Evolutionary Systematics 2 2018, 31–44 | DOI 10.3897/evolsyst.2.22581 Arachnids in Bitterfeld amber: A unique fauna of fossils from the heart of Europe or simply old friends? Jason A. Dunlop1, Ulrich Kotthoff2, Jörg U. Hammel3,4, Jennifer Ahrens5, Danilo Harms5 1 Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, 10115 Berlin, Germany 2 University of Hamburg, Center of Natural History – Geological–Paleontological Museum and Institute for Geology, Bundesstrasse 55, 20146 Hamburg, Germany 3 Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Str. 1, 21502 Geesthacht, Germany 4 Friedrich-Schiller-Universität Jena - Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Erbertstr. 1, 07743 Jena, Germany 5 University of Hamburg, Center of Natural History – Zoological Museum, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany http://zoobank.org/8A229449-E56E-4566-877F-76E75F90667C Corresponding author: Danilo Harms ([email protected]) Abstract Received 28 November 2017 Accepted 16 February 2018 Bitterfeld amber, sometimes referred to as Saxon or Saxonian amber, is a potentially sig- Published 26 March 2018 nificant but poorly known source of arthropod data for the Palaeogene of northern Europe. An important aspect is a long-standing controversy about the age of this amber: namely Academic editor: whether it is equivalent to, and perhaps merely a southerly extension of, the better-known Martin Husemann Baltic amber, or whether it is a unique and geological younger deposit sampling a different fauna. Here, we briefly review the Bitterfeld arachnids with particular emphasis on how Key Words these data could be used to elucidate the age of this deposit. Five arachnid orders have been recorded from Bitterfeld amber: spiders (Araneae), acariform mites (Acariformes), parasit- iform mites (Parasitiformes), harvestmen (Opiliones) and pseudoscorpions (Pseudoscor- Arachnida piones). This is a lower diversity than Baltic amber, where scorpions (Scorpiones) and Fossil camel spiders (Solifugae) have also been recorded. Spiders are the most comprehensively Palaeogene studied group, with more than 75 described species. Other groups such as pseudoscorpions Sachsen-Anhalt and mites appear to be very diverse, but are virtually undescribed. Morphological overlap Faunal comparison is apparent in the arachnid fauna and 40 species are currently shared between Baltic and Bitterfeld amber whilst 50 species are unique to the Bitterfeld deposit. At the family level overlap is even higher, but in all groups Baltic amber appears more diverse than Bitter- feld. This overlap may be interpreted as evidence for temporal conspecifity of the Baltic and Bitterfeld ambers, albeit with the Bitterfeld and Baltic ambers possibly representing independent localities within a larger Eocene European amber area which also included the Rovno amber from the Ukraine. However, caution should be exercised because the tax- onomic foundation for such assumptions is far from comprehensive, most of the material remains to be studied in detail using modern techniques of morphological reconstruction. There are further issues with date estimates because some arachnid groups show extraor- dinary morphological stasis over time, even at species level, which may bias the analyses available. Here, we review the available knowledge on Bitterfeld arachnids and discuss how a detailed assessment of this fauna, and other arthropod taxa, could be generated. Several natural history museums – including Hamburg and Berlin – as well as private collectors host major assemblages of Bitterfeld fossils which may help to clarify the debate about the age and provenance of the material, and the extent to which (morpho)-species were maintained both over geographical distances and potentially geological time. Copyright Jason A. Dunlop et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 32 Jason A. Dunlop et al.: Arachnids in Bitterfeld amber: A unique fauna of fossils... Introduction cast ‘Braunkohle’ mine at Goitsche near Bitterfeld; a historical overview of which can be found in Liehmann Bitterfeld amber originates from near the town of the same (1997). Surveys of the site began in the 1920s with min- name in the eastern state of Sachsen-Anhalt in Germany. ing planned for the 1940s before being interrupted by the It is sometimes referred to as Saxon or Saxonian amber. war. Afterwards, activities resumed and the necessary For general overviews see, e.g., Kosmowska-Ceranow- canal and railway links were put in place. Proper min- icz and Krumbiegel (1989), Krumbiegel (1997), Weits- ing began in the 1950s under the auspices of the GDR chat (1997), Knuth et al. (2002), Wimmer et al. (2009) and utilized three main areas or ‘Baufelder’. During the and Dunlop (2010). The presence of amber in this region 1970s the ‘Volkseigener Betrieb Ostseeschmuck’ of the has been known for a long time, but scientific study of GDR – in other words, the publically owned Baltic sea its inclusions together with their geological setting only jewelry organization – based in Ribnitz-Damgarten had really began with collections made during the time of the difficulties obtaining sufficient raw amber from Russia German Democratic Republic (GDR) (see History). Sev- for their jewelry production. In 1974 the ‘VEB Ostsee- eral groups of plants and arthropods have been recovered schmuck’ were made aware of the presence of amber from Bitterfeld amber (e.g. Weitschat 2008), including deposits at Goitsche, specifically in ‘Baufeld IIIa’, and fossil species shared with the better known Baltic amber by 1975 they had come to an arrangement with the local as well as unique Bitterfeld taxa. Thus, one of the key ‘Braunkohlenkombinat’, or BKK, at Bitterfeld to actively questions about Bitterfeld amber is whether it shares the mine it; see also Führmann (1975) for details. This work