PalZ DOI 10.1007/s12542-017-0367-3
RESEARCH PAPER
First record of insects in lignite-bearing formations (upper Eocene) of the central German Leipzig Embayment Lutz Kunzmann1 • Christian Mu¨ller1 • Karolin Moraweck1,2 • Dorothea Bra¨utigam1 Torsten Wappler3,4 • Andre´ Nel5
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Received: 7 December 2016 / Accepted: 27 May 2017 Ó Pala¨ontologische Gesellschaft 2017
Abstract The first unequivocal insect remains from compression plant assemblages of the central German Leipzig Embayment (former Weißelster Basin) are reported and briefly described. The fossil taphocoenosis comes from the upper Bartonian or lower Priabonian Luckenau Clay complex (lignite-bearing Borna Formation) that represents sediments of coastal alluvial braidplain origin. Autecological interpretations of insect taxa are in accordance with plant-based environmental reconstructions as three of five insect taxa are closely related to freshwater environments. Based on the accompanying plant assemblage the palaeoclimate of the habitat is characterized as ‘‘subtropical’’ and humid, but with a distinctive seasonality in precipitation. Keywords Fossil aquatic insects Palaeoecology Palaeoclimate Fossil leaf assemblage Zeitz floristic complex
Kurzfassung Die ersten eindeutigen Insektenreste aus fossilen Pflanzenvergesellschaftungen in Inkohlungserhaltung aus der mitteldeutschen Leipziger Bucht (fru¨her Weißelster-Becken) werden bekannt gemacht und in knapper Form beschrieben. Die fossile Taphozo¨nose entstammt dem Luckenau-Tonkomplex der braunkohlefu¨hrenden Borna-Formation (oberes Bartonium oder unteres Priabonium), welcher a¨stuarine und alluviale Sedimente beinhaltet. Eine auto¨kologische Interpretation der Insekten-Taxa steht im Kontext zu den pflanzenfossilbasierten Rekonstruktionen. Drei der fu¨nf Insektentaxa sind Anzeiger von Su¨ßwasserhabitaten. Auf der Grundlage der assoziierten Pflanzenvergesellschaftung kann das Pala¨oklima des Habitats als ‘subtropisch’ und humid mit einer ausgepra¨gten Saisonalita¨t der Niederschla¨ge charakterisiert werden. Schlu¨sselwo¨rter Fossile aquatische Insekten Pala¨oo¨kologie Pala¨oklima Fossile Blattflora Florenkomplex Zeitz
Handling editor: Mike Reich. & Lutz Kunzmann
[email protected] 1
Senckenberg Natural History Collections Dresden, Ko¨nigsbru¨cker Landstr. 159, 01109 Dresden, Germany
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Technical University Dresden, Institut of Botany, Zellescher Weg 20b, 01217 Dresden, Germany
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Hessisches Landesmuseum Darmstadt, Friedensplatz 1, 64283 Darmstadt, Germany
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Rheinische Friedrich-Wilhelms-Universita¨t Bonn, Steinmann-Institut fu¨r Geologie, Pala¨ontologie und Mineralogie, Nussallee 8, 53115 Bonn, Germany
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Institut de Syste´matique, E´volution, Biodiversite´, ISYEBUMR 7205-CNRS, MNHN, UPMC, EPHE, Muse´um National d’Histoire Naturelle, Sorbonne Universite´s, 57 rue Cuvier, CP 50, Entomologie, 75005 Paris, France
Introduction The obvious absence of vertebrate and invertebrate fossils is a remarkable character of non-consolidated siliciclastic lignite-bearing successions in the Cenozoic of central Europe. Any mineralized tissue of animals was dissolved under the influence of migrating humic acids originating from organic material such as peat. Neither casts nor moulds of former fossils could be preserved in non-consolidated gravels, sands, silts, and clays. Rare evidence of animal life is indicated by trace fossils (e.g. Standke et al. 2010), biomarkers in sediments (e.g. Otto et al. 2002), and leaf damage caused by arthropods (e.g., Wappler 2010; Wappler et al. 2012; Wappler and Grı´msson 2016).
