocene strata of Georgia and Ukraine (Kolakovski 1964; Iljinskaya 1968) and from late Oligocene strata of Kazakhstan (Kryshtofovich 1956). Typha is a characteristic element of the reed belt. In the Shish River site pollen sample Typha is rare (0.4%). Family Poaceae Barnhart 1895 Genus Phragmites Adans. 1763 Phragmites oeningensis A.Braun 1845 (Figure 4(f–g)) Phragmites oeningensis A.Braun – Braun 1845, p. 75 Phragmites oeningensis A.Braun – Iljinskaja 1968, p. 44, pl. 24, figs 1–3, pl. 44, figs 1, 2 Material examined – Kizak 9187–14; Turtas 3043–2, 9187–93/2 HISTORICAL BIOLOGY Table 3. Shish River site: Abundance of spores and pollen for individual plant groups based on 500 counted grains (see also Appendix 1). Organism Spore plant Spore plant Spore plant Spore plant Gymnosperm Gymnosperm Gymnosperm Gymnosperm Gymnosperm Gymnosperm Gymnosperm Gymnosperm Gymnosperm Gymnosperm Angiosperm herb Angiosperm herb Angiosperm herb Angiosperm herb Angiosperm herb Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Angiosperm woody Sum Taxon Laevigatosporites haardti Osmundaceae Leiotroletes Lycophyta Papillate Cupressaceae hiatus Papillate Cupressaceae Cathaya Pinus Haploxylon Pinus Diploxylon Abies Picea Larix Tsuga (small saccus) Tsuga (wide saccus, echinate) Potamogeton Typha Cyperaceae Poaceae Chenopodiaceae Fraxinus Liquidambar Fagus Quercus (not differentiated) Castaneoideae Myrica Carya Pterocarya Juglans Alnus Carpinus Betula Corylus Nyssa Ulmus Hemitrapa vel Trapa Ilex Eucommia Lythrum Symplocos Ericaceae Acer indet. Number 20 7 4 1 72 57 24 62 44 10 2 2 1 3 1 2 1 4 1 4 24 12 35 9 4 1 5 8 9 4 15 15 7 10 6 1 4 2 1 1 2 3 500 % 4.0% 1.4% 0.8% 0.2% 14.4% 11.4% 4.8% 12.4% 8.8% 2.0% 0.4% 0.4% 0.2% 0.6% 0.2% 0.4% 0.2% 0.8% 0.2% 0.8% 4.8% 2.4% 7.0% 1.8% 0.8% 0.2% 1.0% 1.6% 1.8% 0.8% 3.0% 3.0% 1.4% 2.0% 1.2% 0.2% 0.8% 0.4% 0.2% 0.2% 0.4% 0.6% 100% Description Leaf fragments with parallelodromous venation typical of Poaceae; stem fragments consisting of nodes and constricted internodes. Remarks Relatively wide leaves of this type are commonly produced by reed, Phragmites, a chief element of lakeshore vegetation. Nevertheless, based on the poorly preserved leaf and axis remains, it is impossible to assign them to a particular modern genus. Hence, we note that the fossil-species Phragmites oeningensis might include more than one monocot taxon. Order Proteales Juss. ex Bercht. et J.Presl 1820 Family Nelumbonaceae A.Rich. 1827 Genus Nelumbo Adans. 1763 Nelumbo protospeciosa Saporta 1891 (Figure 4(h–i)) Nelumbium protospeciosa Saporta – Saporta 1891, p. 17, pl. 1, figs 2, 3, pl. 4, figs 1, 2 Nelumbo protospeciosa Saporta – Takhtajan (ed.) 1974, pl. 32, figs 1–3 7 Nelumbo protospeciosa Saporta – Iljinskaja 1968, p. 63, pl. 3, fig. 8, pl. 19, figs 1, 2 Material examined – Shish 3043–47 (2 specimens) Description Leaf, simple, lamina orbicular, >11 cm in diameter, margin entire, main veins radiating from centre towards margin, branching before margin and forming loops. Remarks According to Zhilin (1989), this species might be of East Asian origin and migrated to Central Asia during the Paleogene. Nelumbo protospeciosa is known, for example, from Eocene deposits in Kamchatka (Budantsev 1997). The type locality for the species, Manosque, southern France (Figure 4(j)), is probably of late Oligocene age (Saporta de 1891; Mai 1995). The earliest fossil records of hardy types of Nelumbo producing tubers are from middle and late Eocene strata of East Asia (Li et al. 2014), from where this lineage migrated westwards during the later Paleogene and Neogene. In the Shish River site pollen sample Nelumbo is rare (a single grain was encountered). Order Saxifragales Bercht. et J.Presl 1820 Family Altingiaceae (Horan. 1841) Lindl. 1846 Genus Liquidambar L. 1753 Liquidambar europaea A.Braun ex Buckland 1836 (Figure 5(a)) Liquidambar europaeum A.Braun – Braun in Buckland 1836, p. 513. Liquidambar europaeum A.Braun – Braun 1845, p. 170. Liquidambar europaea A.Braun – Kovar-Eder et al. 2004, p. 58, pl. 2, figs 1–5. Material examined – Shish 3043–46 Description Leaf, simple, palmate, shallowly five-lobed, lobes triangular, lamina 5.5 cm long, 8 cm wide, base shallowly cordate, lobe apex acuminate, five main veins, margin finely crenate. Remarks Liquidambar europaea appeared in the Eocene of western North America/Beringia (Manchester 1999) and migrated to Central Asia and Europe during the Paleogene. Early Oligocene records are known both from Kazakhstan and Europe (Lai et al. 2018). According to Zhilin (1989), Liquidambar europaea was probably an east-Asiatic newcomer to Kazakhstan at the end of the Eocene. It became one of the most common plants in the Oligocene to Aquitanian floras of Kazakhstan. In the Shish River site pollen sample Liquidambar is abundant (4.8%). Order Rosales Bercht. et J.Presl 1820 Family Ulmaceae Mirb. 1815 Genus Ulmus L. 1753 Ulmus pyramidalis Göpp. 1855 (Figure 5(b–e)) Ulmus longifolia Unger – Unger 1847, p. 101, pl. 26, figs 5, 6 Ulmus pyramidalis Göpp. – Göppert 1855, p. 29, pl. 13, figs 10–12 Ulmus longifolia Unger – Güner et al. 2017, p. 131, pl. 11, fig. 5. Material examined – Kizak 3043–4, 3043–13, 3043–24, 3043–26, 9187–13, 9187–15, 9187–16 (2 specimens) 8 T. DENK ET AL. Figure 4. a, Salvinia sp., Kizak 3043 I-1-2, floating leaves with striate surface pattern. b, Coniferales leaf, Kizak 9187–25. c–e, Typha latissima A.Braun, leaf fragments, (c) Kizak 9187–10, (d) Kizak 3043/22, 23, (e) Turtas 9187–93/1. f–g, Phragmites oeningensis A.Braun, leaf fragments, (f) Turtas 3043–2, (g) Turtas 9187–93/2. h–j. Nelumbo protospeciosa Saporta, leaf fragments, (h) Shish 3043–47/1, (i) Shish 3043–47/2, (j), leaf from Manosque, France, late Oligocene, MNHN.F.13468. Scale bar 2 cm (a–j). HISTORICAL BIOLOGY 9 Figure 5. a, Liquidambar europaea A.Braun, leaf, Shish 3043–46. b–e, Ulmus pyramidalis Göpp, leaf fragments, (b) Kizak 3043–13, (c–d) Kizak 9187–16, (d) leaf margin detail, (e) Kizak 9187–15. Scale bar 2 cm (a–e). Description Leaf, simple, petiolate, petiole ca. 1–1.3 cm long, lamina elliptic, 5–7 cm long, 3–4 cm wide, lamina base asymmetrical, markedly asymmetrically auriculate, apex, acute, primary venation pinnate, secondary venation craspedodromous, 12–14 pairs of secondary veins, secondary veins occasionally branching in upper third, tertiary veins percurrent or branching, perpendicular to secondary veins, margin double serrate, main teeth served by secondary veins, subsidiary teeth served by abmedial veins. Remarks Ulmus longifolia Unger (Unger 1847), widely used for such slender leaves of elms (e.g. Güner et al. 2017) is an illegitimate name because it had earlier been used for an extant elm species from southeastern North America by Rafinesque (1836). According to Iljinskaja (1982) and Zhilin (1989), the species was present in Kazakhstan during the Burdigalian and in western Siberia during the Oligocene. In Europe, this species is relatively common during the middle and late Miocene (Hantke 1954; 10 T. DENK ET AL. Figure 6. a–f, Quercus pseudocastanea Göpp., leaf fragments, Kizak River site, (a) 9187–21, (b) 9187–22, (c) 9187–19, d 9187–25, (e) 3043–22, (f) 9187–23. Scale bar 2 cm (a–f). HISTORICAL BIOLOGY Knobloch 1969; Christensen 1976). In the Shish River site pollen sample Ulmus is infrequent (2%). Order Fagales Engler 1892 Family Fagaceae Dumort. 