same Eocene age as Baltic amber and other ambers, such was initially done by hand, but still yielded more than as Rovno amber from the Ukraine. Indeed, some authors 1000 kg of raw amber in 1975. In successive years the proposed that Bitterfeld is merely a southerly outcrop of process was automatized – the amber being washed out of the wider Baltic amber forest (e.g. Szwedo and Sontag the sediment – resulting in larger yields, such that by the 2013) and refer to Bitterfeld amber as “Tertiary Baltic 1980s between 20,000 up to almost 50,000 kg of amber amber forest incl. the Bitterfeld deposit” (e.g. Wunder- was being recovered per year. lich 2004b). During this time, it also became apparent that, like Alternative hypothesis stressed the uniqueness of Baltic amber, Bitterfeld amber also contained animal and the Bitterfeld deposit, dating its inclusions to a younger plant inclusions. Many specimens were transferred from Oligocene or even Miocene age. Geochemical data now Ribnitz-Damgarten to the Museum für Naturkunde Berlin clearly indicate that Bitterfeld and Baltic amber are not (W. Mey, pers. comm.), and further co-operations with identical (e.g. Wolfe et al. 2016). This debate is not en- the Geiseltal Museum in Halle and the Museum of the tirely trivial as it impacts on questions about how long Earth in Warsaw were undertaken (Krumbiegel 1997). plant and arthropod species, or their wider lineages, could The arthropod inclusions in Berlin were passed onto the survive essentially unchanged in the Cenozoic of north- relevant (zoological) curators for identification, leading to ern Europe and help to evaluate apparent cases of mor- initial reports on the fauna by Barthel and Hetzer (1982) phological stasis in a temporal context. Here, we review and Schumann and Wendt (1989). Early descriptions of these issues with particular focus on our specialist group, individual insect groups included beetles (Hieke and Pi- the arachnids, and draw attention to the presence of pre- etrzeniuk 1984), wasps (Sorg 1986), bugs (Koteja 1986) viously undescribed Bitterfeld material in public and pri- and caddis flies (Mey 1988). Amber mining ceased in vate collections which may help to answer these ques- 1990, around the time of German reunification, and after tions about the composition, age and distribution of the the mine was flooded. The original locality is no longer fauna. We also discuss the state of knowledge concerning accessible, having been deliberately flooded in 1998 as the Bitterfeld fossils and how this fauna could be stud- part of a larger landscape restoration project to form the ied in greater depth to evaluate whether the two ambers ‘Große Goitzschesee’ the north-eastern part of the so- are the same age, but also to improve our understanding called the ‘Bernsteinsee’ or amber lake. Today, several of evolutionary processes of European arthropod faunas museums in Germany hold quite significant collections more generally. of Bitterfeld amber which were purchased or donated by History. Early reports of ‘Saxon’ amber were reviewed private collectors. Hunting for amber pieces in Bitterfeld by Kosmowska-Ceranowicz and Krumbiegel (1989) and was also a hobby for many naturalists over time (Gröhn Krumbiegel (1997) and date back to at least the 17th cen- 2012), thus there are many additional fossils in private tury. Several localities around Halle an der Saale – now collections that are potentially available for study. belonging to the federal states of Saxony or Saxony-An- Geological setting and dating controversy. “Bit- halt – were known to have produced amber, pieces of terfeld amber” originates from Lagerstätten in Eastern which were occasionally referred to as ‘Honigsteine’ Germany, of which the Goitzsche Lagerstätte is the most [honey stones]. Some ended up in the curiosity cabinets important (see above). Stratigraphically, the horizons of the local gentry, and in the late 19th century Saxon am- comprising amber pieces are of Upper Oligocene Age ber was even used for pipe heads or cigarette tips. (Chattian, 23.0–28.1 Ma; Knuth et al. 2002; Blumensten- Most of the current Bitterfeld amber material (see gel 2004) or Lower Miocene according to earlier publi- also Geological Setting) originates from a former open- cations (e.g., Barthel and Hetzer 1982, see below), but evolsyst.pensoft.net Evolutionary Systematics 2 2018, 31–44 33 the age of the amber itself could be significantly older. ed that the Bitterfeld area was positioned at the northern Paleobiologists commonly agree that the arthropod as- coast of the Bohemian High during the Eocene, between semblages in Bitterfeld amber are very similar to those 49 and 48°N, south of the connection between the North in Baltic amber (e.g. Wunderlich 2004a–r; Weitschat and Sea and the Eocene Turan Sea. The region of Rovno was Wichard 2010; Szwedo and Sontag 2013). The term “Bal- also situated at the south of this marine connection, but tic amber” is commonly used for succinite from deposits farther eastwards, and was probably part of the Volhynian around the Gulf of Gdańsk (Fig. 1). This amber probably High (Popov et al. 2004). The region of Gdańsk was sit- originates from Eocene members of the Sciadopityaceae uated at the south coast of the Russian Land, at the other (e.g. Wolfe et al. 2009; Wolfe et al. 2016) or – as also side of the sea arm connecting the North and the Turan discussed for Bitterfeld amber by Yamamoto et al. (2016) Sea, at ~50°N. This sea arm probably closed during the – the Pinaceae (e.g. Mosini and Samperi 1985, Wolfe et Oligocene (e.g. Popov et al. 2004). Wimmer et al. (2009) al. 2016). Possibly, the amber has been reworked and re- discussed the fact that a transport of amber from the deposited in several regions, for example, around Rovno Gdańsk region to the Bitterfeld Lagerstätte is unlikely and (Ukraine; Fig. 