The studied specimens are deposited in the Geoscience Museum at the Georg-August University in Göttingen and bear collection numbers prefixed by GZG.W. (Geowissenschaftliches Zentrum Göttingen, Fossillagerstätte Willershausen), and associated original numbers that were assigned for the publication of specimens in the 1970s and 1980s.
Fossil specimens were photographed with a Sony Alpha 99 II camera equipped with a Tamron SP 90mm macro lens. Line drawings were hand-drawn and hand stroked through transmitted light and enhanced with Photoshop (Adobe Systems software) from the photographs and checked against the specimens. Extant specimens were studied using a binocular microscope Micromed MC-4 Zoom Led and their photographs were taken with a Canon EOS 5D Mark IV Body, Canon MP-E65MM F2.8 Macro lens and Canon Macro Twin Lite MT-26X-RT flash bulb, and stacking was done using Stack-shot 3X with enlarged macro rails s/n 3734; the photosystem is installed on a Kaiser Copy Stand RS 1 reproduction machine. Images were stacked in Helicon Focus 7.7.4 Pro.
The former clay-pit is located in the township Willershausen (51.783724 N, 10.113421 E), ca. 30 km north of Göttingen, Lower Saxony, Germany. From the 16th century to its closure in 1975, the pit exploited clay for nearby brickworks (Ziegelei Schlange). Since 1977 the abandoned pit is a protected Natural Monument (Meischner, 2000), and it was included in the Geopark “Harz, Braunschweiger Land, Ostfalen” in 2012. The Lagerstätte formed in a sinkhole in tectonically disturbed Lower (Buntsandstein) and Middle (Muschelkalk) Triassic sediments above leached late Permian evaporites (Zechstein) (Meischner, 2000). A lake infilling in the sinkhole was 150–200 m in diameter, steep-sided and several tens of meters deep, with a well oxygenated upper water body (epilimnion) and anoxic conditions in lower water column (hypolimnion). Principle lacustrine lithologies comprise a lake margin facies of sand and light-coloured clay with few and poorly preserved fossils (mainly plant detritus, gastropods, bivalves, crayfish exuviae) and a central lake facies of dark clay and carbonates with common and well-preserved fossil content. Almost all of the ~ 50.000 fossils recovered from Willershausen come from a 30 cm thick, laminated bed of lime marl and dolomitic marlstone of the central lake facies (Meischner 2000). Based on the find of Anancus (Mastodon) arvernernsis, Wegele (1914) proposed a Late Pliocene age for the Willershausen biota. Biostratigraphic data from palynomorphs, macroflora and vertebrates (Mohr, 1986; Mai, 1995; Knobloch, 1998) support a Late Pliocene (Piacenzian, 3.6–2.588 Mya) age of the Fossil Lagerstätte Willershausen.
Systematic palaeontology
Family Tenebrionidae Latreille, 1802
Subfamily Tenebrioninae Latreille, 1802
Tribe Helopini Lacordaire, 1859
Subtribe Helopina Lacordaire, 1859
Genus Euboeus Boieldieu, 1865
Euboeus mimonti Boieldieu, 1865
(Figs. 1, 2)
Gersdorf, 1969: 303: Staphylinoidea
Material. One print, sex unknown: GZG.W.16854. Original number: 599–60.
Description of compression print. The body has been strongly deformed during the fossilization, black with reddish inlays at base of head, across pronotum and partly elytra. Only several right antennomeres and right leg without tarsus are partly preserved. Coarse puncturation of round, dense punctures is well visible on the head and the pronotum. The pronotum is partly deformed: the right margin with posterior angle is normal, while the left margin was tucked in when fossilized (Figs. 1c, 2a). The scutellar shield is absent. Left elytron is damaged at the basal third and the apical quarter, whereas the right elytron is partly damaged only at apical portion, but its apex is visible. Widely rounded humeri are well visible. The long striolas are well presented, as well as seven visible elytral striae.
Comments. This specimen was originally assigned to “Staphylinoidea” (Gersdorf, 1969) on the base of supposedly shortened elytra. Gersdorf (1969) assumed that this species may belong to any staphylinid genus with shortened, but still relatively long elytra, for example, Ptomascopus Kraatz, 1876 (Staphylinidae: Silphinae), Velleius Leach, 1819 (Staphylinidae: Staphylininae) or Megarthrus Curtis, 1829 (Staphylinidae: Proteininae). Gersdorf (1969) misinterpreted some structures of this print, especially the not shortened elytra.