1829 Genus Quercus L. 1753 Quercus pseudocastanea Göpp. 1852 (Figure 6(a–f); 7A) Quercus pseudocastanea Göpp. – Göppert 1852, p. 276, pl. 35, figs 1, 2 Quercus pseudocastanea Göpp. – Iljinskaja 1982, p. 92, pl. 35, fig. 5, pl. 55, fig. 1, pl. 56, figs 1–4 Quercus pseudocastanea Göpp. – Walther and Zastawniak 1991, p.169, pl. 2, figs 2, 3, 5, 6 pl. 3, figs 1–6, text-fig. 8 Quercus pseudocastanea Göpp. – Kvaček et al. 2002, p. 63, pl. 13, figs 3–5, pl. 14, figs 1, 2, 4–6, pl. 15, figs 1, 4, 6, pl. 30, fig. 4 Material examined – Kizak 3043–22, 3043–27, 3043–28, 9187–10, 9187–19, 9187–21, 9187–22, 9187–23, 9187–25/1 Description Leaf, simple, petiolate, petiole to ca. 2 cm long, lamina elliptic or obovate, ca. 6–8 cm long, 4–6 cm wide, shallowly lobed, base rounded to asymmetrically cordate, apex acute, primary venation pinnate, primary vein stout basally, becoming thinner towards apex, secondary venation craspedodromous, number of pairs of secondary veins 4–8, rarely intersecondary veins present, tertiary venation percurrent or branched, tertiary veins perpendicular to secondary veins, forming a brochidodromous pattern in the lobe area, lobes triangular, lobe apex bluntly pointed. Remarks Lobed oaks of this type do not occur in Europe before the middle Miocene (Walther and Zastawniak 1991). This species is known from the Oligocene of Kazakhstan (Iljinskaja 1982) and thus might represent a lineage that spread westwards from East and/or Central Asia to western Eurasia in the Neogene (cf. Zhilin 1989 for other taxa showing this biogeographic pattern). Whereas Walther and Zastawniak (1991) suggested intrageneric relationships with section Cerris, Kvaček et al. (2002) noted closest anatomical similarities with Q. petraea (sect. Quercus). The only living species of Q. sect. Cerris comparable to the specimens from Kizak is the western Eurasian Quercus cerris L. The morphological variability in this species has recently been assessed (Denk et al. 2019). Based on the specimens from Kizak, we tentatively consider them to be more closely related to the white oaks, Q. sect. Quercus. Quercus cf. kubinyii (Kováts ex Ettingshausen 1852) Czeczott 1951 (Figure 7(b,c)) Castanea kubinyii Kováts – Kováts in Ettingshausen 1852, p. 6, pl. 1, fig. 12. Castanea kubinyii Kováts – Kováts in Ettingshausen 1853, p. 23, pl. 1, figs, 1, 2 Castanea kubinyii Kováts – Kováts 1856, p. 26, pl. 3, figs 1–7 Quercus kubinyii (Kováts) Czeczott – Czeczott 1951, p. 392, fig. 7 Quercus kushukensis Kornil. – Kornilova 1960, p. 38, pl. 1, fig. 10 pl. 2, fig. 9, pl. 3, figs 5, 7, 8, 12 pl. 8, fig. 13, pl. 13, figs 5–15, pl. 14, figs 1–16, pl. 18, fig. 8(b), pl. 19, figs 4–7(a), pl. 20, figs 1, 2, 3(a), 4–9, pl. 25, fig. 7, pl. 26, fig. 1, pl. 27, figs 1–10, pl. 28, figs 4, 5 Material examined – Shish 3043–48, 9187–49 11 Description Leaf, simple, petiolate, petiole 3 cm long, lamina elliptic, >6 cm long, 4–5 cm wide, base round, slightly auriculate, primary venation pinnate, secondary venation craspedodromous, margin dentate, teeth triangular, cuspidate, with bristle-like extensions of the secondary veins, basal side of teeth straight or sigmoid, apical side concave, tertiary veins perpendicular to secondary veins, percurrent or branched. Remarks Quercus kubinyii made its appearance in Europe in the early Miocene (Bůžek et al. 1996) and was abundant in western Eurasia during the middle and late Miocene (Walther and Zastawniak 1991; Kvaček et al. 2002). It belongs to Quercus sect. Cerris (Denk et al. 2017) and similar forms migrated from the Far East to Central Asia and Europe beginning in the early Oligocene. Quercus gigas Göpp., another fossil-species of sect. Cerris may produce leaves that morphologically overlap with those of Q. kubinyii (see e.g. Walther and Zastawniak 1991; Güner et al. 2017). This leaf type is not present in the late Oligocene Ashutas flora of Kazakhstan (Kryshtofovich et al. 1956) but occurs abundantly in the Burdigalian flora of Kushuk (Kornilova 1960; Zhilin 1989). In the Shish River site pollen sample Quercus is abundant (7%). SEM investigation revealed three different types of exine sculpture corresponding to three infrageneric groups; (i) exine with scattered microverrucae belonging to subgenus Cerris sect. Cerris (Figure 13(d–g)), (ii) exine microrugulate to weakly microverrucate belonging to subgenus Quercus sect. Protobalanus (Figure 13(h–j)), (iii) exine microverrucate belonging to subgenus Quercus excluding sect. Protobalanus (Figure 13(k–m); Denk and Grimm 2009b; Denk et al. 2017). Family Juglandaceae DC. ex Perleb 1818 Genus Pterocarya Kunth. 1824 Pterocarya paradisiaca (Unger 1849) Iljinsk. 1994 (Figure 7(d,e)) Prunus paradisiaca Unger – Unger 1849, p. 7, pl. 14, fig. 22 Pterocarya castaneifolia (Göpp.) Schlecht. – Kryshtofovich et al. 1956, p. 82, pl. 13, figs 6–8, pl. 17, figs 1–7, text-figs 29–31 Pterocarya paradisiaca (Unger) Iljinsk. – Iljinskaja 1994, p. 55, pl. 9, figs 4, 5, pl. 12, figs 1–4, pl. 13, figs 1–6, text-fig. 44: 1, 2 Material examined – Shish 3043–6 (2); Turtas 9187–4; Bicha 9187–94, 9187–95 Description Incomplete leaflets, lamina base shallowly cordate, slightly asymmetrical, lamina oblong to elliptic, >6 cm long, c. 3–4 cm wide, primary venation pinnate, secondary venation brochidodromous, forming additional loops towards margin from which small veins enter the teeth, leaf margin finely serrate, teeth with long basal and short apical side, ca. 5 teeth per 1 cm. Remarks The specimens investigated in the present study are very similar to the ones reported from the late Oligocene Ashutas locality (Kryshtofovich et al. 1956). Pterocarya paradisiaca had a long stratigraphic range in Europe from the late Oligocene to the Pleistocene. According to Zhilin (1989), this fossil-species appeared in Kazakhstan in the early Oligocene. In the Shish River site, pollen sample Pterocarya is infrequent (1%). 12 T. DENK ET AL. Figure 7. a, Quercus pseudocastanea Göpp., leaf fragment, Kizak 3043–27. b–c, Quercus kubinyii (Kováts) Czeczott, leaf fragments, (b) Shish 9187–49, (c) 3043–48. d–e, Pterocarya paradisiaca (Unger) Iljinsk., leaf fragments, (d) Turtas 9187–4, (e) Bicha 9187–94. f, Juglans zaisanica Iljinsk., leaf fragments, Bicha 3043/3. Scale bar 2 cm (a–f). HISTORICAL BIOLOGY 13 Figure 8. a–b, Alnus julianiformis (Sternberg) Kvaček & Holý, leaf fragments, (a) Shish 3043/6-1, (b) Turtas 3043/10-1. c, Alnus vel Corylus, leaf fragment, Shish 9187–96. d, Betula sp. Kizak 9187–12a. e. cf. Carpinus grandis Unger, leaf fragment, Kizak 9187–14. Scale bar 2 cm (a–e). Genus Juglans L. 1753 cf. Juglans zaisanica Iljinsk. ex Krysht. 1956 (Figure 7(f)) Juglans zaisanica Iljinsk. – Kryshtofovich et al. 1956, p. 85, pl. 16, fig. 3, text-fig. 32 Material examined – Bicha 3043–3, 3043–7, 9187–94 (partly) Description Leaflets, shortly petiolate, petiole bent, ca. 1 mm long, lamina incomplete, base asymmetrical, weakly auriculate, lamina narrow elliptic, primary vein stout, much thicker than secondary veins, secondary venation brochidodromous to eucamptodromous, margin entire. Remarks The few specimens at hand strongly resemble specimens of Juglans zaisanica described from the late Oligocene Ashutas locality (Kryshtofovich et al. 1956). This species is also known from middle Miocene deposits of Krynka (Kryshtofovich and Baikovskaya 1965). This fossil-taxon is very similar to the extant species Juglans regia L. In the Shish River site pollen sample Juglans is infrequent (1.6%). 