1) and, as discussed here, near Bitterfeld proposed that former paleogeographic studies and exam- in Germany (Fig. 1); see also Szwedo and Sontag (2013). inations of inclusions are necessary. While both Baltic and Bitterfeld amber consist of In general, the age of any given amber is notorious- succinite, their chemical signatures differ (Vávra 2008). ly difficult to determine because the amber pieces them- Röschmann (2008) suggested that both amber types de- selves cannot be dated, only the sediments in which they rive from geographically separated forest types, which are found. The option to use sporomorphs, particularly would be in accordance with the early to middle Eocene pollen, to biostratigraphically date amber pieces is ham- palaeogeography (Fig. 1). Similarly, Wolfe et al. (2016) pered since they cannot easily be extracted from amber, suggested, based on detailed geochemical tests, that both which may explain that there are not yet many related Bitterfeld and Baltic amber are of the same Eocene age, studies for both Baltic and Bitterfeld amber. The question but of different source areas. Unfortunately, the latter au- remains: Has older amber become reworked into younger thors seem to show a figure with Miocene paleogeography strata? This is a particular problem at Bitterfeld, such that (Wolfe et al. 2016, fig. 6 therein) to indicate the position of as mentioned above, three alternative ages can be gleaned the forests during the Eocene. Based on other authors (e.g. from the contemporary literature: namely Eocene (e.g. Popov et al. 2004, Denk and Grimm 2009, Wimmer et al. Szwedo and Sontag 2013), Oligocene (e.g. Bartel et al. 2009, and Szwedo and Sontag 2013), it can be conclud- 2015) or Miocene (e.g. Rikkinen and Poinar 2000). In Figure 1. Paleogeographic map of Europe during the early to middle Eocene. Yellow areas indicate the position of the present-day amber Lagerstätten at Bitterfeld, Gdansk and Rovno. Modified after Popov et al. 2004, Denk and Grimm 2009, Blakey 2011, Szwe- do and Sontag 2013, and Wolfe et al. 2016. evolsyst.pensoft.net 34 Jason A. Dunlop et al.: Arachnids in Bitterfeld amber: A unique fauna of fossils... other words, the amber could be as old as 49 Ma or as Table 1. Summary of the forty species of arachnid described young as 20 Ma. A lot can happen in twenty-nine million from both Bitterfeld and Baltic amber. Sequence of families years and the true age of the Bitterfeld inclusions is rele- largely follows the most recent phylogenetic hypotheses. vant to questions such as the palaeoclimate and ecology Taxon Source reference of the original forest environment. Based on published OPILIONES estimates, the amber could have been deposited during a CADDIDAE warm phase not long after the Palaeocene-Eocene Ther- Dunlop and Mitov 1. Caddo dentipalpus (C. L. Koch & Berendt, 1854) mal Maximum (ca. 55 Ma, e.g. Westerhold et al. 2009) (2009) with mean annual temperatures in Central Europe of PHALANGIIDAE ~22 °C (as reconstructed for the Eocene Messel Lager- 2. Dicranopalpus ramiger Dunlop and Mitov stätte by Grein et al. 2011), or at a cooler time during the (C. L. Koch & Berendt, 1854) (2009) Oligocene/Miocene (e.g. Larsson et al. 2010). The dating 3. Lacinius bizleyi Mitov, Dunlop & Penney, 2015 Mitov et al. (2015) controversy can essentially be summarized as pitting evi- SCLEROSOMATIDAE 4. Leiobunum longipes Dunlop and Mitov dence from the geological setting – which tends to support Menge in Koch & Berendt, 1854 (2009) a younger date – against evidence from the fossils which NEMASTOMATIDAE includes numerous examples of species shared with Bal- 5. ?Histricostoma tuberculatum Dunlop and Mitov tic amber. This in turn could imply that the ambers are the (C. L. Koch & Berendt, 1854) (2009) same (Eocene) age, and perhaps even sampled the same PSEUDOSCORPIONES fauna and environment. CHEIRIDIIDAE The earliest works on the inclusions (e.g. Barthel and 6. Cheiridium hartmanni Judson in Weitschat Hetzer 1982) dated Bitterfeld amber to the Miocene, with (Menge in Koch & Berendt, 1854) (2008) an absolute date of ca. 22 Ma. Initial descriptions of both ACARIFORMES plant and animal species generally accepted this Mio- SMARIDIDAE cene date, and it was still being used in the late 1990s 7. Fessonia grabenhorsti Barthel et al., 2015 Bartel et al. (2015) by authors such as Röschmann and Mohrig (1995) and 8. Fessonia wunderlichi Bartel et al., 2015 Bartel et al. (2015) Jähnichen (1998). However, doubts were raised even at ARANEAE the time of the first scientific studies and a brief survey of DIPLURIDAE 9. Clostes priscus Menge, 1869 Wunderlich (2004a) the spiders by Wunderlich (1983) is the first paper we are TELEMIDAE aware of which postulated that Bitterfeld amber is simply 10. ?Telema moritzi Wunderlich, 2004b Wunderlich (2004b) an older (Eocene) resin reworked into younger sediments. SEGESTRIIDAE Several subsequent authors have expressed similar views, 11. Vetsegestria quinquespinosa Wunderlich, 2004b Wunderlich (2004b) see especially Weitschat (1997). All of them large based OONOPIDAE their interpretations on the presence of species common 12. Orchestina (Baltorchestina) brevis to both Baltic and Bitterfeld amber (see also Table 1). Wunderlich (2008a) Wunderlich, 2008a As pointed out by Szwedo and Sontag (2013), if Bit- CYATHOLIPIDAE terfeld and Baltic amber are the same age there is a risk 13. Balticolipus kruemmeri Wunderlich, 2004j Wunderlich (2004j) that authors may have overlooked similar forms in Bal- 14. Succinilipus abditus Wunderlich, 2004j Wunderlich (2004j) tic amber and described Bitterfeld taxa as different and SYNOTAXIDAE new under the assumption that they were considerably 15. Acrometa cristata Petrunkevitch, 1942 Wunderlich (2004k) younger. In this scenario ‘endemic’ Bitterfeld taxa may 16. Succinitaxus brevis Wunderlich, 2004k Wunderlich (2004k) eventually turn out to be synonyms of Baltic species. THERIDIIDAE At the same time, the arguments for conspecific taxa 17. Balticoridion dubium Wunderlich, 2008b Wunderlich (2008b) proving that the ambers are the same age are also un- 18. Episinus balticus Marusik & Penney, 2004 Wunderlich (2008b) 19. Euryopis bitterfeldensis Wunderlich, 2008b Wunderlich (2008b) derlain by an assumption: namely that (morpho)species 20. Euryopis streyi Wunderlich, 2008b Wunderlich (2008b) do not remain static over several million years. Without 21. Hirsutipalpus varipes Wunderlich, 2008b Wunderlich (2008b) independent data on how long, geologically, a partic- 22. Kochiuridion scutatum Wunderlich, 2008b Wunderlich (2008b) ular species can survive there is a risk of both camps 23. Lasaeola infulata (C. L. Koch & Berendt, 1854) Wunderlich (2008b) falling back on circular arguments: identical species 24. Spinitharinus bulbosus Wunderlich, 2008b Wunderlich (2008b) in different ambers indicate deposits of a similar age, 25. Spinitharinus cheliceratus Wunderlich, 2008b Wunderlich (2008b) or identical species in different ambers indicate stable, 26. Succinobertus adjacens Wunderlich, 2008b Wunderlich (2008b) long-lived morphotypes inhabiting the Palaeogene of 27. Ulesanis ovalis Wunderlich, 2008b Wunderlich (2008b) north–central Europe. 28. Ulesanis parva Wunderlich, 2008b Wunderlich (2008b) 29. Unispinatoda aculeata Wunderlich, 2008b Wunderlich (2008b) ANAPIDAE (see notes on Comaromidae in text) Materials and methods 30. Balticoroma ernstorum Wunderlich, 2004h Wunderlich (2004h) 31. Balticoroma gracilipes Wunderlich 2004h Wunderlich (2004h) Raw data on arachnid species numbers were drawn from 32. Balticoroma serafinorum Wunderlich, 2004h Wunderlich (2004h) the summary lists by Dunlop et al. (2017) and Harms and evolsyst.pensoft.net Evolutionary Systematics 2 2018, 31–44 35 Taxon Source reference Results 33. Flagellanapis voigti Wunderlich, 2004h Wunderlich (2004h) 34. Saxonanapis grabenhorsti Wunderlich, 2004h Wunderlich (2004h) Arachnid fossils in Bitterfeld amber are actually not so MYSMENIDAE rare and five of the nine orders that occur naturally in 35. Eomysmenopsis spinipes Wunderlich, 2004h Wunderlich (2004h) Europe today have been recorded: spiders (Araneae), 36. Mysmena groehni Wunderlich, 2004h Wunderlich (2004h) acariform mites (Acariformes), parasitiform mites (Par- ZOROPSIDAE 37. Succiniropsis kutscheri Wunderlich, 2004o Wunderlich (2004o) asitiformes), pseudoscorpions (Pseudoscorpiones), and HAHNIIDAE harvestmen (Opiliones) (Fig. 2). By contrast, scorpions 38. Cymbiohahnia parens Wunderlich, 2004n Wunderlich (2004n) (Scorpiones), palpigrades (Palpigradi), schizomids (Schi- DICTYNIDAE zomida) and camel spiders (Solifugae) are not currently 39. Balticocryphoeca curvitarsis Wunderlich, 2004n Wunderlich (2004n) known from Bitterfeld amber, although both scorpions LIOCRANIDAE and camel spiders are known from Baltic amber (Dun- 40. Apostenus bigibber Wunderlich, 2004q Wunderlich (2004q) lop et al. 2004; Dunlop and Klann 2009; Lourenço 2016). There are particularly significant collections of spiders, Dunlop (2017) together with the relevant primary litera- for which more than 75 fossil species have been de- ture. Specimens used for digital imaging were obtained scribed, most of them in recent years by Jörg Wunderlich from the Palaeontological Collections of the CeNak (Tables 1–2) who referred to an “Eocene Bitterfeld am- Hamburg, the Palaeontology Department of the Zoolog- ber forest” (e.g. Wunderlich 2017, p. 16). This species ical Museum in Berlin, and the Private Collection Gra- number is still negligible compared to the better-known benhorst. Amber fossils were imaged using a BK Plus and longer studied Baltic amber, from which hundreds of Lab System by Dun Inc. with integrated Canon camera, fossil species have been reported (see Discussion). The macrolenses (65 mm and 100 mm) and stacked using harvestmen fauna has been reviewed in some detail, but Zerene Stacker, which is the default software for the BK the mites and pseudoscorpion fossils from Bitterfeld have System. The specimens were immersed in baby oil (Pe- barely been documented. In the sections below, we briefly naten Pflegeöl, Johnson and Johnson GmbH) to improve review individual groups, before discussing similarities the refractive index, and were imaged using Canon EOS and differences compared to other amber faunas in Eu- 5D and Canon MP-E 65 mm lenses, which are integrated rope. In the Discussion we then proceed with remarks on into the BK system. The images were edited in Adobe innovative methods that could lead to a more detailed as- Photoshop CS6. sessment of this fauna. Several previous studies have imaged Baltic amber Harvestmen. The harvestmen fauna in Bitterfeld am- inclusions using computer tomography (µ-CT), includ- ber was described by Dunlop and Mitov (2009). Five ing Henderickx et al. (2006) and Henderickx and Boone species are shared between Baltic and Bitterfeld ambers, (2014) for pseudoscorpions, and Dunlop et al. (2011, whilst three additional species are presently unique to Bit- 2012) for spiders and acariform mites respectively. Oth- terfeld. Again, the age of Bitterfeld amber is critical for er authors have used the more powerful synchrotron ra- an assessment of this fauna because the findings would diation (SR-µCT) to study arachnids in amber, such as indicate evolutionary stasis of species over extraordinary Heetoff et al. (2009) for an oribatid mite in Dominican long time-periods depending on whether Bitterfeld amber amber and Saupe et al. (2012) for spiders from French is of Eocene or Oligocene age. Such an example of sta- and Spanish amber. As part of our review, we also want- sis appeared possible in that one of the Bitterfeld amber ed to explicitly test whether Bitterfeld amber