Despite the absence of some structures necessary for diagnostics, we can with some confidence attribute this specimen to Euboeus mimonti based on the combination of the following features, which are not characteristic of beetles from other families and other groups of Tenebrionidae: eyes reniform, with ocular cantus; anterior margin of epistoma widely emarginated (Fig. 2, compare with Fig. 2b); lobe-shaped genae, covering the base of the antennae dorsally; moniliform antenna; pronotum and head coarsely punctured by round punctures; pronotum widest at base (Figs. 1c, 2); elytral base much wider than the pronotal one; humeral angles widely rounded, not projected; clear long scutellary striole; at least seven elytral striae well visible as in extant specimens of Euboeus mimonti; walking legs; print length 18 mm (result of fossilization; body length was shorter but not much).
At first glance, this beetle resembles the large European comb-clawed beetle Upinella aterrima (Rosenhauer, 1987) (see images and description in Novák (2015), which has a similar habitus. This impression is especially reinforced by the right side of the pronotum, which is very similar to Upinella: lateral margin evenly rounded, pronotum looks like widest at middle, posterior angles obtuse, not projected. However, we observe a strong deformation of the prothorax during the process of fossilization, because the right side has a different structure: pronotum looks widest at base, posterior angles are projected and acute. The structure of the head refutes the belonging of this fossil species to Upinella Mulsant, 1856 (species of this genus have very large eyes, small genal lobes, short and straight anterior margin of epistoma and very long antennomeres) and fully corresponds to the subfamily Tenebrioninae, especially the small reniform eyes, well-expressed genae and widely emarginated anterior margin of epistoma. In Europe, only Euboeus mimonti has a combination of characters mentioned above, body shape and size (Figs. 1d, e).
Family Tenebrionidae Latreille, 1802
Subfamily Alleculinae Laporte, 1840
Tribe Alleculini Laporte, 1840
Subtribe Gonoderina Seidlitz, 1896
Genus Pseudocistela Crotch, 1874
Pseudocistela aff. cerambioides (Linnaeus, 1758)
(Fig. 3)
Gersdorf, 1969: 323–324, taf. 16, Fig. 9: Alleculidae gen. sp.
Material. 1♂: GZG.W.35146a + b. Original number: 599–22.
Comments. Part and counterpart of this print were well described by Gersdorf (1969), who suggested that the habitus and venation of hindwing of this species are similar to Prionichus Solier, 1835, Hymenalia Mulsant, 1856 and Podonta Solier, 1835. The hind wings are partially folded and cannot be used for diagnostics. Gersdorf (1969, p. 324) indicated that representatives of Podonta have most similar ratios of prothoracic length/prothoracic width, prothoracic length/elytral length and elytral length/width. He placed this species to Alleculinae (originally Alleculidae) as unclear genus. The first co-author supports the opinion of Gersdorf. The specimen has a combination of features usual for Alleculinae and not characteristic of other beetle families in the extant fauna of Europe: size moderate, length 15.8 mm (the beetle was obviously little shorter before fossilization) which makes it possible to exclude small beetles of the superfamily Tenebrionoidea with a similar habitus; large convex eyes; trapezoidal pronotum with weakly rounded lateral margins, strongly narrowed from base to apical margin; basal width of pronotum subequal to elytral base, only slightly narrower; elytra with clear striae consisting of coarse, dense round punctures; well preserved intersegmental membranes between abdominal ventrites 3–5 (Fig. 3c). These membranes are presented only in the tenebrionoid branch of Tenebrionidae (subfamilies Tenebrioninae, Blaptinae, Diaperinae, Stenochiinae and Alleculinae) and indicate the presence of defensive glands, which are widely used in the classification and phylogeny of darkling beetles (e.g., Doyen, 1972; Watt, 1974; Doyen & Lawrence, 1979; Doyen & Tschinkel, 1982; Matthews & Bouchard, 2008; Matthews et al. 2010) as well as in determination of fossil tenebrionids (Nabozhenko, 2019).