14 T. DENK ET AL. Family Betulaceae Gray 1822 Genus Alnus Mill. 1754 Alnus julianiformis (Sternberg 1823) Kvaček & Holý 1974 (Figure 8(a,b)) Phyllites julianiformis Sternb. – Sternberg 1823, p. 37, pl. 36, fig. 2 Fagus feroniae Unger – Unger 1845, p. 106, pl. 28, figs 3, 4 Alnus feroniae (Unger) Czeczott – Iljinskaja 1968, p. 55, pl. 2, figs 1, 2, pl. 13, fig. 4, pl. 38, fig. 2, pl. 44, fig. 7 Alnus feroniae (Unger) Czeczott – Zhilin 1974, p. 35, pl. 13, figs 1, 2, pl. 34, figs 1–8 Alnus julianiformis (Sternberg) Kvaček & Holý – Kvaček and Holý 1974, p. 368, pl. 1–3, pl. 4, fig. 1, text-fig. 1 Alnus feroniae (Unger) Czeczott – Iljinskaja 1982, pl. 86, figs 2–6 Material examined – Shish 3043–6 (1); Turtas 3043–10 (2 specimens) Description Leaf, simple, petiolate, petiole 1 – >1.3 cm long, lamina ovate or elliptic, 3.5 – >5 cm long, 3–4 cm wide, base obtuse to bluntly acute, primary venation pinnate, primary vein stout, secondary venation craspedodromous, secondary veins sending off abmedial veins that enter into bristle-like, small teeth, tertiary veins percurrent or branched, perpendicular to secondary veins. Remarks This species is based on material from early Miocene strata of Bílina (Bohemia) and has a stratigraphic range in Europe from early Miocene to Pliocene. It occurs in riparian and mixed mesophytic forests (Kvaček and Holý 1974). In Kazakhstan, it occurred during the Aquitanian (Iljinskaya 1982). In the Shish River site pollen sample Alnus is infrequent (1.8%). Alnus vel Corylus sp. (Figure 8(c)) Material examined – Shish 9187–96 (2 leaf imprints) Description Leaf, lamina roundish, petiolate, petiole >0.3 cm long, lamina 7 cm long, 5–6 cm wide, one fragment of a larger leaf >9 cm wise, base shallowly cordate to obtuse, apex obtuse, number of secondary veins 7–8, basal secondary veins with abmedial veins, basal secondary veins forming wide angles, apical secondary veins forming acute angles with primary vein, margin only fragmentary preserved, tertiary veins perpendicular to secondary veins, percurrent or branched, outermost tertiary veins sending small veinlets into teeth. Remarks This leaf type either belongs to Alnus or Corylus. The overall leaf shape and venation close to the margin match both genera, the presence of several abmedial veins in the lower part of the lamina fits well with Corylus. We note some similarity with the late Oligocene species Corylus jarmolenkoi Grub. From Ashutas (Kryshtofovich et al. 1956). The small number of specimens and poor state of preservation do not allow a more exact determination. In the Shish River site pollen sample Corylus is common (3%). Genus Betula L. 1753 Betula sp. (Figure 8(d)) Material examined – Kizak 9187–12a, 12b (part and counter-part) Description Leaf, upper portion of leaf blade, 3 cm long, 4 cm wide, secondary venation craspedodromous, tertiary venation percurrent or branched, perpendicular to secondary veins, margin compound serrate, secondary vein terminating in primary tooth, abmedial vein ending in secondary tooth, tooth apical and basal side slightly sigmoid, tooth apex appearing glandular. Remarks Based on its compound serrate leaf margin this leaf remain probably belongs to Betula. In the Shish River site pollen sample Betula is common (3%). Genus Carpinus L. 1753 cf. Carpinus grandis Unger 1850 (Figure 8(e)) Carpinus grandis – Unger 1850, p. 408. Carpinus grandis Unger – Heer 1856, p. 40, pl. 62, figs 12, 13, 15, 15b Material examined – Kizak 9187–14 Description Leaf, simple, petiolate, petiole ca. 6 mm long, lamina ca. 5.4 cm long, ca. 2.3 cm wide, ovate, 11–12 pairs of secondary veins, secondary venation and margin not well preserved. Remarks A single poorly preserved leaf appears to be Carpinus. Since details of the leaf margin are not preserved, the leaf is difficult to assign to a particular fossil-species. Further, we cannot exclude that this leaf belongs to another genus in the Fagales, such as, for example, Carpinus. In the Shish River locality pollen sample Carpinus is infrequent (0.8%). Order Malpighiales Juss. ex Bercht. et J.Presl 1820 Family Salicaceae Mirb. 1815 Genus Populus L. 1753 Populus balsamoides Göpp. 1855 (Figure 9(a); 10A) Populus balsamoides Göpp. – Göppert 1855, p. 23, pl. 15, figs 5, 6 Populus emarginata Göpp. – Göppert 1855, p. 23, pl. 15, figs 2–4 Populus eximia Göpp. – Göppert 1855, p. 23, pl. 16, figs 3–5, pl. 17, figs 1–3 Populus ovalis Göpp. – Göppert 1855, p. 23, pl. 16, fig. 1 Populus balsamoides Göpp. – Heer 1856, p. 18, pl. 60, figs 1–3, pl. 63, figs 5, 6 Material examined – Shish 3043–9, 3043–19, 9187–42, 9187–58 Description Leaf, simple, petiolate, lamina roundish ovate, 6–10 cm long, 6–10 cm wide, primary venation pinnate, 5–6 pairs of secondary veins, basal pair of secondary veins with abmedial veins, opadial HISTORICAL BIOLOGY 15 Figure 9. a, Populus balsamoides Göpp. leaf fragment, Shish 3043–9. b, Populus glandulifera Heer, leaf fragment, Kizak 9187–17. c–d, Populus latior A.Braun, leaf fragments, (c) Shish 3043–15, (d) Shish 3043–39. e, Populus sp., bract, Shish 3043–37. Scale bar 2 cm (a–d) and 0.5 cm (e). 16 T. DENK ET AL. Figure 10. a, Populus balsamoides Göpp. leaf fragment, 3043–19 Shish. b, Salix lavateri A.Braun, leaf, Kizak 9187–25a. c–e, Hemitrapa praeconocarpa (V.N.Vassil) Budantsev, fruit compressions and imprints, (c) Shish 9187–36, (d) Shish 3043–31, (e) Shish 3043–30. Scale bar 2 cm (a–e). vein present, secondary venation brochidodromous, margin finely crenate, small veins departing from loops formed by secondary/ abmedial veins serving crenulated teeth, teeth with blunt apex and sinus, apical side with inconspicuous glandular thickening. margin and sending small veins into the teeth, secondary veins strongly bent, four pairs of secondary veins per lamina side, intersecondary veins present, margin crenate, teeth inconspicuous, glandular. Remarks Populus balsamoides was present in Kazakhstan during the early to late Oligocene. In the late Oligocene flora of Karashasor (Karasor) it co-occurs with Liquidambar europaea, Pterocarya paradisiaca, Ulmus carpinoides, and Alnus feroniae among others (Zhilin 1989). Remarks Hantke (1954) treated Populus glandulifera as synonym of P. latior arguing that the mere presence of distinct glands was not sufficient to warrant species status for such leaves. In addition, he noted that in the modern balsam poplar species group, such glands are not constant. We follow Iljinskaya (1982) and keep this taxon separate from P. balsamoides. Populus glandulifera Heer 1856 (Figure 9(b)) Populus glandulifera Heer – Heer 1856, p. 17, pl. 58, figs 6, 7, 10 Material examined – Kizak 3043–18, 9187–17, 9187–18 Populus latior A.Braun ex Buckland 1836 (Figure 9(c,d)) Description Leaf, simple, petiolate, petiole stout, flattened, preserved along 3 cm, prominent glands on petiole and basal lamina at attachment point to lamina, lamina broad ovate, ca. 9 cm long, 