inclusions harvestmen in the eupnoid genus Lacinius (Fig. 2b) was are amenable to imaging using the synchroton, as this initially considered indistinguishable from an extant spe- approach often yields very high quality sets of mor- cies (Dunlop and Mitov 2009), however this same taxon phological characters directly comparable to modern was later found in Baltic amber too and placed in a new species. In this context two Bitterfeld pseudoscorpion (extinct) species based on slight differences compared to fossils were scanned using SR-µCT, conducted at the its living relatives (Mitov et al. 2015). A mite harvestmen beamline P05 of the storage ring PETRA III (Deutsches belonging to the suborder Cyphophthalami has also been Elektronen-Synchrotron — DESY, Hamburg, Germany) recorded from the genus Siro (Fig. 2a), which occurs to- operated by Helmholtz-Zentrum Geesthacht (Haibel et day in North America and Europe (Dunlop and Giribet al. 2010; Greving et al. 2014; Wilde et al. 2016). Am- 2003). Another Siro species is known from Baltic amber ber pieces were mounted on a beamline standard sam- (Dunlop and Mitov 2011). Some of the recovered har- ple-stubs with plasticine and imaged using attenuation vestmen are interesting from a biogeographic perspec- contrast (Greving et al. 2014). The photon energy ap- tive. The distinctive, large-eyed Caddo does not occur in plied was 25 keV. A total of 1200 radiographic projec- Europe today, with extant species restricted to the Amer- tions were recorded at equal steps between 0 and π. The icas, Japan, and former Gondwanan landmasses such as tomographic reconstruction algorithm “gridrec” was Australia. Cyphophthalmids also do not occur in northern used to yield 32-bit floating point image stacks with iso- Europe nowadays and seem to prefer warmer climates in tropic voxel size of 2.42 µm. southern Europe. evolsyst.pensoft.net 36 Jason A. Dunlop et al.: Arachnids in Bitterfeld amber: A unique fauna of fossils... Figure 2. Examples of arachnids preserved in Bitterfeld amber. A) harvestman Siro platypedibus (Museum für Naturkunde Berlin Coll, No. MB.A. 1086); B) ?Lacinius erinaceus (Museum für Naturkunde Berlin Coll. No. MB.A. 1661); C) undescribed mite species (CeNak Coll. No. BIBS00265); D) a second undescribed mite species (CeNak Coll. No. BIBS00244); E) undescribed pseudoscorpion in the family Chthoniidae (Grabenhorst Coll. No. PS-6); F) first record of the family Pseudogarypidae in Bitterfeld amber (Grabenhorst Coll. No. PS-17); G) undescribed crab spider in the family Thomisidae (CeNak Coll. No.BIBS0433); H) a second undescribed crab spider in the family Thomisidae (CeNak Coll. No. BIBS0481). evolsyst.pensoft.net Evolutionary Systematics 2 2018, 31–44 37 Table 2. The fifty arachnid species so far restricted only to Bit- Taxon Source reference terfeld amber. † indicates an extinct family; sequence of fami- LINYPHIIDAE lies phylogenetic as above. 34. Custodela acutula Wunderlich, 2004m Wunderlich (2004m) Taxon Source reference 35. Custodela bispina Wunderlich, 2004m Wunderlich (2004m) OPILIONES 36. Custodela bispinosa Wunderlich, 2004m Wunderlich (2004m) SIRONIDAE 37. Custodela curvata Wunderlich, 2004m Wunderlich (2004m) Dunlop and Giribet 38. Custodela femurspinosa Wunderlich, 2004m Wunderlich (2004m) 1. Siro platypedibus Dunlop & Giribet, 2003 (2003) 39. ?Custodela parva Wunderlich, 2004m Wunderlich (2004m) PHALANGIIDAE 40. Custodela stridulans Wunderlich, 2004m Wunderlich (2004m) Dunlop and Mitov 2. Amilenus deltshevi Dunlop & Mitov, 2009 41. Custodelela hamata Wunderlich, 2004m Wunderlich (2004m) (2009) NEMASTOMATIDAE 42. Paralabulla bitterfeldensis Wunderlich, 2004m Wunderlich (2004m) Dunlop and Mitov TETRAGNATHIDAE 3. ?Mitostoma gruberi Dunlop & Mitov, 2009 (2009) 43. Anameta distenda Wunderlich, 2004e Wunderlich (2004e) ARANEAE ARANEIDAE PHOLCIDAE 44. Eonephila bitterfeldensis Wunderlich, 2004f Wunderlich (2004f) 4. Paraspermophora bitterfeldensis Wunderlich, Wunderlich (2004b) 45. Eustaloides bitterfeldensis (Wunderlich, 2004e) Wunderlich (2004e) 2004b DICTYNIDAE SEGESTRIIDAE 46. Eocryphoeca bitterfeldensis Wunderlich, 2004n Wunderlich (2004n) 5. Ariadna defuncta Wunderlich, 2004b Wunderlich (2004b) 47. Mastigusa bitterfeldensis Wunderlich, 2004n Wunderlich (2004n) LEPTONETIDAE 6. Eoleptoneta curvata Wunderlich, 2004b Wunderlich (2004b) 48. Mastigusa magnibulbus Wunderlich, 2004n Wunderlich (2004n) 7. Eoleptoneta kutscheri Wunderlich, 1991 Wunderlich (1991) EPHALMATORIDAE† OONOPIDAE 49. Ephalmator bitterfeldensis Wunderlich, 2004o Wunderlich (2004p) 8. Orchestina (Baltorchestina) angulata Wunderlich, Wunderlich (2011, SALTICIDAE 2012 2012) 50. Almolinus bitterfeldensis Wunderlich, 2004r Wunderlich (2004r) 9. Orchestina (Baltorchestina) bitterfeldensis Wunderlich (2008a) Wunderlich, 2008a 10. ?Stenoonops rugosus Wunderlich, 2004b Wunderlich (2004b) In detail (see also Table 1) five species of harvestman ARCHAEIDAE (Opiliones) are found in both ambers. These consist of 11. ?Archaea bitterfeldensis Wunderlich, 2004c Wunderlich (2004c) one species each from the eupnoid genera Caddo (Cad- 12. Saxonarchaea dentata Wunderlich, 2004c Wunderlich (2004c) didae), Dicranopalpus and Lacinius (both Phalangiidae) 13. Saxonarchaea diabolica Wunderlich, 2004c Wunderlich (2004c) and Leiobunum (Sclerosomatidae), and one from the dys- SPATIATORIDAE† pnoid genus Histricostoma (Nemastomatidae) (Dunlop 14. Spatiator bitterfeldensis Wunderlich, 2017 Wunderlich (2017) and Mitov 2009; Mitov et al. 2015). Unique Bitterfeld ULOBORIDAE elements (Table 2) comprise one cyphophthlamid in the 15. Hyptiomopes bitterfeldensis Wunderlich, 2004d Wunderlich (2004d) genus Siro (Sironidae), one eupnoid in Amilenus (Pha- CYATHOLIPIDAE langiidae) and one dyspnoid in Mitostoma (Nemastomati- 16. Spinilipus bispinosus Wunderlich, 2004f Wunderlich (2004f) 17. Spinilipus curvatus Wunderlich, 2004f Wunderlich (2004f) dae) (Dunlop and Giribet 2003; Dunlop and Mitov 2009). 