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In contrast, a rich and diverse animal life in former peatlands is indicated by numerous faunal elements in fully marine horizons that are intercalated in the same sections, or in exceptional formations of lignites within deposits of non-consolidated siliciclastics. The latter is known from special parts of Geiseltal lignites (middle Eocene; SachsenAnhalt, Germany) where, under the influence of carbonaceous fluids originating from Triassic beds, complete skeletons of horses etc. are preserved (Krumbiegel et al. 1983). The former is the case for instance in the early Oligocene Bo¨hlen Formation, central Germany, in which Rupelian sediments contain parts of sea cows, crocodiles, sharks, bivalves, etc. (Mu¨ller 2008). The underlying, predominantly estuarine, fluvial, and brackish Gro¨bers Member and the overlying, predominantly fluvial and estuarine Thierbach Member of the Cottbus Formation again lack any hard parts of former animal life. Careful observations of thousands of specimens with fossil plant remains from respective lignite-bearing formations of non-consolidated sediments in the central German Leipzig Embayment (formerly mentioned as Weißelster Basin, see e.g. Standke et al. (2010) for terminology) confirm the general statement (Walther and Kunzmann 2008). Moreover, insect remains that partly consist of organic chitin which usually withstands diagenetic and other processes should be present in respective taphocoenoses, but have also not been recognized yet. Surprisingly, investigations of more than 2300 sediment slabs with several thousands of fossil leaves and carpological remains from the ‘‘classic’’ Luckenau Clay complex (Kunzmann et al. 2016) revealed the first unequivocal insect remains from respective horizons. Herein we give a short report on and descriptions of these findings with preliminary ecological indications which are in accordance with the interpretation of the depositional facies and the fossil plant assemblage. For better characterization of the environment palaeoclimate parameters were calculated from the leaf assemblage using the CLAMP approach (Spicer 2009).
Materials and methods The fossil material was collected in September 1999 in the Profen opencast mine of the Mibrag mbH mining company (Sachsen-Anhalt, central Germany; Fig. 1). More precisely, the site was situated within the nowadays abundant Su¨d excavation field (site UTM coordinates: 33U 56.68875 N, 30.12500 E; 108–110 m asl). The plantbearing horizon (Fig. 2) is part of the underlying layer of the main lignite seam complex of the Cenozoic Leipzig
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Embayment corresponding to the uppermost part of the Zeitz Member of the Borna Formation (regional lithostratigraphy; Standke et al. 2010; Fig. 3). The sediments of the sampling horizon represent a coastal alluvial braidplain and are usually called the Luckenau Clay complex (LC). Although the LC lithostratigraphically belongs to the Zeitz Member, it is not sufficiently resolved whether it should be placed into the regional Spore-Pollen-Paleogene (SPP) zone 17/18 or into zone 18 (Krutzsch 2011; Fig. 3). The latter would imply an affiliation to the overlaying Bruckdorf Member (Standke et al. 2010). Furthermore, according to Krutzsch (2011), SPP zone 17/18 is considered to be latest Bartonian whereas zone 18 is placed into the early to middle Priabonian. Following its lithostratigraphic position this flora belongs to the ‘‘late’’ Eocene floristic complex Zeitz (Mai and Walther 1985, 2000; Kunzmann et al. 2016), which was erected in particular from floras of the Zeitz Member, but also expands to the floras of the Bruckdorf Member. The Zeitz floristic complex is characterized by Mai and Walther (2000) as broad-leaved notophyllous