10 cm wide, primary venation pinnate, secondary venation brochidodromous, abmedial and secondary veins forming loops close to the lamina Phyllites populina Brongn. – Brongniart 1822, p. 237, pl. 3, fig. 4 Populus latior A.Braun – Braun in Buckland 1836, p. 512 Populus latior A.Braun – Braun 1845, p. 169 Populus latior A.Braun – Heer 1856, p. 11, pl. 53–57 Populus populina (Brongn.) Erw.Knobloch – Knobloch 1964, p. 601 nom. illeg. non Populus populina Jarm. – Jarmolenko 1935, p. 16 HISTORICAL BIOLOGY Populus populina (Brongn.) Erw.Knobloch – Knobloch 1968, p. 128 Populus populina (Brongn.) Erw.Knobloch – Kvaček et al. 2002, p.82, pl. 21, figs 1–5 Material examined – Shish 3043–14–18, 3043–20, 3043–21, 3043–35, 3043–36, 3043–39–45, 9187–52–55, 9187–59–86 Description Leaf, simple, petiolate, petiole stout, flattened, preserved part 2–3 cm long, lamina broad ovate to nearly round, 5–9.5 cm long, 5–10 cm wide, base wide obtuse, caudate, or cordate, apex acute to acuminate, primary venation pinnate, two basal lateral veins thicker than following secondary veins approaching in thickness the primary vein (pseudoactinodromous), several abmedial veins departing from basal lateral and secondary veins, branching or forming loops from which higher order veins enter the teeth, secondary veins brochidodromous/semicraspedodromous, occasionally intersecondary veins present, tertiary veins percurrent, perpendicular to secondary veins, margin dentate, teeth fine to coarse, triangular to hooked, with blunt glandular apex. Remarks It has been widely accepted that P. latior is a junior synonym of P. populina as the basionym for the latter, Phyllites populina was published earlier than Braun’s (1845) valid publication of P. latior (Knobloch 1964). Recently, Doweld (2017) proposed to resurrect the name Populus latior over P. populina as this name had earlier been used for Cretaceous leaf remains by Jarmolenko in 1935. We follow Doweld (2017) and use the name P. latior. Pollen of Populus was not encountered in the Shish River site pollen sample. Pollen of Populus has low fossilisation potential because its exine does not form a continuous cover of sporopollenin (Rowley and Erdtman 1967) and is poorly preserved even in Quaternary sediments (Cushing 1967). Populus sp. (Figure 9(e)) Populus latior A.Braun – Heer 1856, p. 10 Populus sp. – Hantke 1954, p. 53, pl. 4, fig. 3 Material examined – Shish 3043–37 Description Floral bract, roundish, ca. 0.5 cm long, 0.5 cm wide, apex deeply cut, segments serrate. Remarks The roundish floral bracts are closely similar to the extant species P. tremula L. with a vast range across Eurasia. Genus Salix L. 1753 Salix lavateri A.Braun ex Stitzenberger 1851 emend. Hantke 1954 (Figure 10(b)) Salix lavateri A.Braun – Braun in Stizenberger 1851, p. 78 Salix lavateri A.Braun – Heer 1856, p. 28, pl. 66, figs 1–12 Salix denticulata Heer – Heer 1856, p. 30, pl. 68, figs 1–4 Salix varians Göpp. – Heer 1859, p. 174, pl. 150, fig. 6 Salix lavateri A.Braun – Hantke 1954, p. 55, pl. 5, figs 2–16 Material examined – Bicha 3043–7 (2 specimens), Kizak 9187–25/2 17 Description Leaf, simple, petiolate, narrow elliptic to lanceolate, 12 cm long, 2 cm wide, base acute, apex elongated acute, primary venation pinnate, secondary venation eucamptodromous, intersecondary veins present, secondary veins strongly bent, departing from midvein at nearly right angles, then bending towards margin and running parallel with margin, margin entire or distinctly crenate, teeth with glandular tip. Remarks The three leaves in our collection differ in leaf margin. The few leaves from the Bicha River site could represent a different willow species than the single leaf from the Kizak River site. We follow Hantke (1954) and include crenate and entire margined specimens within a single fossil-species Salix lavateri. In the Shish River site pollen sample Salix is infrequent (0.8%). Order Myrtales Juss. ex Bercht. et J.Presl 1820 Family Lythraceae J.St.-Hil. 1805 Genus Hemitrapa Miki 1948 Hemitrapa praeconocarpa (V.N.Vassil. 1949) Budantsev 1960 (Figure 10(c–e)) Trapa praeconocarpa Vassilijev – Vassilijev 1949, p. 639 Trapa sp. – Kryshtofovich and Borsuk 1939, p. 393, pl. 4, fig. 17, pl. 6, figs 1–3 Trapa praeconocarpa V.N.Vassilijev. – Baranov 1954, p. 355, pl. 165, figs 7–9 Hemitrapa praeconocarpa (V.N.Vassilijev.) Budantsev – Budantsev 1960, p. 143 Material examined – Turtas 3043–29, Shish 3043–30, 3043–31, 3043–32, 9187–36, 9187–39 Description Fruits, rhombic in cross-section, 1.5–3 cm long, with a single pair of arms originating in the middle of the fruit, arms horn-like, tapering in a sharp apex, stalk (preserved part) short, ca. 0.2–0.4 cm. Remarks Budantsev (1960) referred Miocene specimens from the Irtysh River, Western Siberia, previously assigned to Trapa by Vassiljev (1949) to Hemitrapa. Fossil records of Hemitrapa from Miocene strata in Eurasia can be divided into two morphological types, one with a single pair of arms and another with two pairs of arms (Wang 2012; Su et al. 2018). Among the species with a single pair of arms, the specimens described here closely match the description of H. praeconocarpa in Wang (2012). In the Shish River site pollen sample Hemitrapa vel Trapa is infrequent (1.2%). Order Malvales Juss. ex Bercht. et J.Presl 1820 Family Malvaceae Juss. 1789 Genus Byttneriophyllum Givulescu ex Erw.Knobloch & Kvaček 1965 Byttneriophyllum tiliifolium (A.Braun) Erw.Knobloch & Kvaček 1965 (Figure 11(a), B; 12A) Cordia tiliaefolia A.Braun – Braun 1845, p. 170 Dombeyopsis tiliaefolia (A.Braun) Unger – Unger 1850, p. 44, pl. 25 (46), figs 1–3 (?), 4, 5 Dombeyopsis grandifolia Unger – Unger 1850, p. 45, pl. 26 (47), figs 1, 2, pl. 27 (48), figs 1, 2 18 T. DENK ET AL. Figure 11. a–b, Byttneriophyllum tiliifolium (A.Braun) Erw.Knobloch & Kvaček, (a) leaf imprint, Turtas 9187–2:VI-25-3 Turtas, (b) leaf fragment, Bicha 3043–8. c, Hydrangea (Platycrater) iljinskajae spec. nov., leaf fragment, Shish 3043–11 Shish. Scale bar 2 cm (a–c). Ficus tiliaefolia (A.Braun) Heer – Heer 1856, p. 68, pl. 83, fig. 3 (?), 6–8, 9 (?), 10, 11, 12 (?), pl. 84, figs 1–5 Alangium aequalifolium (Göpp.) Krysht. & Bors. – Kryshtofovich and Borsuk 1939, p. 390, pl. 5, figs 1–8, pl. 6, figs 6, 7, text-figs 1–8 Byttneriophyllum tiliifolium (A.Braun) Erw.Knobloch & Kvaček – Knobloch and Kvaček 1965, p. 128, pl. 1, pl. 2, pl. 3, pl. 4, pl. 5, pl. 6, figs 1–4 Alangium tiliifolium (A.Braun) Krysht. – Iljinskaja 1968, p. 81, pl. 6, fifs 2–11, pl. 18, fig. 1, pl. 24, fig. 4, pl. 26, fig. 1, HISTORICAL BIOLOGY 19 Figure 12. a, Byttneriophyllum tiliifolium (A.Braun) Erw.Knobloch & Kvaček, leaf fragment, 9187–2: I-25-I Kizak. b, Fam., gen. et spec. indet 1, leaf fragment, Turtas 3043–10. c, Fam., gen. et spec. indet 2, leaf fragment, Kizak 9187–25/1. Scale bar 2 cm (a–c). pl. 27, fig. 6, pl. 33, fig. 9, pl. 42, fig. 5, pl. 47, fig. 1, pl. 48, figs 6, 7, pl. 49, figs 1–7, pl. 50, pl. 51, fig. 5, text-fig. 11 Material examined – Bicha 3043/8; Kizak 3043–25; Turtas 9187–2:VI-25-2a, VI-25-2b, VI-25-3 Description Leaves, simple, petiolate, petiole not preserved along its entire length, point of petiole attachment to lamina swollen, lamina roundish-ovate, 7–11 cm long, 7–11 cm wide, apex bluntly