18. Succinilipus aspinosus Wunderlich, 2004f Wunderlich (2004f) Pseudoscorpions. Pseudoscorpions in Bitterfeld am- 19. Succinilipus saxoniensis Wunderlich, 1993 Wunderlich (1993) ber are likely to represent a diverse fauna which, to date, 20. Succinilipus similis Wunderlich, 2004f Wunderlich (2004f) remains largely undocumented. The fossil history of pseu- SYNOTAXIDAE doscorpions was recently reviewed by Harms and Dunlop 21. Chelicerinus abnormis Wunderlich, 2008a Wunderlich (2008a) (2017) and a total of 49 fossil species in 16 families are 22. Cornuanandrus bifurcatus Wunderlich, 2004k Wunderlich (2004k) currently recognised, of which the majority (34 species 23. Cornuanandrus bitterfeldensis Wunderlich, 2004k Wunderlich (2004k) in 12 families) were described from Baltic amber. Our 24. Eosynotaxus bitterfeldensis Wunderlich, 2004k Wunderlich (2004k) preliminary assessment of the Bitterfeld pseudoscorpions NESTICIDAE suggests that at least nine families are present: Chthoni- 25. Eopopino rudloffi Wunderlich, 2004l Wunderlich (2004l) idae, Tridenchthoniidae, Pseudogarypidae, Neobisiidae, THERIDIIDAE Geogarypidae, Cheiridiidae, Chernetidae, Cheliferidae, 26. Lasaeola bitterfeldensis Wunderlich, 2008b Wunderlich (2008b) and Withiiidae. No specimens of Lechytiidae, Feaellidae 27. ?Lasaeola sigillata Wunderlich, 2008b Wunderlich (2008b) and Garypinidae have been observed at Bitterfeld so far, THERIDIOSOMATIDAE although these families do occur in Baltic amber. In con- 28. Eotheridiosoma tuber Wunderlich, 2004g Wunderlich (2004g) trast to Baltic amber where bark-dwelling taxa are clear- 29. Eotheridiosoma volutum Wunderlich, 2004g Wunderlich (2004g) ly dominant, there seems to be an even representation of 30. Spinitheridiosoma bispinosum Wunderlich, 2004g Wunderlich (2004g) ground-dwelling (e.g. Chthoniidae, Geogarypidae) and ANAPIDAE 31. Balticonopsis bitterfeldensis Wunderlich, 2004h Wunderlich (2004h) bark taxa (e.g. Chernetidae, Cheliferidae) by numbers. 32. Balticonopsis ludwigi Wunderlich, 2017 Wunderlich (2017) The families Chthoniidae, Cheiridiidae and Geogarypi- PROTHERIDIIDAE† dae are represented by many fossils at Bitterfeld, and at 33. Protheridion bitterfeldensis Wunderlich, 2004i Wunderlich (2004i) least the chthoniid fauna seems to be diverse which is evolsyst.pensoft.net 38 Jason A. Dunlop et al.: Arachnids in Bitterfeld amber: A unique fauna of fossils... interesting given that only two fossil species have been the described fossil species. Such work is currently being described from Baltic amber (Fig. 2e). undertaken. Also preserved in amber are some key fossils We note that no pseudoscorpion species have yet been that highlight aspects of paleoecology and biology, such formally described from Bitterfeld amber and it is not as prey-interactions and breeding behaviour (Fig. 3b), known whether the samples in various collections rep- that provide insights into paleoenvironments and the ani- resent new species, species that are already known from mals that lived in those environments. Baltic and/or Rovno amber, or a mix of both. A shared Bal- Mites. The mite fauna preserved in Bitterfeld amber tic/Bitterfeld pseudoscorpion (Pseudoscorpiones) Chei- appears diverse, both at the generic and species level, and ridium hartmanni (Cheiridiidae) was listed by Weitschat for both of the mite groups that are currently suggested (2008), although we have not been able to confirm the by molecular analyses (Parasitiformes and Acariformes). source of this record of an established Baltic species in Two species of smaridid mites in the parasitengonid genus Bitterfeld amber from the primary literature and it ap- Fessonia have been described (Table 1) which also occur pears to be a pers. comm. from Mark Judson. Geogaryp- in Baltic amber (Bartel et al. 2015). Fossils potentially be- idae are known from Baltic amber with three species one longing to Mesostigmata (Parasitiformes) and Oribatida of which, Geogarypus garskii, has also been described (Acariformes) have also been observed, but not formally from Rovno amber but not Bitterfeld amber. Some of described (Dunlop 2010). Fragments of Labidostoma- the Bitterfeld pseudoscorpions are currently identified tidae in the prostigmate mite fauna (Acariformes) have as Baltic amber species in the collections but these iden- been noted, but again not formally described (Sidorchuk tifications rely on historical descriptions that are often and Bertrand, 2013). The probably basal parasitiform poor and these samples could just as well represent dis- mite taxon Opilioacariformes has been described from tinct species pending detailed taxonomic analyses. As the Baltic amber (Dunlop et al. 2004) but no specimens are preservation of many Bitterfeld samples does not allow known yet from Bitterfeld. The same is true for ticks as for a detailed study (e.g. the amber is too dark to see the the most commonly known group in the Parasitiformes: trichobothria, or artefacts are present), new methods need rare Baltic records, but none from Bitterfeld. No further to be applied for detailed studies, such as Synchotron mi- data are currently available and we have to conclude that crotomography (e.g. Henderickx et al. 2012; Henderickx both Acariformes and Parasitiformes are likely to repre- and Boone 2016). Such studies are particularly valuable sent a diverse, but currently unexplored, fauna. In lieu of for putative new species, such as many of the smaller ch- formal descriptions, the implications of the mite data for thoniids (Fig. 4a), but also those that are interesting in a questions of dating and biogeography remain open. wider perspective, such as the Pseudogarypidae (Figs 2f, Spiders. As noted above, the vast majority of the fossil 4b). This family is