Quasicalathus conservans Schmidt & Will, sp. nov., fossil species from the Eocene Rovno amber, herein designated.

Three fossil species from Eocene amber deposits of Central Europe:

Quasicalathus agonicollis Schmidt & Will, sp. nov. (Baltic amber).

Quasicalathus conservans Schmidt & Will, sp. nov. (Rovno amber).

Quasicalathus elpis (Ortuño & Arillo, 2009), new combination (Baltic amber).

Taxon with characteristics of Calathina and Calathus, respectively, as defined by Lindroth (1956) and Ball and Nègre (1972). The combination of the following character states defines the group:

Head: normal for Calathina, not thickened (Figs 24, 41, 81); mandibles normal for Calathina, not broadened, not elongated (Figs 2, 52); eye size averaged for Calathina, normally protruded (Figs 24, 41); antennae pubescent from fourth antennomere (Fig. 20); mentum tooth simple or slightly truncated at tip, with two fine setae near its base (Figs 52, 82); submentum with two setae each side in normal position, with the internal setae robust and the external setae markedly short and thin (Figs 31, 52, 84).

Prothorax: pronotal shape subquadrate (“calathoid” form; Figs 3, 14, 34, 42, 50, 58–60, 63, 64, 73, 78), slightly or moderately constricted toward base, with lateral margin straight or slightly concave before base, and with basolateral angles slightly or moderately obtuse (Figs 9, 14, 25, 42, 50, 63, 64, 74, 78); basolateral angles not protruded posteriorly; basal margin beaded laterally (level of basolateral angles); basolateral seta situated at margin (Figs 9, 14, 20, 25, 42, 50, 66, 74); pronotal disc with sculpticells of microsculpture transverse, very narrow (magnification 80×). Prosternum impunctate, smooth, prosternal process with or without apical bead (Figs 37, 38, 51, 75, 85).

Pterothorax: elytra slender, ovate, glabrous, humeral tooth absent; basal bead moderately or markedly concave with humeral angle +/- markedly protruded anteriorly (Figs 9, 14, 25, 34, 47, 58–61, 66, 74, 78); epipleuron without plica (Fig. 53); striae slightly to moderately deeply engraved, with punctures evident (Figs 25, 27, 58); intervals flat to moderately convex; parascutellar seta present (Figs 14, 66, 74); third interval with a single rather short, thin discal seta situated near the end of the apical elytral 2/3, adjoining second stria (Figs 11, 12, 16, 27, 29; but see comments to the redescription of Q. elpis, below), with surroundings of setigerous puncture not depressed; external intervals without setae; intervals with sculpticells of microsculpture transverse, very narrow, narrower than on pronotum (Fig. 26; magnification 100×, elytra appearing polished at 40×). Metepisternum elongate (Figs 4, 62, 83). Hindwings fully developed.

Legs: length average for Calathina, neither markedly slender nor particular robust (Figs 4, 7, 30, 36, 49, 62); male protarsomeres dilated; mesocoxa with a single ridge seta; metacoxa trisetose, with anterior seta large and with the two posterior setae small and thin, one located near external, one near internal margin (Figs 54, 67, 86; but see comments to the redescription of Q. elpis below); metatrochanter with seta present (but see comments to the redescription of Q. elpis, below); metafemur with two setae on ventral surface, and with dorsoapical setae present; metatibia in male not densely pubescent; tarsi without pubescence or wrinkles on dorsal surface; meso- and metatarsomeres I–IV without external and internal lateral grooves; fifth tarsomeres with a single pair of dorsal setae, and with two pairs of ventral setae; claws pectinate (Fig. 8).

Abdomen: ventrites smooth aside from normal setation; apical ventrite in both sexes with one pair of seta near apical margin (Fig. 53).

Female genitalia (Figs 55–57, 76, 77): basal gonocoxite about two times longer than apical gonocoxite; apical gonocoxite short, sickle-shaped, with one ensiform seta at dorsal and two ensiform setae at external margin, and with sensory pit large, well-developed, with two setae; basal gonocoxite without setae near apical margin; bursa copulatrix not markedly sclerotized.

Male genitalia (Figs 43–46, 68–72, 80, 87–89): aedeagus right side ventral in repose; right paramere styloid with distal portion very long and slender, not terminated in a distinct apical hook; left paramere ovoid; median lobe with long apical lamella, without apical disc.