acute, basis strongly asymmetrical, shallowly cordate, venation actinodromous, three main veins, secondary venation brochidodromous, main veins and secondary veins forming loops close to the leaf margin, basal primary and secondary veins with abmedial veins, these forming loops close to the leaf margin, tertiary veins branched or percurrent, perpendicular to main, secondary, and abmedial veins, leaf margin entire. Remarks The specimens in our material correspond to the type material of the species from middle Miocene deposits of Öhningen. Byttneriophyllum tiliifolium was a typical element of swamp forests in the Neogene of western Eurasia (Worobiec et al. 2010) where it co-occurred with lignite forming conifers such as Glyptostrobus and deciduous broadleaved angiosperms such as Acer, Alnus, Betula, Cercidiphyllum, Populus, Salix and others (Worobiec et al. 2010). According to Knobloch and Kvaček (1965), Byttneriophyllum tiliifolium is an element of the ‘ArctoTertiary deciduous Turgay floral complex’ and migrated from Northeast Asia to Europe via Siberia during the Cenozoic (see also Zhilin 1989). Order Cornales Link 1829 Family Nyssaceae Juss. ex Dumort. 1829 Genus Nyssa L. 1753 cf. Nyssa sibirica Dorof. 1963 Nyssa sibirica Dorof. – Dorofeev 1963, p. 237, pl. 41, figs 1–4 Nyssa sibirica Dorof. – Zhilin 1989, p. 267, figs 19A, B Material examined – Shish 3043–33, 3043–34 Description Endocarp, outline oblong, elliptic, ca. 7.5 mm long, 4 mm wide, latitudinal grooves. Remarks The specimens at hand are covered by a thick layer of varnish and hence difficult to observe. By their shape and size, however, we tentatively refer them to Nyssa sibirica. This species was described from Oligocene strata at the Kozyulino site near the confluence of the Rivers Tom and Ob, (Zhilin 1989). In the Shish River site pollen sample Nyssa is infrequent (1.4%). Family Hydrangeaceae Dumort. 1829 Genus Hydrangea Gronov. 1753 s.l. (Platycrater Siebold & Zucc. 1838) Hydrangea (Platycrater) iljinskajae spec. nov. (Figure 11(c)) Diagnosis Leaf simple, pinnate, lamina size nothophyll, lamina elliptic, base acute, apex acute to acuminate, secondary venation weak brochidodromous to eucamptodromous, apical part of secondary veins running parallel to leaf margin, margin sharply dentate, teeth awlshaped, distinctly acute, tertiary veins oblique to secondary and intersecondary veins, percurrent or branched. Holotype – Designated herewith, specimen 3043–11 Shish Etymology – Referring to late palaeobotanist Irina Alekseevna Iljinskaja (1921–2011) Stratigraphy – Late Oligocene (Chattian), Zhuravka Horizon, Turtas Formation Type locality – Shish River, Omsk oblast, Russia Material examined – Shish 3043–11 20 T. DENK ET AL. Description Leaf, simple, lamina elliptic, ca. 13 cm long, ca. 5 cm wide, base acute, apex acute to acuminate (apical part of apex missing), primary venation pinnate, secondary venation weak brochidodromous to eucamptodromous, with parallel and upturned secondary veins, upper parts of secondary veins running parallel with margin and sending off small veinlets into the teeth, intersecondary veins present, tertiary veins percurrent or branched, in some places approaching a reticulate pattern, oblique to secondary veins, margin dentate, teeth small (ca. 1 mm), sharp, awlshaped, with straight to slightly convex basal sides and straight to slightly concave apical sides, teeth oriented perpendicular to leaf margin or apically. Remarks Tooth architecture is most similar to the extant Japanese shrub species Platycrater arguta Siebold & Zucc. Recent molecular phylogenetic work has shown that Hydrangea is highly polyphyletic (e.g. De Smet et al. 2015). According to Angiosperm Phylogeny Website (http://www.mobot.org/MOBOT/research/APweb/), ‘generic limits around Hydrangea were a mess – Platycrater and seven other genera are embedded in Hydrangea s. str.’ However, although these genera have been embedded within Hydrangea and a revised sectional classification was provided (De Smet et al. 2015) some authors prefer narrower generic limits based mainly on morphological and ecological grounds (Ohba and Akiyama 2016). Thus, we here use the extended genus Hydrangea but indicate closest similarities with only a small fraction of the genus, the former genus Platycrater, by indicating the old genus name in brackets for the new fossil-species. The extant species P. arguta occurs in Japan and China (Ohwi 1965; Wu and Raven 2001). In Japan it occurs at low elevations (up to 500 m a.s.l.; GBIF, https://www.gbif.org/species/ 7318947) while in China it occurs from 400 to 1800 m a.s.l. in sparse forests or thickets in valleys, on stream banks and mountain slopes (Wu and Raven 2001). Platycrater thrives under humid warm temperate climates (Köppen-Geiger climate types Cfa and Cfb; Kottek et al. 2006; Appendix 3). Similar leaf remains have been reported from early Miocene strata of Bohemia as Symplociphyllum hradekense Kvaček & Bůžek (Kvaček and Bůžek 1966; Knobloch and Kvaček 1976). In this species, the secondary veins are very similar to Hydrangea iljinskajae and send off small veinlets into the sharp teeth. However, the teeth in Symplociphyllum commonly are more bristle-like than in our species. Incertae sedis Fam., gen. et spec. indet 1 (Figure 12(b)) Material examined – Turtas 3043–10 Description Leaf or leaflet, lamina ovate elliptic, 3.2 cm long, 1.7 cm wide, base wide acute, apex acute, primary venation pinnate, secondary venation brochidodromous to semicraspedodromous, leaf margin serrate, teeth served by small veinlets departing from loops of secondary veins, teeth rosoid. Remarks The single specimen at hand resembles leaflets of the family Rosaceae; particularly as found in the genus Rosa. Fam., gen. et spec. indet 2 (Figure 12(c)) Material examined – Kizak 9187–25/1 Description Apical leaf fragment, 2 cm long, 1 cm wide, representing the acute apical part of a leaf or lobe of a leaf, secondary venation semicraspedodromous, margin simple dentate, teeth with long straight basal side, and short apical side. Remarks The single specimen at hand is too fragmentary for a meaningful taxonomic assessment. Discussion Taxonomic composition, palaeoenvironments, taphonomy The majority of macrofossils recovered from the four sites represent riparian, swamp and aquatic communities (Table 1). From the Bicha River site, only four taxa are known, comprising Salix, Pterocarya, Juglans and Byttneriophyllum. This is indicating a lakeshore or riparian vegetation possibly exposed to temporal flooding (Salix). The Turtas River assemblage comprises reed (Phragmites) and aquatic plants (Hemitrapa) together with riparian elements (Alnus, Byttneriophyllum, Pterocarya, cf. Rosa/Rubus). The Kizak River site is more diverse and comprises reed plants such as Phragmites and Typha, aquatic plants (Salvinia), and riparian and swamp forest elements such as Byttneriophyllum, Salix, and Populus glandulifera. In addition, some taxa might have formed part of well-drained stands behind the riparian vegetation (Ulmus, Quercus pseudocastanea and Carpinus grandis). The Shish River site represents two-thirds of all the studied specimens and is dominated by Populus latior. This riparian element is joined by P. balsamoides, Nyssa