vegetation consisting of ca. 65% evergreen, ‘‘subtropical’’ to warm-temperate elements. By phytosociological means, Kvacˇek (2010) proposed the term broad-leaved evergreen riparian gallery forest, with palms for this type of azonal vegetation of the Leipzig Embayment. The Profen-Su¨d-LC phytotaphocoenosis is currently under taxonomic investigation; preliminary, but meaningful results are used to characterize the palaeovegetation (Kunzmann et al. 2016). Even though very rich in Steinhauera (Altingiaceae) and Rhodomyrtophyllum (Myrtaceae), and thus a typical riparian community, the Profen-Su¨d-LC flora lacks common elements of the Zeitz complex assemblages such as Eotrigonobalanus (Fagaceae), conifers and the diversity in Lauraceae and Theaceae. By contrast, cf. Manglietia (Magnoliaceae), aff. Berberis (Berberidaceae), Sloanea (Elaeocarpaceae), and Vaccinioides (Ericaceae) are frequent, and several species that are previously unknown from the Zeitz floristic complex occur, amongst which there is a remarkable variety of dentate leaf forms (Kunzmann et al. 2016). In its composition that differs from those of most of the previously known Zeitz complex assemblages, this flora gives rise to a number of phytosociological and developmental questions which will be content of further studies. Furthermore, a quantitative analysis of insect damage types on the leaf component of the flora was conducted (Mu¨ller 2016). Insect remains are found on finely laminated light to dark brownish-gray silty-clayey sediments with leaf compressions (Fig. 4). Specimens are stored in the palaeobotanical collection of the Senckenberg Natural History
First record of insects in Eocene strata of the central German Leipzig Embayment Fig. 1 Location of the fossil site in the Profen opencast mine (red-bordered area), SachsenAnhalt, Germany. Asterisk indicates the position of the sampling site within the former Su¨d excavation field; for coordinates and further information see text
Collections Dresden (acronym MMG PB). They were examined and digitized using a Keyence VHX-1000 microscope, and all relevant structures were measured from the digitized images. All photographs were optimized using Adobe Photoshop CS6 and Adobe Lightroom CC. We follow the wing venation nomenclature of Kukalova´-Peck (1991) for the Trichoptera. Terminologies used for external features in the Hymenoptera primarily follow those established by Bohart and Menk (1976). Limited knowledge of the taxonomic composition of the flora hampers the application of the Coexistence Approach (CA; Mosbrugger and Utescher 1997; Mosbrugger et al. 2005) for estimation of palaeoclimatic parameters. However, about 2500 specimens providing more than 4000 individual leaf remains are accessible for the Climate Leaf Analysis Multivariate Program (CLAMP) approach. CLAMP is a multidimensional tool correlating certain leaf physiognomic characters with climatic parameters, which was first introduced by Wolfe (1993) and further developed by various authors (e.g. Spicer 2009; Teodoridis et al. 2011; Yang et al. 2011; Khan et al. 2014; Ding et al. 2017). The physiognomic characters of fossil leaves from woody angiosperms are correlated with those of extant plant assemblages and their climatic requirements using meteorological data by Canonical Correspondence Analysis (CCA) (Spicer 2009; Teodoridis et al. 2011; Yang et al. 2011). The analysis was performed online using the online analysis option of the CLAMP approach (http://www.clamp.ibcas.ac.cn). The respective calibration dataset was determined following Teodoridis et al. (2012). The estimation is based on the Physg3brcAZ leaf physiognomic dataset and the GRIDMet3brAZ dataset using global gridded meteorological data. For a detailed methodological description see also Moraweck et al. (2015).