The name of the new subgenus is derived from the Latin conjunction “quasi” (like; as it were) and the name of the ground beetle genus Calathus, and thus refers to the morphological similarity to representatives of this genus.

Presence of a styloid right paramere (an apomorphic character state within Sphodrini) differentiates Quasicalathus gen. nov. from Atranopsina and Synuchina. Additionally, Quasicalathus lacks the stridulation organ that is an autapomorphy for Atranopsina (Casale 1988). Presence of well-developed sensory pit of the apical gonocoxite (plesiomorphic state) differentiates Quasicalathus from Synuchina (Casale 1988) and Dolichina sensu Sciaky and Facchini (1997), Sciaky and Wrase (1998) and Hovorka (2017b). Aedeagus with right side ventral in repose (right paramere styloid, left paramere ovoid; plesiomorphic state) differentiates Quasicalathus from Pristosiina. The combination of the following characters states places Quasicalathus outside of Sphodrina sensu Casale (1988): Mentum tooth not bifid (plesiomorphic state); antennae pubescent from fourth antennomere (plesiomorphic state); tarsomeres without pubescence and smooth on dorsal surfaces (plesiomorphic state); claws pectinate (symplesiomorph with Sphodrini except Atranopsina, reversed in some Sphodrina); aedeagal median lobe slender with long terminal lamella. The shape of the aedeagal median lobe and its terminal lamella is rather variable within Calathina, Dolichina and Synuchina (Lindroth 1956, Habu 1978, Casale 1988).

Based on the overall similarity in external and genitalic characters the new, fossil genus Quasicalathus strongly resembles extant species of subtribe Calathina and genus Calathus (see next section). However, as it was comprehensively discussed by Schmidt and Will (2020), monophyly of Calathina is supported by molecular data (Ruiz et al. 2009, 2010) while Calathus seems to be paraphyletic, and morphological data supporting Calathina monophyly are currently unknown. As a consequence, the definite, evidence-based, placement of fossil Quasicalathus species in this subtribe is currently impossible. What can be stated regarding the systematic placement of this taxon is the following:

1. Quasicalathus is included in the “P clade” of Ruiz et al. (2009) based on the shared presence of the markedly styloid right paramere, which is most likely an autapomorphy of this clade. Atranopsina and all but one outgroup, Zabrini, are characterized by much shorter parameres. The styloid right paramere shows a pattern of homoplasy across carabids and is considered a separate transformation in Zabrini as this group has not been shown to be the sister group to Sphodrini in relevant phylogenetic analyses (Ruiz et al. 2009, Gomez et al. 2016).
2. Quasicalathus is not a member of Synuchina, Dolichina or Pristosiina, as each of these sphodrine subtribes is characterized by respective autapomorphic states that are not present in the fossil specimens.
3. Quasicalathus is not a member of Sphodrina sensu Casale (1988) because each of the genera affiliated to this subtribe is characterized by at least one autapomorphic state that is not present in Quasicalathus (see above).
4. Given the lack of apparent morphological synapomorphies for subtribe Calathina and the genus Calathus there is currently no evidence that places Quasicalathus within, or as sister of, any one of these clades.

Fossils are basic for understanding the evolutionary history of species groups and fossil specimens are critical for time calibration of phylogenetic hypotheses. Therefore, in order to prevent misleading interpretations–e.g., the incorrect assignment of fossils that lack evidence of their placement–we propose the systematic position of Quasicalathus using a conservative, synapomorphy-based approach. This requires establishing the genus without a certain position within the sphodrine “P clade” of Ruiz et al. (2009), i.e., Sphodrini, informal group P clade, incertae sedis.