and Liquidambar. Alnus julianiformis might have also been part of this riparian vegetation but likely also formed part of the zonal vegetation further away from the lake (Kvaček and Holý 1974). Aquatic plants from this site (Nelumbo, Hemitrapa) indicate a lake. Nelumbo protospeciosa is only known from this site and is a western Siberian Miocene endemic species according to Wang (2012). The Shish River site also yielded plants attributable to the zonal hinterland vegetation. Besides Alnus julianiformis, Quercus kubinyii and the newly described Platycrater iljinskajae may have been part of the hinterland vegetation as well. In general, the leaf and fruit assemblages of all four sites are dominated by riparian and aquatic elements suggestive of communities in and adjacent to a large water body. This suggests a taphonomic filter as would be expected for leaf fossils (cf. Bouchal et al. 2020). For example, whereas poplar leaves are the most abundant element among our plant fossils, Alnus julianiformis, Carpinus, and Platycrater are represented by few or single leaves, suggesting transport from a distant source. In case of Carpinus, the poor state of preservation suggests transport from further away. The Shish River site is most diverse in plant macrofossils and differs from the other three locations by the high number of Populus latior leaves and the presence of Platycrater iljinsjkayae. Byttneriophyllum is shared by the Kizak, Bicha and Turtas River sites. Among these sites, only Kizak is fairly rich in species and is distinguished from all other sites by the moderate abundance of Ulmus pyramidalis and Q. pseudocastanea leaves. The palynoflora from the leaf-bearing layer of the Shish River site is dominated by woody gymnosperms and angiosperms (55.4% and 36.4%, respectively). Spore producing plants (6.4%) and HISTORICAL BIOLOGY herbaceous angiosperms (1.8%) are less common (Appendix 2). In general, the palynoflora is much more diverse than the leaf assemblage and captures a more diverse vegetation surrounding the palaeolake (Table 2). Most eye-catching is the high abundance and diversity of conifers (needleleaf evergreen and deciduous biomes according to Woodward et al. 2004), which comprise both Cupressaceae (25.8%) and Pinaceae (29.6%; Table 3). It is remarkable, that the macrofossil record is almost void of conifer leaves and reproductive structures, whereas conifers are the most prominent elements in the pollen record (Tables 1–3, Appendix 2). Some of these are typical elements of waterlogged habitats, whereas others are typically growing on well-drained soils (e.g. Larix, Abies). Hence, some relief is to be expected for the source area of the recovered plant fossils. This relief might have corresponded to a mosaic of lowland swamps with peat formation, floodplains, natural levees, and hammocks (Ferguson et al. 1999). Among angiosperms (broadleaf deciduous biome of Woodward et al. 2004), riparian elements are well-represented. These were typical elements of lowland forests dominated by Quercus and Juglandaceae. Typical streamside plants (Liquidambar, Nyssa) may have been interspersed in these forests as well. Finally, welldrained areas were covered by mixed broadleaf forests and mixed broadleaf and conifer forests. These contained Fagus, Eucommia, Carpinus, Betula, Corylus, Quercus sect. Cerris, and very likely Quercus sect. Quercus (Table 2). The biomes recognised in the present study correspond closely to the forest assemblages recognised for the Oligocene to early Miocene in Western Siberia based on carpological data (Nikitin 2006; Popova et al. 2019a) and based on palynological data (Arkhipov et al. 2005; Volkova et al. 2016). Age constraints provided by leaf fossils It is difficult to establish the precise age of the four leaf assemblages described here. However, building on the work by Zhilin (1974, 1989)), a rough stratigraphic framework – bearing in mind that several of the ‘Aquitanian’ leaf assemblages from the North Ustyurt and North Aral regions actually may be Chattian (see Material and Methods section) – can be suggested. For example, according to Zhilin (1989), three fossil-species, Eucommia palaeoulmoides, Alnus feroniae, and Juglans zaisanica existed in western Kazakhstan only during the early Miocene (Aquitanian) and Byttneriophyllum (as Alangium) existed north of the Aral Sea during the Aquitanian (the localities from which Byttneriophyllum has been reported are of Chattian age in the revised stratigraphic framework as outlined above). While Eucommia is part of the palynoflora of Shish, the other three species are part of the leaf assemblage. Among species, confined to the late Oligocene to early Miocene in western Kazakhstan, Zhilin (1989) lists Fagus antipofii, and among those ranging from early Oligocene to the beginning of the early Miocene, Nelumbo protospeciosa, Liquidambar europaea, Populus balsamoides, and Pterocarya paradisiaca are part of the leaf assemblages described here. In case of Quercus pseudocastanea that is part of the Kizak River site, we note that this species is confined to middle Miocene to late Pliocene floras in Europe (Walther and Zastawniak 1991). In contrast, oldest fossils that might belong to Quercus pseudocastanea are from late Oligocene deposits of Ashutas (northeastern Kazakhstan; Kryshtofovich et al. 1956; Iljinskaya 1982). Quercus pseudocastanea has also been reported from early Miocene deposits of western Siberia (Kozhevnikovo, Tomsk oblast; Yakubovskaya 1957). Macrofloras with lobed oaks most likely belonging to Quercus sect. Quercus also occur in the early Oligocene of Kiin Kerish (Iljinskaya 1991) with forms resembling the East Asian Q. serrata (sect. Quercus) and the early Oligocene of the Far East (Denk et al. 21 2017). The other Quercus species in our material, Q. kubinyii from the Shish River site, clearly belongs to a lineage of Quercus sect. Cerris that commenced in Northeast Asia during early Oligocene and possibly Eocene times (Pavlyutkin 2015; Denk et al. 2017; Naryshkina and Evstigneeva 2020). This species is not known from Europe prior to the Miocene (Teodoridis and Kvaček 2006). Early Miocene leaf types described as Q. kuschukensis (Kornilova 1960; Iljinskaya 1982) from northern Kazakhstan may partly belong to this species but would need to be reinvestigated. In general, when considering leaf fossils greatest similarities of the four localities investigated in this study are with leaf floras of northern Kazakhstan and Southwestern Siberia that have variously been assigned to early Miocene or late Oligocene (Gorbunov 1957; Yakubovskaya 1957; Zhilin 1974, 1989, 2001) and less so with late Oligocene floras (e.g. Kumsuat; Zhilin 1989). In view of the revised stratigraphy of strata from the North Ustyurt and North Aral regions previously believed to be Aquitanian by Zhilin (1989) but currently considered late Oligocene, it is difficult to make the distinction between Chattian and Aquitanian based on the present leaf material. However, considering that the Shish River site is Chattian in age based on its spore and pollen assemblage (see below) and the Turtas River site is located close to palynological sections that are dated as Chattian as well (Volkova et al. 