Systematic palaeontology Phylum Arthropoda Siebold, 1848 Class Insecta Linnaeus, 1758 Order Trichoptera Kirby, 1815 ? Family Polycentropodidae Ulmer, 1903 Genus and species incertae sedis Figure 5a Studied material. MMG PB Pf 1344; very fragmented wing base; length 7.88 mm, width approx. 2.77 mm. Description. Two wing bases, showing bases of all main veins; no visible cross vein between C and ScP; separation of R into RA and RP 2.33 mm from wing base, at the same level as separation between M and CuA; M appearing as a rather weak vein; CuA strong and dark; an oblique cross vein between RP and M 1.88 mm from base of RP; an oblique cross vein between M and CuA 1.33 mm distally; a strong oblique cross vein between CuA and CuP 0.85 mm distal from separation of M and CuA, thus the part of CuA between two points very long; CuP simple and weaker than CuA; a strong oblique long cross vein between AA and CuP 0.35 mm distal of apex of anal loop; anal veins form a double anal loop, first one between AA and AP1 ? 2, with a cross vein in its basal half; second one between AP1 ? 2 and AP3 ? 4 broader but distinctly shorter. Remarks. Among the modern families of Trichoptera, few have a very long portion of CuA between its separation from M and first cross vein between CuA and CuP; points of separations between RA and RP and between M and CuA at the same level; and a double anal loop, i.e., the Polycentropodidae and the Hydropsychidae:
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First record of insects in Eocene strata of the central German Leipzig Embayment b Fig. 2 Outcrop with sampling horizon: high wall with basalmost
measure of the main lignite seam complex (L) and underbedding Luckenau Clay complex (S—sampling horizon), Z—fluvial, estuarine, and brackish-marine sandy complex of the Zeitz Member (image taken September 1999), Profen opencast mine, Su¨d excavation field. Please note, for occupational safety and health standards the high wall was not walkable; fossiliferous sediment blocks were removed by an excavator
Arctopsychinae (Malicky 2004). The Arctopsychinae have no strong cross vein in the first anal loop (Schmid 1968; Stocks 2011), unlike our fossil and some Polycentropodidae. Among the Polycentropodidae (Ola´h and Johanson 2010), the following modern genera have the cross vein between CuP and CuA at the basal part of the first anal loop, instead of being well distal of it: Neucentropus Martynov, 1907 (Li et al. 1998), Neureclipsis McLachlan, 1864, Plectrocnemia Stephens, 1836, Holocentropus McLachlan, 1864, Cyrnus Stephens, 1836, Polycentropus Curtis, 1835, Nyctiophylax Brauer, 1865, Cyrnopsis Martynov, 1935, Cyrnellus Banks, 1913, Cyrnodes Ulmer,
Fig. 3 General lithostratigraphic section of Paleogene sediments in the Leipzig Embayment, central Germany, showing the position of the sampling horizon within the Zeitz Member. Horizons, members
1910, Cernotina Ross, 1938, Pahamunaya Schmid, 1958 (Ulmer 1910; Martynov 1935; Ross 1938; Neboiss 1993). In Polyplectropus Ulmer, 1905 and Adectophylax Neboiss, 1982, the portion of CuA between its separation from M and first cross vein between CuA and CuP is distinctly shorter than in our fossil, even if the cross vein between CuP and CuA is in a relatively distal position as in our fossil (Neboiss 1982; Chamorro-Locayo and Holzenthal 2010). Our fossil would possibly require the establishment of a new genus and species, but it is too incomplete to allow us to be completely accurate of its family position and affinities. Therefore, we prefer to consider it as a possible Polycentropodidae genus and species incertae sedis. Stratigraphic and geographic distribution. Profen opencast mine, excavation field Su¨d, Sachsen-Anhalt, Germany; Luckenau Clay complex, Zeitz Mb., Borna Fm.; late middle to early late Eocene; for stratigraphy and age see Standke et al. (2010) and Krutzsch (2011).
and formations are correlated to global chronostratigraphy according to Standke et al. (2010) and Krutzsch (2011); phytostratigraphic framework is placed accordingly
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Fig. 4 Typical sediment slab with numerous leaf remains from the Luckenau Clay complex, Zeitz Member, Borna Formation, opencast mine Profen-Su¨d, MMG PB Pf 1379
Order Hemiptera Linnaeus, 1758 Suborder Heteroptera Latreille, 1810 Family Aphelocheiridae Fieber, 1851 ? Genus Aphelocheirus Westwood, 1833 ?Aphelocheirus sp. indet. Figure 5b–d Studied material. MMG PB Pf 1345; isolated abdomen in ventral view.