reported here for the first time from arachnids in Bitterfeld amber are spiders (e.g. Fig. 2g, h). Bitterfeld amber and occurs today only in North America More than 75 species in 26 families have been described, and Tasmania (Harvey 2013), although fossils are com- almost exclusively by Jörg Wunderlich across several mon in Baltic amber from which five species have been papers and monographs (Wunderlich 1983, 1991, 1993, described. One of these species, Pseudogarypus minor, 2004a–r, 2008a–b, 2012, 2017). Published records include has also been reported from Rovno amber, but methods members of three extinct spider families recorded from other than conventional light microscopy need to be ap- Bitterfeld material, although the status of these families – plied to check if the Bitterfeld sample belongs to any of Spatiatoridae†, Protheridiidae† and Ephalmatoridae† – has Figure 3. Examples of behavioral traits preserved in Bitterfeld amber: A) complete spider exuvia of an unidentified species (CeNak Coll. No. BIBS0514); and B) evidence of a lithobiomorph centipede preying on a pseudoscorpion (Grabenhorst Coll. No. My-1). evolsyst.pensoft.net Evolutionary Systematics 2 2018, 31–44 39 not been tested using cladistic methods. The mygalomorph (Cyatholipidae) (Wunderlich 2004j). These families spider fauna at Bitterfeld is currently poor (Wunderlich occur today only in disjunctive distributions across the 2004a), with only one species shared with Baltic amber. Southern Hemisphere but are diverse in Bitterfeld (and It belongs to the curtain-web spiders (Dipluridae) which Baltic) ambers with numerous species. Others, such as are absent in Europe today, but speciose across several the Leptonetidae and Telemidae (Wunderlich 1991, continents in the southern hemisphere. There is a diverse 2004b), do not occur in north–central Europe today but leaf-litter fauna comprising oonopids, hahniids, anap- are still present in southern Europe, up into France, and in ids, mysmenids and zoropsids (e.g. Wunderlich 2004h, Asia. These taxa may have suffered range retraction since 2008a, 2017). Since amber is fossilised tree resin, typical the Neogene, contracting to known fauna refugia such as elements of the ‘bark’ fauna are present such as Segest- the Balkans and the Iberian Peninsula (e.g. Schmitt and riidae (Wunderlich 2004b), but the diversity of the web Varga 2012). Although probably the best documented of building spiders is certainly highest, with several species the Bitterfeld arachnids at species level, the spider fau- of linyphiids (Wunderlich 2004m) and theridiids (Wun- na is also the most problematic for a number of reasons. derlich 2008b), plus further species in the Tetragnathidae First, there has been no attempt to discriminate Baltic and (Wunderlich 2004e) and Uloboridae (Wunderlich 2004d). Bitterfeld ambers in the past and both faunas have gen- True orb-weavers (Araneidae) seem comparatively rare erally been treated in unison by taxonomists, implying a (Wunderlich 2004e–f). Wolf spiders (Lycosidae), crab spi- priori that they are identical. Second, the descriptions of ders (Thomisidae) and nursery web spiders (Pisauridae) many of the fossil spiders are problematic. Historical re- are absent; all groups that are diverse in European eco- cords from Baltic amber may be very brief and unreliably systems today. Their absence may be due to their typical illustrated. In other cases higher taxa were raised without lifestyles, which are not associated with trees. A high pro- a strong underlying phylogenetic analysis. For exam- portion of species seems to be shared with Baltic amber ple, the three extinct families noted above are current- (Table 1) although it needs to be emphasised that a crit- ly diagnosed (Wunderlich 2004i, p) on characters such ical morphological assessment for many of the described as clypeal and leg ratios, or patterns of spination, which Bitterfeld species is lacking, and that the descriptions for are not clearly expressed as apomorphies. An evaluation many species are insufficient to test for conspecifity. In of Bitterfeld spider faunas compared to those present in some groups, species are not shared at all, such as in the Baltic or Rovno amber cannot be undertaken at species linyphiids and theridiosomatid with species unique to Bit- level at this stage pending detailed revisions, and we need terfeld amber (Wunderlich 2004g, m) (see also Table 2) to fall back to the family level where identifications are or vice versa. The relationships of many species to Rovno relatively reliable. Here, the faunas certainly overlap and amber fossils are also uncertain. many families and genera are shared (Table 1). Some of the described spiders are of considerable In detail, thirty-two spider species have been described biogeographical interest such as the pelican spiders (Ar- from both Baltic and Bitterfeld amber. Among the myga- chaeidae) (Wunderlich 2004c) and cyatholipid spiders lomorph spiders there is one common species in the ge- Figure 4. The Bitterfeld amber pseudoscorpions shown in Figs 2E–F imaged this time using synchrotron-based microtomography; these are the first Bitterfeld arachnid fossils to be examined using this technique. A) Chthoniidae (Grabenhorst Coll. No. PS-6); B) Pseudogarypidae (Grabenhorst Coll. No. PS-17). In the PDF click on the image to access an interactive 3D model. evolsyst.pensoft.net 40 Jason A. Dunlop et al.: Arachnids in Bitterfeld amber: A unique fauna of fossils... nus Clostes (Dipluridae). For Synspermiata there is one ator (Mantophasmatodea), two termites (Isoptera), three shared species in Telema (Telemidae), one in Vetsegestria bugs (Heteroptera), twenty-three thrips (Thysanoptera), (Segestriidae) and one Orchestina (Onopidae). Among seven barklice (Psocoptera), eight scale insects (Cocci- entelegyne spiders, there is one common Balticolipus