2016), we consider these macrofossil sites to be of late Oligocene age. Nearby palynological sections are also available for the Kizak River site (see Masali section in Kuz’mina et al. 2019). The spore-pollen assemblage from this section is dominated by Chlorophyta and Betulaceae along with Pinaceae and moderate amounts of herbaceous taxa and is considered to be late Miocene in age. This age can be ruled out for the Kizak River site leaf assemblage, but the abundant leaves of Quercus pseudocastanea and Ulmus pyramidalis plus the rare occurrence of Betula make this site distinct from the other leaf sites studied. This leaf assemblage might correspond to the Alnus-Betula-Quercus sibirica-Ulmus crassa spore-pollen assemblage of Volkova et al. (2016), which corresponds to the lower Abrosimovka Formation (Figure 3). It is noteworthy that marked similarities are also with middle Miocene leaf floras of Eastern Europe (Kutuzkina 1964; Ilyinskaya 1968) although the latter are much more diverse. Age constraints provided by dispersed spores and pollen A more precise stratigraphic framework can be proposed for the Shish River site based on the composition and abundance of the investigated palynoflora (Table 3; Appendix 2). Arkhipov et al. (2005) reviewed the Paleogene and Neogene vegetation history of Western Siberia using palynological data. We found a close correlation with the pollen flora from the Shish River locality investigated in the present study and the palynocomplex of the Turtas Formation (Turtasskaya suite) coinciding with the late Oligocene Turtas Lake. The upper Oligocene Zhuravka Horizon (including the Turtas and Zhuravka formations is characterised by local pollen assemblages in which taxodiaceous (papillate) Cupressaceae and Pinaceae dominate. In addition, Fagaceae pollen (Quercus, Fagus) dominate among angiosperms along with Juglandaceae and Betulaceae. As newly arriving taxa, warm temperate elements such as Liquidambar, Ilex, Nyssa, and Symplocaceae are mentioned (Arkhipov et al. 2005). A number of palynological investigations provide further information, which helps constraining the age of the Shish River site. From the stratotype horizon of the Zhuravka Horizon (including the Zhuravka and Turtas formations; Zashchitino Village, north of Tobolsk, Figure 1(a)), Volkova et al. (2016) described a palynological section that shows similar ratios of spores, 22 T. DENK ET AL. gymnosperms, and angiosperms with the Shish River locality. It also shares the high proportions of Pinaceae and taxodiaceous (papillate) Cupressaceae and very low abundance of herbaceous angiosperms. However, Fagaceae, which are common both in the macrofossil record and pollen record of the Shish River site, are rare in the Zashchitino profile. Similar results were reported by Oreshkina et al. (2020), who investigated palynomorphs from borehole Zyryanskaya-1 belonging to the Turtas Formation in the southwestern part of the Tyumen Region. Here, gymnosperms reached up to 85–90%, Juglandaceae are prominent among angiosperms, while Fagaceae are entirely missing. Hence, the assemblage of pollen and spores differs from other assemblages of the Turtas and Zhuravka formations by the low amounts of papillate Cupressaceae and the absence of Fagaceae. Oreshkina et al. (2020) explained this deviation from the common pattern by regional environmental differences and/or different levels of transgressions during the late Oligocene. Additional sections from boreholes including early Oligocene to middle Miocene layers were investigated from the region south of Omsk (Figure 1(g,h); Kuzmina and Volkova 2001, 2008). For the early Oligocene strata, we note similarities in the pollen spectra of Pinaceae and taxodiaceous (papillate) Cupressaceae, as well as the low percentages of herbaceous angiosperms. A significant difference of the early Oligocene pollen assemblages with the Shish River locality is the presence of extinct Fagaceae (‘Quercus’ gracilis and ‘Q.’ graciliformis), which are typical of Eocene and early Oligocene deposits across Eurasia and absent from the Shish River site (Figure 13). Likewise, early Miocene deposits of the Beshcheul Formation, also similar in taxonomic composition with the Shish River site, differ considerably in the proportion of key taxonomic groups. Late early and early middle Miocene spore-pollen assemblages contain considerable amounts of Polypodiaceae and Alnus and moderate abundance of herbaceous angiosperms. In contrast, late Oligocene and early Miocene assemblages are more similar to the Shish River site assemblage, both in terms of the frequency of spores, gymnosperms, and angiosperms, as well as in the proportions of key taxonomic groups (Pinaceae, taxodiaceous/papillate Cupressaceae, woody angiosperms with prominent Quercus and Fagus, low proportion of herbaceous angiosperms). This corresponds to the ‘Quercus sibiricaFagus grandifoliiformis-Pinaceae’ palynoassemblage (Kuz’mina and Volkova 2008). Further high similarities are encountered between the Shish River site palynoflora and the assemblages from borehole 8 close to the border with Kazakhstan (Gnibidenko et al. 2011; Figure 1(b)). Here, the assemblages of the Zhuravka Formation are nearly identical with the assemblage of the Shish River locality, whereas the younger ones from the early Miocene Beshcheul Formation differ markedly by higher amounts of herbaceous angiosperms. Popova et al. (2019b) described a palynoflora from Kumyrtas, central Kazakhstan, characterised by high percentages of Betula (ca. 30%) and Fagus (ca. 15%) along with abundant Pterocarya (7.5%). The age of this flora was considered Aquitanian based on floristic similarity with the Nausha (leaf) flora (southern Kostanay Region). The Nausha flora, in turn, had been dated as Aquitanian by the occurrence of the genus Paraceratherium and by correlation with marine molluscs from the northern Ustyurt Plateau to the west (Zhilin 1989). It remains unclear to us how the Kumyrtas (fruits and seeds, and spore-pollen) assemblage was correlated with the Nausha (leaf) assemblage, but if this correlation is correct, the age of the Kumyrtas assemblage should be Chattian in view of the revised stratigraphy of the North Ustyurt and North Aral region based on marine molluscs, micromammals and the Paraceratherium stratigraphic range (see Material and Methods section). The pollen record would indicate that this assemblage belongs to the Pterocarya stenopteroides-Fagus grandifoliiformis pollen zone (Kuz’mina and Volkova 2008; Gnibidenko et al. 2011). The spore and pollen assemblage reported by Popova et al. (2019b) differs from the one reported here from the Shish locality; Quercus is diverse and moderately abundant in Shish but absent in the Kumyrtas flora (a single grain identified as Quercus and figured in Popova et al. 2019b, belongs to Fagus). Betula and Pterocarya are much less abundant at Shish. Finally, we compared the Shish River site palynoassemblage with three sections belonging to the late Miocene Ishim Formation (Figure 1 (d–f); Kuz’mina et al. 2019). These assemblages are either dominated by spores and non-pollen palynomorphs, or by Pinaceae and Betulaceae; Fagus and Quercus are absent or occur with single pollen grains. In