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Description. Abdomen rounded, visible in ventral view, total length 6.0 mm, width 5.5 mm; only the abdominal segments 2–6 are preserved, with a small fragment of the segment 7; each of these segments shows a pair of broad dark and rounded structures, 326.2 ± 19.1 lm wide (N = 6), plus on segment 2, a pair of supplementary elliptical structures appressed to them and nearer to lateral margins of segment; each segment bears a short but distinct lateral spine.
First record of insects in Eocene strata of the central German Leipzig Embayment
Remarks. The rounded shape of the abdomen and the shape of the segments exactly correspond to those of an aquatic Heteroptera taxon of the Naucoridae, as well as of the Aphelocheiridae. The lateral spines of the segments are present in the Aphelocheiridae, rather than in the Naucoridae. A more decisive argument for an attribution to the Aphelocheiridae is the presence of the broad rounded structures visible in ventral view that exactly correspond to the broad abdominal respiratory ‘‘rosettes’’ characteristic of this family (Thorpe and Crisp 1947; Schuh and Slater 1995). The elliptical structures appressed to the rosettes of the 2nd abdominal segment correspond to the sense organ that is present in this position in extant bugs. Therefore, this fossil, despite its incompleteness, can be attributed to the aquatic family Aphelocheiridae, and probably to the sole extant genus Aphelocheirus. The Aphelocheiridae are quite rare in the fossil record. Nel and Paicheler (1992) indicated that the Early Cretaceous genus Canteronecta Mazzoni, 1985 (originally considered as a Notonectidae) belongs to the Naucoridae or to the Aphelocheiridae. The shape of the rounded abdomen with strong lateral spines on each segment rather suggests an attribution to the latter family, but without any certainty (Mazzoni 1985). Popov (2007) regards the bug genera Atoposita Jordan, 1967 and Coreoidus Jordan, 1967 (Pliocene of Germany) to be synonymous with Aphelocheirus (Jordan 1967; Popov 2007). The Palearctic genus Aphelocheirus accommodates 98 extant species (Xie and Liu 2014) and is rarely known from the fossil record. From the accessible literature a single fossil-species is reported, A. affinis (Popov 2007). Stratigraphic and geographic distribution. Profen opencast mine, excavation field Su¨d, Sachsen-Anhalt, Germany; Luckenau Clay complex, Zeitz Mb., Borna Fm.; late middle to early late Eocene; for stratigraphy and age see Standke et al. (2010) and Krutzsch (2011). Order Hymenoptera Linnaeus, 1758 Superfamily Apoidea Latreille, 1802 or Vespoidea Latreille, 1802 Genus and species undetermined Figure 5e Studied material. MMG PB Pf 1346; fragmented, proximal part of an isolated forewing. Description. A forewing fragment, 7.5 mm long, 2.75 mm wide; wing surface light brown except for the costal cell that is dark brown; costal cell well defined, 0.27 mm wide; vein M distinctly curved and aligned with basal part of vein Rs; cell 1 M broad and elongate with apical part acute;
vein 1cu-a slightly distal of base of M; cell 1R1 as broad as cell 1 M; no anal vein. Remarks. The absence of any anal vein excludes affinities with the symphytan families. Within the Apocrita, this type of cells 1R1 and 1 M can be found in the Apoidea sensu Debevec et al. (2012), e.g., in some Nyssonidae (or Sphecidae: Nyssoninae) in which 1cu-a is distal to the base of M forming hexagonal cell 1 M (Gorytes, Clitemnestra, etc.). Some Vespoidea (Pompilidae) don’t have this type of cells 1R1 and 1 M, but they have a curved vein M as in our fossil (Bohart and Menk 1976; Finnamore and Michener 1993). A more precise attribution is not possible. Stratigraphic and geographic distribution. Profen opencast mine, excavation field Su¨d, Sachsen-Anhalt, Germany; Luckenau Clay complex, Zeitz Mb., Borna Fm.; late middle to early late Eocene; for stratigraphy and age see Standke et al. (2010) and Krutzsch (2011). Order Coleoptera Linnaeus, 1758 Genus and species undetermined Figure 5f Studied material. MMG PB Pf 1359; large isolated elytron; ventral