The overall similarity of Quasicalathus gen. n. with species of the genus Calathus makes it necessary to provide a detailed differential diagnosis of the new genus. Recently, Schmidt and Will (2020) presented an overview to the diagnostic characters of the currently accepted genera and subgenera placed within Calathina, and respectively Calathus, sensu Hovorka (2017a). The Eocene Quasicalathus differs from all calathine species groups by presence of a single elytral discal seta (but see Remarks section to the redescription of Calathus elpis, below). All but one Calathina are characterized by presence of at least two elytral discal setae, while the elytra of Tachalus Ball & Nègre lacks discal setae. Quasicalathus additionally differs from all calathine taxa, with the exception of Bedelinus Ragusa, by having a simple mentum tooth (entire instead of bifid), and trisetose metacoxa. Quasicalathus differs from all but the Himalayan Spinocalathus Schmidt by narrow transverse sculpticells of elytral microsculpture (nearly isodiametric in other Calathina). A slightly transverse pattern of elytral microsculpture is developed in some species of Denticalathus Schmidt, however, species of this group differ by pubescent third antennomere in addition to other characters mentioned above and below. Bedelinus and Spinocalathus differ from Quasicalathus additionally by removal of the pronotal laterobasal pronotal seta from the lateral margin, plus presence of lateral grooves on metatarsomeres I–IV. Quasicalathus differs from Spinocalathus by the short metepisterneum, and from Bedelinus and most Spinocalathus by presence of an apical hook on the right paramere. Quasicalathus shares meso- and metatarsomeres I–IV without external and internal lateral grooves with Iberocalathus Toribio, Lindrothius Kurnakov, some species of Calathus s. str., Denticalathus, and Neocalathus Ball & Nègre. However, species of these groups differ by presence of an apical hook on the aedeagal right paramere (Lindrothius, Calathus s. str., Denticalathus, Neocalathus) and by a markedly sclerotized spermatheca plus presence of a single ensiform seta along the external margin of the apical gonocoxite (Iberocalathus).

Here we hypothesize that i) presence of a single elytral discal seta and ii) presence of narrow transverse sculpticells of elytral microsculpture are synapomorphies of Quasicalathus gen. n.; the similarly developed pattern of elytral microsculpture in Spinocalathus and some Denticalathus are hypothesized as homoplasious as these groups share more derived patterns in some morphological features (e.g., bifid mentum tooth, bisetose metacoxa) together with other Calathina groups.

Not studied; see Material and methods, above.

The original description of the fossil species C. elpis is doubtful or confusing with respect to some important diagnostic characters, these are:

1. Elytra near middle with two setiferous pores in the 5 ^th interval. This pattern of chaetotaxy was not found in any of the fossil species we investigated. In contrast to what was presented by Ortuño and Arillo (2009), we believe that discal setae are absent in the 5 ^th interval of the C. elpis holotype specimen. It seems likely that the observation of the authors is based on a misinterpretation of micro-structures on the elytral surface of the fossil that are preservation artifacts and thus produce a false impression of existing setiferous pores. This interpretation is supported by the following three facts:
2. First, in the reconstruction drawing of the holotype specimen, Ortuño and Arillo (2009: 57, fig. 1d) figured a seta corresponding to each of the reconstructed setiferous pores in the 3 ^rd interval (these pores were found in all fossils we studied by us) but do not show those of the external intervals. Therefore, we believe that the authors may have observed structures in the external intervals that appear similar to (but not identical with) setiferous pores but do not bear setae.
3. Second, Ortuño and Arillo (2009: 57, fig. 1d) figured pore-like structures in the 6 ^th elytral intervals close to the 5 ^th striae but not in the 5 ^th interval (as reported in their description). Such setation pattern is unknown in sphodrine beetles, fossil or extant. Presence of setiferous pores in the 6 ^th elytral interval would also represent a markedly anomalous setation pattern, last but not least because the path of the cubital-1 nerve follows the 5 ^th elytral interval (Jeannel 1926).
4. Third, the character combination ‘3 ^rd interval uni-setose + one of the external intervals pluri-setose’ is absent in all other fossil and extant sphodrine species and therefore it is also very likely absent in C. elpis.
5. Ortuño and Arillo (2009: 58, fig. 2d) presented a reconstruction drawing of the C. elpis metacoxa that is bisetose in an irregular way: adjacent to the anterior seta an additional seta on the interior side of the posterior metacoxal surface was figured. Because this setation pattern is unknown in all Sphodrini and other Harpalinae, we believe that it is based on an erroneous interpretation of the actual coxal chaetotaxy of C. elpis. Although the majority of sphodrine species are characterized by bisetose metacoxae with one anterior and one posterior seta present, the posterior seta is always located near the external metacoxal margin. Very few Sphodrini possess a trisetose metacoxa with an additional seta interior of the external posterior seta, these include, some Atranopsina, Bedelinus of Calathina sensu Hovorka (2017a), Anchomenidius Heyden and Casaleius Sciaky & Wrase of Dolichina sensu Hovorka (2017b), and all the fossil species from Eocene amber that we investigated. In these extant and fossil taxa, the seta near the internal metacoxal margin is located at the same place as it was figured for C. elpis by Ortuño and Arillo (2009: 58, fig. 2d). Therefore, we believe that the external setiferous pore on posterior metacoxal area of C. elpis is present but was overlooked by the authors, probably because the seta was broken off or the view obscured, and that the metacoxa of C. elpis is actually trisetose as it is in all the other fossil specimens listed in the present study.
6. Ortuño and Arillo (2009: 58, fig. 2d) further presented a reconstruction drawing of the C. elpis metatrochanter that is asetose. However, the metatrochanters of the holotype specimen actually each are bearing a setiferous pore (Ortuño pers. comm., 2009) as in the diagnosis of Quasicalathus gen. n. (see above).