conclusion, there is strong evidence that the Shish River site spore-pollen assemblage corresponds to the late Oligocene (Chattian) ‘Quercus sibirica- Fagus grandifoliiformis-Pinaceae’ palynoassemblage (Kuz’mina and Volkova 2008; Volkova et al. 2016; Figure 3). This age determination would be consistent with evidence from the macro flora of the Shish River site (see above). Palaeobiogeography A number of major palaeobiogeographical patterns emerge from our study of these Southwestern Siberian plant assemblages. The role of Southwestern Siberia and adjacent Kazakhstan appears to have been fourfold: First, it was a stopover for plant lineages migrating from East Asia (and western North America) to Europe. Second, it may have been the point of origin for new species that subsequently migrated to Europe. Third, it had a number of endemic species. Fourth, a few species and lineages might have arrived from the west, where they have older records than in Southwestern Siberia. The first pattern is seen in Nelumbo protospeciosa that existed in Northeast Asia during the Eocene, from where it migrated to Central Asia. Records from the Zaysan depression (Iljinskaya 1986) and western Kazakhstan (Zhilin 1989) suggest it existed there during the middle Eocene to early Miocene (Aquitanian). In Europe and the Mediterranean region, this species appears in the late Oligocene. The earliest records of Liquidambar are from the Eocene of western North America and East Asia (Manchester 1999). Liquidambar europaea was recorded from late Eocene to Aquitanian strata in the Zaysan depression and western Kazakhstan (Iljinskaya 1986; Zhilin 1989). In Europe, this species is known from early Oligocene strata (Walther and Eichler 2010). Similar patterns of westward migrations are found in Eucommia palaeoulmioides (Zhilin 1989; Mai 1995), Ulmus pyramidalis (commonly as U. longifolia; Iljinskaya 1986; Zhilin 1989; Denk and Dillhoff 2005; Walther and Eichler 2010) and in Byttneriophyllum tiliifolium (Central Asian records as Alangium tiliifolium; Knobloch and Kvaček 1964; Zhilin 1989). Ulmus and Byttneriophyllum appear to have restricted stratigraphical ranges in eastern and western Kazakhstan (Aquitanian). A last example of this pattern is found in Quercus kubinyii. Leaf morphologies very similar to this species are known from early Oligocene strata in the Russian Far East (Pavlyutkin 2015) and similar leaf morphologies existed in Aquitanian strata of Central Asia (as Q. kushukensis, Q. cf. castaneifolia; Zhilin 1989). Quercus kubinyii existed in western Eurasia since the Burdigalian (Teodoridis and Kvaček 2006). The second pattern, a likely origin of fossil-taxa in Central Asia with subsequent migration to Europe, is seen in Quercus pseudocastanea (Iljinskaya 1982), and in Pterocarya paradisiaca, Juglans zaisanica, Alnus julianiformis (commonly as Alnus feroniae), Populus balsamoides, and Populus latior, which mainly existed in northern Kazakhstan from the late Oligocene to the Aquitanian with a later arrival in Europe (Kvaček and Holý 1974; Iljinskaya 1986; Zhilin 1989; Walther and Eichler 2010). HISTORICAL BIOLOGY 23 Figure 13. Scanning electron microscopy (SEM) and light microscopy (LM) micrographs of dispersed Fagaceae pollen from the Shish River site. a–c, Fagus subgen. Fagus sp., same grain, (a, c) PV, (b) exine detail. d–g, Quercus subgen. Cerris sect. Cerris, (d, f, g top) same grain, (d, g top) PV, (f) exine detail, (e, g bottom) EV. h–j, Quercus subgen. Quercus sect. Protobalanus, (h, j) EV, (i) exine detail. k–m, Quercus subgen. Quercus sect. Quercus, (k, m) EV, (l) exine detail. SEM (a, b, d, e, f, h, i, k, l), LM (c, g, j, m). PV = polar view; EV = equatorial view. Scale bar 10 μm (a, c, d, e, g, h, j, k, m) and 2 μm (b, f, i, l). 24 T. DENK ET AL. The third pattern, endemic fossil-taxa in the northern Kazakh and Southwestern Siberian records, is represented by Hemitrapa praeconocarpa (Wang 2012), Nyssa sibirica (Zhilin 1989), and potentially by Platycrater iljinskajae, all of which show a stratigraphic range from late Oligocene to early Miocene as well. Finally, a few fossil-taxa in our collection have an older fossil record in Europe than in Kazakhstan and Southwestern Siberia. Among these, Carpinus grandis existed during the early Oligocene in Central Europe (Walther and Eichler 2010), while Quercus section Protobalanus had a highly complex biogeographic history. Today, the golden cup oaks, Quercus sect. Protobalanus comprise a few species in western North America (Denk et al. 2017) but recent palaeobotanical discoveries showed that this geographically restricted group had a much wider distribution during the Cenozoic. Oldest fossils of sect. Protobalanus are known from the middle Eocene of western Greenland (Grímsson et al. 2015). During the latest Eocene and early Oligocene, this group was present in Colorado and New Jersey (Bouchal et al. 2014; Prader et al. 2020) and staminate flowers with in situ pollen from the late Eocene Baltic Amber deposits of Northern Europe (Sadowski et al. 2020) suggest crossing of the North Atlantic during the Paleogene. The finding of Quercus sect. Protobalanus in the Shish River pollen assemblage is the first record of this taxon from Asia and suggests range expansion across the temperate parts of Eurasia during the Paleogene. These time-transgressive migrations suggest that purely biostratigraphic correlations will only work at relatively local geographic scales given plant migration over time. Further, such correlations need to be based upon careful analysis of the taxa involved, including re-investigation of existing published fossil records to detect actual biogeographic patterns (e.g., in the context of the present study, recognising the conspecific nature of Byttneriophullum tiliifolium with ‘Alangium’ tiliifolium and Alnus julianiformis with A. feroniae). In order to fully understand patterns of migration and endemism during different periods and in different parts of northern Eurasia, the palynological and leaf records need to be combined and ‘standard floras’ in the sense of Zhilin (1989) dated by marine molluscs or terrestrial mammals need to be used to achieve reliable stratigraphic frameworks. Acknowledgments We thank the curators of the palaeontological collections at the “Regional Tyumen Museum Complex named after Ivan Slovtsov” for making this collection available and Aleksandra Olokhova for preparing photographs of plant fossil specimens. TD acknowledges financial support through the Swedish Research Council (VR, project no. 2015-03986). This study was funded by the Ministry of Science and Higher education of the Russian Federation and was performed as a part of project FEWZ-2020-0007 “Fundamentals of the natural environment history of the south of Western Siberia and Turgay in the Cenozoic: sequence sedimentology, abiotic geological events and the evolution of the Paleobiosphere“. The investigations were carried out using the equipment of the Center for Collective Use “Bioinert Systems of the Cryosphere”, Tyumen Scientific Center, SB RAS. Valuable comments by Christa Charlotte Hoffman and an anonymous reviewer helped improving the final manuscript. 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