view. Description. A large isolated elytron, 14.25 mm long, 5.5 mm wide; surface smooth, without apparent trace of striation; lateral margin broad. Remarks. Based on the presence of only a single isolated elytron and the presence of clearly distinguishable synapomorphic characters, the family placement of this fossil remains unclear. Nevertheless, as for its shape, surface without striation, and large size, this elytron resembles that of an aquatic hydrophilid beetle of the hydrophiline tribe (Hydrophilus type) (Short 2010). Beetles other than hydrophilids have smooth elytra (e.g., Dytiscidae: Graphoderus zonatus has smooth elytra and is essentially the same size as specimen 1359 (Karlsson Green et al. 2013). Of course, it is not possible to be absolutely sure of this attribution, but this fossil would correspond to a third aquatic insect taxon in this small assemblage. Hydrophilids are rather frequent in the fossil record, especially in the Cenozoic (Fika´cˇek et al. 2010). The lacustrine sediments of the Bois d’Asson outcrop (Oligocene, Lube´ron, France) have yielded several similar isolated elytra attributable to hydrophilids (pers. observation A. Nel). Stratigraphic and geographic distribution. Profen opencast mine, excavation field Su¨d, Sachsen-Anhalt, Germany;
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First record of insects in Eocene strata of the central German Leipzig Embayment b Fig. 5 Insect remains from the lignite-bearing formations (late
Eocene) of the central German Weißelster Basin. a fragmented wing remains of caddisfly (Trichoptera) (MMG PB Pf 1344); b isolated hemipteran abdomen (MMG PB Pf 1345), white arrows indicate position of broad dark and rounded structures on the 3rd to 6th abdominal segment, enlarged in c, black arrow indicate position of elliptical structure on 2nd abdominal segment near to the lateral margin, enlarged in d; e nearly complete wing of a vespoid or apoid wasp (MMG PB Pf 1346). Abbreviation for cell and vein names: Cu cubital, M medial, R radial, Rs radial sector, crossveins indicated by lowercase letter, cell names in square brackets; f isolated elytron of an aquatic beetle (MMG PB Pf 1359); g isolated elytron (MMG PB Pf 1351) covered with small setae, enlarged in h; i. isolated elytron (MMG PB Pf 1353). Scale bars represent 1 mm
Luckenau Clay complex, Zeitz Mb., Borna Fm.; late middle to early late Eocene; for stratigraphy and age see Standke et al. (2010) and Krutzsch (2011). Family undetermined Figure 5g–i Studied material. MMG PB 308:1a; fragmented, isolated elytron, ventral view. MMG PB Pf 1351; fragmented, isolated elytron, ventral view. MMG PB Pf 1353, nearly complete preserved elytron, ventral view. Description. Three isolated elytra, light to dark brown. Specimen Pf 1353 is relatively large, 6.75 mm long, 3.75 mm wide; elongate, parallel-sided, apparently rather smooth (Fig. 2i). Specimen Pf 1351 is not completely preserved, about 8.6 mm long; elongate, parallel-sided, with small setae (Fig. 2h), but without any visible striation. Specimen Pf 308:1a is a 9 mm long fragment (complete length would be appr. 10 mm), with small setae as well. Remarks. It is clearly not possible to accurately attribute these fossils to a precise beetle family. Nevertheless, the general habitus of elytron Pf 1353 resembles that of some longhorn beetles (Cerambycidae: Prioninae). Although the three specimens differ in their dimensions they probably belong to the same taxon as they show a similar colour pattern, with a prominent central dark stripe, and are densely covered with setae. Adult Cerambycidae feed on leaves, meristematic cambial tissue or pollen, and their larvae generally mine the phloem of trees or bore into hardwood (Hanks 1999). The oldest record of Cerambycidae (Prioninae) is known from the Early Cretaceous of China (Wang et al. 2014). Stratigraphic and geographic distribution. Profen opencast mine, excavation field Su¨d, Sachsen-Anhalt, Germany; Luckenau Clay complex, Zeitz Mb., Borna Fm.; late middle to early late Eocene; for stratigraphy and age see Standke et al. (2010) and Krutzsch (2011).