In addition to the doubtful character states discussed above, the original description of C. elpis provides few indications that lead to recognition of specimens of this species without direct comparison to the holotype. The ten sphodrine specimens from Baltic amber available for us to study, belong to at least two different species of Quasicalathus, and all but one of the diagnostic characters we found to be relevant for these species are absent in the description presented by Ortuño and Arillo (2009). Our interpretation of C. elpis as a member of Quasicalathus gen. n. is based on the assumption that elytral and coxal chaetotaxy was misinterpreted by the authors of the species as discussed above and, additionally, on the following morphological features evident in the photographs of the holotype specimen provided by Ortuño and Arillo (2009: figs 1b, c): pronotal lateral margin moderately narrowed toward base, straight before laterobasal angles, with the latter moderately obtuse (instead of more rounded pronotal lateral margin with more obtuse laterobasal angles in the Baltic amber fossil species Q. agonicollis sp. nov.; see description below). Based on this character, we assume eight of the fossil specimens that are listed under Additional material (below) belong to C. elpis. As a consequence, the redescription of Quasicalathus elpis comb. nov. and information about additional morphological characters that we use to distinguish this species from other Eocene sphodrine species (see descriptions of the new fossil species, below) are based on investigation of these eight additional specimens.

Eight specimens, with the following identification numbers, collection data, preservation state, and syninclusions:

Groehn 4879. Male in Baltic amber, with specimen label data “Groehn 4879”, deposited in Coll. Carsten Gröhn, Hamburg. Size of the piece approx. 15 × 15 × 4 mm (Fig. 1).

Preservation status: The amber is clear but pervaded by numerous air bubbles; most details of external morphology of the embedded fossil are well visible using light microscope (Figs 2, 3). Some parts of the exoskeleton (head, pronotum, elytral apex) are discoloured black. Using micro-CT, the fossilized beetle body yields moderate to low contrast so that parts of its external shape could only be coarsely imaged (Figs 34–37). The aedeagus is not preserved.

Syninclusions: Stellate hairs, additional plant remains, dust particles.

Groehn 7814. Male in Baltic amber, with specimen label data “Groehn 7814”, deposited in Coll. Carsten Gröhn, Hamburg. Size of the piece approx. 35 × 17 × 9 mm (Fig. 5).

Preservation status: The amber is pervaded by numerous flowlines and air bubbles and therefore; the embedded fossil is only visible ventrad and right laterad using light microscopy (Fig. 4). The exoskeleton of the fossil is moderately well preserved and important diagnostic characters could be imaged using micro-CT (Figs 38, 41, 42). The aedeagus is preserved in most parts (Figs 43–46), however, it was completely detached from the terminal abdominal segments during fossilization of the specimen. Most likely it moved through the abdomen and was finally wedged in the tight connection of meso- and metathorax (Figs 39, 40) after drying out of the internal parts of the beetle.

Syninclusions: Stellate hairs, two Nematocera flies, one mite.

Groehn 7889: Female in Baltic amber, with specimen label data “Groehn 7889”, deposited in Coll. Carsten Gröhn, Hamburg. The original size of the amber piece was approx. 35 × 23 × 10 mm and was separated into two pieces (Groehn 7889) in order to get better micro-CT scanning results. The size of the amber piece bearing the calathine fossil measures approx. 30 × 11 × 10 mm (Fig. 6).

Preservation status: The amber is pervaded by an extend flowline attached to the beetle laterally, and a large air bubble is attached to its abdomen ventrally, but most external characters of the beetle are visible using light microscope (Figs 6, 7). The exoskeleton of the fossil is well preserved and could be imaged to show most details using micro-CT (Figs 47–54) including the gonocoxites (Figs 55–57).