and na), nine aphids (Aphidina), one scorpionfly (Mecoptera), one Succinilipus (both Cyatholipidae), one Acrometa and three lacewings (Neuroptera), eleven hymenopterans one Succinitaxus (both Synotaxidae). There is one Balti- (Hymenoptera), and fifty-one flies and midges (Diptera). coridion, one Episinus, two Euryopis, one Hirsutipalpus, Since Weitschat’s publication, other authors have com- one Kochiuridion, one Lasaeola, two Spinitharinus, one mented on the insect fauna in particular to argue that the Succinobertus, two Ulesanis, and one Unispinatoda (all two ambers contain the same fauna. For example, Szwe- Theridiidae). There is one shared Flagellanapis and one do and Sontag (2013) reviewed the biting midges (Cer- Saxonanapis, three Balticoroma (all Anapidae; although atopogonidae) from the three European amber deposits Wunderlich recognised a family Comaromidae including and found them highly similar although the Bitterfeld Balticoroma), and one Eomysmenopsis and one Mysme- fauna was less diverse, however their study was founded na (both Mysmenidae). In the derived ‘RTA clade’ group on the assumption that “…there is no doubt that amber there is one Succiniropsis (Zoropsidae), one Cymbio- from Bitterfeld is contemporaneous with Baltic amber…” hahnia (Hahniidae), one Balticocryphoeca (Dictynidae), which may have biased the interpretation. Wichard (2013) and one Apostenus (Liocranidae). studied aquatic insects and found “wide-reaching simi- By contrast the forty-seven unique endemic spiders larities” between the amber faunas, but also exercised taxa (Table 2) include for Synspermiata one Parasper- caution because most of the Bitterfeld taxa are currently mophora (Pholcidae), one Ariadna (Segestriidae) and undescribed and need to be studied in detail. two Orchestina and one Stenoonops (both Oonopidae). Unfortunately, there are no comprehensive published For entelygyne spiders the following taxa are reported: summaries of the number of endemic Bitterfeld insect two species in the genus Eoleptoneta (Leptonetidae), one species for comparison, but in contrast to the similarities Archaea and two species in the Bitterfeld endemic ge- observed by some authors, Alekseev and Grzymala (2015) nus Saxonarchaea (Archaeidae), one species in the genus described nine tenebrionid beetles from Baltic and Bitter- Spatiator of the extinct family Spatiatoridae, one species feld amber but did not find any shared species between in the Bitterfeld endemic genus Hyptiomopes (Ulobori- both deposits. Bukejs et al. (2016) provided a checklist of dae), two Spinilipus and three Succinilipus (both Cyatho- beetle species described from Bitterfeld amber and found lipidae), one Chelicerinus, two Cornuanandrus and one some species to be shared, although other species (and Eosynotaxus (all Synotaxidae), one Eopopino (Nestici- genera) are unique to Bitterfeld (Lyubarsky and Perovsky dae), two Lasaeola (Theridiidae), one Eotheridiosoma 2017). In summary, most palaeoentomological studies and one Spinitheridiosoma (both Theridiosomatidae), suggested at strong similarities between Baltic and Bitter- two Balticonopsis (Anapidae), one Protheridion (the ex- feld ambers, but also noted that taxonomic knowledge is tinct family Protheridiidae), seven Custodela, one in the still very fragmentary. Since there are limited data about Bitterfeld endemic Custodelela and one Paralabulla (all how long species can stay morphologically unchanged in Linyphiidae), one Anameta (Tetragnathidae), one Eone- the insect fauna, this still does not provide more than an phila and one Eustaloides (both Araneidae). For the RTA indication that both ambers are of the same age. clade there is one Eocryphoeca and two Mastigusa (both Geographical distinctness. The most comprehensive Dictynidae), one Ephalmator (the extinct family Ephal- study assessing geochemical data was presented by Wolfe matoridae) and one Almolinus (Salticidae). Additional et al. (2016). These authors found differences in the geo- taxonomic information may be derived from a diverse chemical properties and argued that both ambers may be spectrum of partially or entirely preserved exuvia that overlapping in time, but may represent paleolatitudinal dif- could be identified to family level (Fig. 3a). ferences with sources originating from the northern (Baltic) and southern (Bitterfeld) margins of the Paleogene North Sea. If this is true, the arthropod fauna of both ambers may Discussion be seen as a mix of widely distributed taxa on several land- masses in the Paleogene of Europe that were bisected by In the last comprehensive survey of the faunal overlap substantial bodies of water, but perhaps also of more nar- between the two ambers, Weitschat (2008) listed a grand rowly distributed taxa that were found at lower latitudes total of 167 species (plants and arthropods) shared be- than their Baltic amber relatives. The Bitterfeld fauna is tween the Baltic – in his table “Samland” – and Bitterfeld still of significance then because it represents a snapshot of deposits. For plants these consisted of eight liverworts, arthropod diversity with unique fossils that perhaps thrived seven mosses and one flowering plant. He also document- under slightly warmer climates and perhaps a different veg- ed twenty-six shared species of spiders (Araneae), one etation. In any case, a detailed and comprehensive study is pseudoscorpion (Pseudoscorpiones) and two millipedes necessary to evaluate and compare these hypotheses. (Diplopoda); his list is in strong contrast to the revised The arachnid data from Bitterfeld amber certainly sup- arachnid data of forty-two species above. For insects, he ports the insect data as Bitterfeld amber appears to have listed three common stick insects (Phasmida), one gladi- a lower arthropod diversity compared to Baltic amber, al- evolsyst.pensoft.net