Palaeoecological and palaeoclimatic aspects Autecology of the insects Interestingly, two, most likely three of these five insect taxa (Trichoptera: Polycentropodidae, Hemiptera: Aphelocheiridae, Coleoptera: Hydrophilidae or Dytiscidae) are closely related to aquatic environments, with their larvae (or even adult and larvae) living in freshwater. In particular, polycentropodid larvae occur in lotic and lentic habitats, including running waters, swamps, pools, and lakes. They are found on the sides and lower surfaces of large rocks. The Aphelocheiridae prefer the oxygen-rich water of rivers, streams, and brooks, where they walk on the bottom. Their plastron respiration enables them to extract oxygen directly from the water and remain submerged during all their life. If the third taxon is indeed an aquatic hydrophilid beetle it is obviously bound to freshwater habitats. Despite from taphonomic bias that could randomly lead to a preferential selection and preservation of aquatic taxa, this situation is surprising when we compare it to other entomofaunas of similar age. In palaeolakes of the late Eocene of Monteils, and of the Oligocene of Ce´reste and Bois d’Asson in the South of France aquatic insect fossils are extremely rare making up less than 1–2% of the recorded entomofauna. It suggests for the Profen-Su¨d-LC entomofauna that there were freshwater biotas very close to the place of fossilization, in which the quality of water was sufficient for the existence of a certain diversity of aquatic insects. For instance, larvae of Trichoptera exclusively live in freshwater and the biological conditions are strongly influenced by water chemistry and habitat quality. Particularly, alkalinity and dissolved oxygen are highly correlated with aquatic insect assemblages (Rosenberg and Resh 1993). Adults of benthic water bugs (Aphelocheiridae, Hemiptera), water beetles (Dytiscidae), and water scavenger beetles (Hydrophilidae, (Coleoptera) partly show modified antennae for respiration when submerged in water. In addition, the Profen-Su¨d-LC flora reveals a high diversity of well-preserved exophytic and endophytic insect damage, which can be used to analyze the trophic structure within the surrounding riparian forest (Mu¨ller 2016). Phytosociological implications The predominance of Steinhauera (Altingiaceae) and Rhodomyrtophyllum (Myrtaceae) in the taphocoenosis clearly refers to the former presence of a typical central European middle to late Eocene riparian gallery forest community (Kunzmann et al. 2016). Preliminary investigations of leaf taxa revealed submersed water plants such
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as Stratiotes sp. (Hydrocharitaceae) and aff. Zingiberoideophyllum sp. (Zingiberales) (unpublished data). All in all, these observations clearly imply that the plant litter was buried in a freshwater body without water current such as abandoned river channels. Respective fossil assemblages are partly parauthochthonous (e.g. Kunzmann et al. 2016) which means that they represent local vegetation to a high percentage. Palaeoclimatic signal from the plant assemblage Based on 28 morphological leaf types recognized in the Profen-Su¨d-LC flora the palaeoclimate is estimated by using CLAMP as follows: Mean annual temperature: 16.1 °C ± 2.1. Warmest month mean temperature: 23.9 °C ± 2.5. Coldest month mean temperature: 9.1 °C ± 3.4. Growing season precipitation: 1634 ± 317 mm. Precipitation three wettest months: 940 ± 229 mm. Precipitation three driest months: 135 ± 59 mm. These CLAMP data are quite reasonable and are in accordance with a number of other estimates from assemblages of that region