Syninclusions: Plant remains, dust particles.

Groehn 7962: Male in Baltic amber, with specimen label data “Groehn 7962”, deposited in Coll. Carsten Gröhn, Hamburg. Size of the amber piece approx. 14 × 10 × 6 mm, irregularly cut and polished (Fig. 10).

Preservation status: The amber is pervaded by numerous flowlines and air bubbles attached to the beetle body, mostly to its ventral surface; the fossil is therefore only partly visible using light microscope (Figs 9–12). Using micro-CT, the fossilized beetle body yields low contrast so that its external shape could only be coarsely imaged (Fig. 58). The aedeagus is not preserved.

Syninclusions: None.

CCHH 952. Female in Baltic amber, with specimen label data “CCHH#952-2”, deposited in the collection of Christel and Hans Werner Hoffeins, Hamburg. Size of the piece approx. 39 × 15 × 7 mm (Fig. 15).

Preservation status: The amber is clear in most parts, a single flowline is attached to the right side of the beetle body, which is clearly visible for most of its length using light microscope (Figs 13, 14); head and abdomen are partly covered by a dirty coating ventrally. The amber was likely altered by autoclaving in order to reduce the milky coating. The results of this process are apparent from the blackened appendages of the beetle that are distinctly deformed (particularly tibiae and tarsi), and from one of the synincluded Nematocera that has a roasted appearance. For details on the effect of autoclaving on amber fossils see Hoffeins (2012). Using micro-CT, the fossilized beetle body yields a contrast so that its external shape could only be coarsely imaged (Fig. 59). This is likewise evidence of prior autoclaving of the piece.

Syninclusions: Two mites, one Brachycera fly, remains of two Nematocera flies, dust particles.

OSAC 265. Male in Baltic amber, with specimen label data “OSAC_2900265”, deposited in the Oregon State University Collection. The original size of the amber piece was 57 × 16 × 4 mm and was separated into three pieces in order to get better micro-CT scanning results. The size of the amber piece bearing the calathine fossil measures approx. 21 × 9 × 4 mm (Fig. 17).

Preservation status: The amber is clear in most parts, some flowlines are attached to the embedded fossil; latter is well visible in most parts of the body using light microscope (Figs 16, 17). Using micro-CT, the fossilized beetle body yields low contrast and therefore, its external shape could only be coarsely imaged (Fig. 60). The aedeagus is not preserved.

Syninclusions: Large number of dust particles in each of the three pieces.

MAIG 76. Female in Baltic amber, with specimen label data “76”deposited in Museum of Amber Inclusions, University of Gdańsk, Poland. Size of the amber piece ca. 33 × 23 × 10 mm, irregularly cut (Fig. 18).

Preservation state: Moderately well preserved due to a large bubble and extensive milky coating attached to the left part of the fossil, resulting in a significant deformation of the beetle body (Fig. 61). A flowline and a corrosion crack are attached to the right side of the beetle body; the apex of the right elytron reaches the amber’s external surface due to a small cavity in the amber piece. Because the fossil yields moderately strong contrast during micro-CT scan, details of its external shape could be imaged apart from the ventral side of the head (Figs 61–63). The genitalic segments are not preserved.

Syninclusions: One tiny insect larva; several air bubbles.

GZG 16185. Male in Baltic amber, with specimen label data “GZG BST 16185” and “G633.G636”, deposited in Geoscience Museum, University of Göttingen, Germany (very probably ex coll. Königsberg). Size of the amber piece 15 × 8.5 × 6 mm, originally with seven polished edges, but fragmented into two pieces of about the same size, with one piece containing most parts of the fossil while the other contains the negative imprint of the left elytron (Fig. 19); the surface of the latter piece bears the inscription “G633.G636”.

Preservation state: Poorly preserved due to amber corrosion; several corrosion cracks pervade the amber surface; amber is markedly darkened with the embedded fossil hardly visible in most views; fossil is partly covered by flowlines, bubbles and milky coating. The fossilized beetle body yields low contrast during micro-CT scan, so that its external shape could only be very coarsely imaged (Fig. 64). The aedeagus is not preserved.

Syninclusions: Stellate hairs, dust particles.

Measurements see Table 2.

SBL: 7.5–8.8 mm (Ø 7.9 mm; n = 7).