We can exclude from the analysis the genus Podonta (tribe Cteniopodini), which has six visible abdominal ventrites and unclear puncturation in striae (small punctures in striae are not different from those in interstriae), because the fossil species has five ventrites and clear large strial punctures. The genera Prionichus, Gonodera Mulsant, 1856 and Pseudocistela are the most similar to the fossil specimen given the size of the body. However, species of Prionichus have a more robust body and a much wider and shorter pronotum, and representatives of the genus Gonodera have the pronotum with obtuse or right posterior angles and unevenly rounded lateral margins. Species of the genus Pseudocistela are the most similar in the combination of the following characters: shape of body, large convex eyes, shape of the pronotum with acute posterior angles and punctures in elytral striae. Species of Pseudocistela have serrate antennomeres, whereas the (partly preserved) antennae of the fossil specimen look filiform. In fact, these filiform remnants are only narrow fragments of antennomeres and cannot be used for generic diagnosis.
The shape of the pronotum of the studied fossil corresponds to that of extant Pseudocistela cerambioides (male), widely distributed in Europe north to the Baltic Sea. Other species from the West Palaearctic have different shapes of the pronotum (Novák 2013).
Family Elateridae Leach, 1815
Subfamily Denticollinae Gistel, 1856
Tribe Selatosomini Schimmel, Tarnawski, Han et Platia, 2015
Genus Selatosomus Stephens, 1830
Selatosomus sp.
(Fig. 4a)
Gersdorf, 1976: 116, taf. 2, Fig. 18a: Tenebrionidae, subfamily Akidinae Solier, 1836
Material. One print, sex unknown: GZG.W.19266. Original number: 52.30143.
Comments. This specimen was determined by Gersdorf (1976) as belonging to the tenebrionid genera Akis Herbst, 1799 or Cyphogenia Solier, 1837 (erroneously written as “Cephogonia” by Gersdorf) (Tenebrionidae: Pimeliinae: Akidini) and accompanied by a photo of Akis bacarozzo (Schrank, 1786) under the name “Cephogonia aurita”. Gersdorf based his identification solely on the shape of the pronotum with depressed lateral sides. In fact, this beetle belongs to the genus Selatosomus (Elateridae), and the edges of the prothorax were depressed during the process of fossilization. The following characters allow to exclude this species from the tribe Akidini: first antennomere is not concealed by gena (almost completely concealed by large genal lobe in Akidini); anterior margin of epistoma short, not emarginated (apical margin wide, widely emarginated in Akidini); eyes round, comparatively large (reniform and dorsally narrow in Akidini); antennomeres short, antennomere 3 short (at least antennomeres 3 and 4 strongly elongate, antennomere 3 longer than antennomeres 4 and 5 together in Akis and Cyphogenia); elytra with clear striae consisting of dense round punctures (without striae and strial puncturation, often without visible elytral puncturation in Akidini).
Family Cerambycidae Latreille, 1802
Subfamily Cerambycinae Latreille, 1802
Tribe Clytini Mulsant, 1839
Genus Xylotrechus Chevrolat, 1860
Xylotrechus sp.
(Figs. 4b, c)
Gersdorf, 1971: 652–653, taf. 62, Fig. 5: Tenebrionidae.
Material. 1♀, part and counterpart: GZG.W.2901a + b. Original number: 599 − 38.
Comments. This species was attributed to the family Tenebrionidae based only on oral opinions of G. Schmidt (expert on Cerambycidae) and H. Korge (expert on Staphylinidae) without any argumentation. The phrase “... but the antennae expressly speak against this, and to a lesser extent the shape of the pronotum” (Gersdorf 1971, p. 653) served as an exception to this species from Cerambycidae. The following characters allow us to exclude this species from Tenebrionidae and assign it to Clytini: antennae are attached to the anterior portion of frons; eyes large and convex, emarginated around the first antennomere attachment point; elytra shorter than abdomen, with rounded apices; intersegmental membranes are absent between 3–5 abdominal ventrites. The pronotum, although somewhat deformed, has the shape and puncturation typical for Clytini. Dr Denis Kasatkin (Rostov-on-Don, Russia), an expert on Cerambycidae, confirmed our opinion and noted that the species similar to the genus Xylotrechus judging by the shape and length of femora, antennae and the last segment of the female abdomen.