and time slice gathered using either CLAMP, CA or phytosociological analyses (see Mai and Walther 2000; Moraweck et al. 2015; Teodoridis and Kvacˇek 2015). Thus, the diverse and exceptionally wellpreserved Profen-Su¨d-LC flora reveals palaeoclimatic results which underpin the assumptions of Mai and Walther (1985, 2000), who characterized the late Eocene climate in central Germany as ‘‘subtropical’’ and humid with a recognizable seasonality in the distribution of precipitation. Moraweck et al. (2015) reconstructed MAT and MAP for the Zeitz floristic complex using CA and CLAMP. MAT between 16.9–18.0 °C and MAP between 1308–1335 mm are calculated by CA, whereas CLAMP suggests slightly warmer temperatures, i.e. MAT 20.0 ± 1.3 °C (Moraweck et al. 2015). It is worth considering that recently the pCO2 content of the palaeoatmosphere was calculated from leaf cuticles of the Luckenau Clay complex using the stomata ratio method (e.g. Steinthorsdottir et al. 2016). Steinthorsdottir et al. (2016) determined a pCO2 value ranging from 397.33 ± 68.7 ppm to 678.12 ± 117.25 (average 537.73 ± 92.98 ppm) derived from SD data from the extinct Eotrigonobalanus furcinervis (Fagaceae). Compared to estimates from the marine record (Zachos et al. 2001, 2008; Zhang et al. 2015) Steinthorsdottir et al. (2016) calculated lower absolute values for pCO2, but this pattern is known from and valid for nearly all stomatabased pCO2 reconstructions. However, these reconstructions display the same trend from higher pCO2 values in the late Eocene towards decreasing pCO2 values in the Eocene–
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Oligocene transition (Steinthorsdottir et al. 2016), and thus they can be used as valid proxies.
Conclusions After more than 150 years of palaeontological sampling and investigations in the middle to upper Eocene formations of the Leipzig Embayment (former Weißelster Basin) in central Germany, the first unequivocal insect remains are recognized from a diverse plant taphocoenosis at the Profen-Su¨d opencast mine. Fossil insect remains are briefly described and accommodated in five taxa. This record opens new opportunities for a more detailed characterization of these coastal habitats and the ecosystem structure on an alluvial braidplain to estuarine marshland. Fossil insect remains are rare, but meaningful and their occurrence fit into the habitat model which predicts a floodplain with rivers, abandoned channels and lakes acting as traps in which biota parts were fossilized. The existence of local freshwater environments is also indicated by the plant taphocoenoses which contains submersed water plants as well as litter from a riparian gallery forest. Two, most likely three of these five insect taxa populate freshwater environments. Proxy data refer to a ‘‘subtropical’’ climate with seasonality in precipitation and a still high level of atmospheric pCO2 at about 5 Ma prior to the Eocene–Oligocene boundary. Acknowledgements The authors thank the Mibrag mbH company Zeitz (Sachsen-Anhalt, Germany) for giving the permit to do field work and sampling in the Profen-Su¨d opencast mine as well as for the maps and geological sections provided, in particular we thank former chief geologist Thomas Fischkandl for his kind support. During sampling and processing of the samples, the authors were supported by the staff members of the palaeobotanical section of Senckenberg Dresden Carola Kunzmann and Denise Hennig. We are also grateful to Jo¨rg Ansorge (Greifswald), an anonymous reviewer and the editorin-chief (Mike Reich) for their helpful comments on the manuscript.
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