Proportions: A3L/HL = 0.40–0.45 (Ø 0.42; n = 11);

EyL/ HW(-) = 0.65–0.79 (Ø 0.72; n = 15);

PW/HW(+) = 1.39–1.58 (Ø 1.50; n = 8);

PW/PL = 1.26–1.33 (Ø 1.29; n = 8);

PW/PWb = 1.03–1.13 (Ø 1.10; n = 8);

PWb/PWa = 1.47–1.61 (Ø 1.52; n = 8);

EW/PW = 1.53–1.64 (Ø 1.29; n = 7);

EL/EW = 1.51–1.62 (Ø 1.55; n = 7);

EpL/EpW = 1.47–1.60 (Ø 1.55; n = 10);

EL/FL = 2.35–2.65 (Ø 2.53; n = 7);

EL/AedL = 4.05 (n = 1).

Head: Microsculpture on disc consists of very small slightly irregular meshes (magnification 80×). In all other characters as described for the new genus, above.

Prothorax: Pronotal lateral margin moderately narrowed toward base, straight or slightly concave before laterobasal angles, angles slightly obtuse (Figs 3, 9, 14, 34, 42, 50, 58–60, 63, 64). Prosternal process with or without apical bead (Figs 37, 38, 51). In all other characters as described for the new genus, above.

Pterothorax: Elytra with basal margin markedly concave and humerus markedly protruded anteriorly; basal margin forming a slightly obtuse angle (100–115°) with lateral margin (Figs 3, 9, 14, 34, 47, 58–60, 61). Elytral striae moderately deeply engraved, intervals moderately convex. In all other characters as described for the new genus, above.

Female genital: Length of apical gonocoxite about 0.18 mm; shape see Figs 55–57. In all other characters as described for the new genus, above.

Aedeagus: Length of median lobe about 1.23 mm; median lobe terminal lamella moderately long and more markedly narrowed just behind its base so that its left margin is markedly concave and its apex slender lingulate (Fig. 46); in lateral view, terminal lamella markedly bent ventrally (Figs 43–45; note that the intensity of ventral bending might also be an artefact of poor preservation). In all other characters as described for the new genus, above.

Quasicalathus elpis (in sense of this paper) differs from Q. agonicollis sp. nov. by larger body (SBL > 7 mm), less obtuse laterobasal angles of pronotum, more concave elytral basal margin, more markedly projected humeri, less obtuse humeral angle (< 120°), longer apical gonocoxites and larger aedeagus. It differs from Q. conservans sp. nov. by the proportionally smaller aedeagus with terminal lamella bent ventrally (Figs 43–45); the left margin of the terminal lamella in dorsal view is significantly concave in Q. elpis (Fig. 46) but almost straight in Q. conservans sp. nov. (Fig. 88).

Male in Baltic amber, with specimen label data “SDEI-Amb-002528”, deposited in Senckenberg Deutsches Entomologisches Institut, Müncheberg, Germany. The original size of the amber piece was 60 × 23 × 7 mm and was separated into three pieces (SDEI Amb-002528 a, b, c) in order to get better micro-CT scanning results. The size of the amber piece bearing the calathine fossil measures approx. 15 × 9 × 4 mm (Fig. 28).

Preservation status: A clear piece of amber with the embedded carabid fossil well visible, however, extensive flowlines are present in front of the head and on the right side of the beetle body. Several parts of the beetle body are additionally covered by a white coating so that details of the exoskeleton are not visible using light microscopy; this includes the dorsal surface of head and pronotum, lateral parts of the elytra, right side of the ventral surface (Figs 29, 30). The external surface of the fossilized beetle body yields low (head, thorax) or relatively moderate contrast (elytra, abdomen) during micro-CT scan and therefore, the anterior part of the body could only be coarsely imaged (Fig. 65). The aedeagus with median lobe and right paramere is moderately well preserved and could partly be imaged using micro-CT data (Figs 68–72); the left paramere provided contrast during CT scan that was too low for reconstruction.

Syninclusions: SDEI-Amb-002528a: seven very tiny insect larva, dust particles; one mite on the carabid fossil near the beetle’s scutellum. SDEI-Amb-002528b: one Myrmicinae ant, three Nematocera flies, stellate hairs, dust particles. SDEI-Amb-002528c: dust particles.

Female in Baltic amber, with specimen label data “GZG BST 16188” and “K2192” (ex coll. Klebs), deposited in Geoscience Museum, University of Göttingen, Germany. Size of the amber piece approx. 12 × 7 × 4 mm, with seven polished edges (Figs 21, 22); one edge bears the inscription “G644”.

Preservation status: The amber stone is clear in most parts but its surface shows several corrosion cracks (Figs 23, 24); the ventral surface of the fossil is completely covered by a milky coating (Fig. 22). The exoskeleton of the fossil is moderately well preserved and could therefore be imaged in most details using micro-CT (Figs 73–75), including the gonocoxites (Figs 76, 77).

Syninclusions: Stellate hairs, dust particles.

The specific identity of this second fossil specimen with the holotype of Q. agonicollis sp. nov., given the current state is difficult to substantiate. This is due to the poor preservation state of the holotype specimen. In the specimen GZG 16188, the pattern of head microsculpture is quite differently developed from that what we found in Q. elpis and the below described Q. conservans sp. nov., however, this character state is unknown for the Q. agonicollis sp. nov. holotype. Therefore, our decision to identify GZG 16188 as Q. agonicollis sp. nov. must be considered provisional. It is based on the following four interspecific diagnostic character states that Q. agonicollis sp. nov. holotype and specimen GZG 16188 share: i) body size small, SBL below 7 mm. ii) pronotal laterobasal angles more markedly obtuse; iii) elytral basal margin moderately concave; iv) humerus slightly protruded with humeral angle more markedly obtuse. Therefore, in the description of Q. agonicollis sp. nov. we separate the descriptions of the Q. agonicollis sp. nov. holotype and the specimen GZG 16188.

Measurements see Table 2.

Standardized body length: 6.7 mm.

Proportions: A3L/HL = 0.45;

EyL/ HW(-) = 0.62;

PW/HW(+) = 1.45;

PW/PL = 1.26;

PW/PWb = 1.17;

PWb/PWa = not available;

EW/PW = 1.60;

EL/EW = 1.55;

EpL/EpW = 1.40;

EL/FL = 2.42;

EL/AedL = 4.07.

Head: Patterns of microsculpture could not be studied. In all other characters as described for the new genus, above.

Prothorax: Pronotal lateral margin more markedly narrowed toward base than in Q. elpis, straight just before laterobasal angles, angles markedly obtuse (Figs 65, 66). Prosternal process with traces of lateral bead evident. In all other characters as described for the new genus, above.

Pterothorax: Elytra with basal margin moderately concave and humerus moderately protruded anteriorly; basal margin forming a more obtuse angle (ca. 125°) with lateral margin (Figs 65, 66). Elytral striae moderately deeply engraved, intervals moderately convex. In all other characters as described for the new genus, above.

Aedeagus: Length of median lobe 1.12 mm. Median lobe terminal lamella almost evenly narrowed from base to apex with side margins almost straight; apex slightly bent ventrally (Fig. 70). In all other characters as described for the new genus, above.

Measurements see Table 2.

Standardized body length: 6.9 mm.

Proportions: A3L/HL = 0.44;

EyL/ HW(-) = 0.65;

PW/HW(+) = 1.46;

PW/PL = 1.26;

PW/PWb = 1.12;

PWb/PWa = 1.40;

EW/PW = 1.63;

EL/EW = 1.53;

EpL/EpW = 1.62;

EL/FL = 2.55.

Head: Microsculpture consists of moderately large isodiametric sculpticells (Fig. 24). In all other characters as described for the new genus, above.

Prothorax: Pronotal lateral margin almost completely rounded, straight just before laterobasal angles, angles markedly obtuse (Figs 23, 25, 73, 74). Prosternal process with traces of an apical bead (Fig. 75). In all other characters as described for the new genus, above.

Pterothorax: Elytra with basal margin moderately concave and humerus moderately protruded anteriorly; basal margin forming a more obtuse angle (ca. 125°) with lateral margin (Figs 23, 73, 74). Elytral striae shallowly engraved, intervals rather flat. In all other characters as described for the new genus, above.

Female genitalia: Length of apical gonocoxite about 0.15 mm; shape see Figs 76, 77; bursa copulatrix is not preserved. In all other characters as described for the new genus, above.

Quasicalathus agonicollis sp. nov. differs from Q. elpis and Q. conservans sp. nov. by the smaller body (SBL < 7 mm), more obtuse laterobasal angles of the pronotum, less concave elytral basal margin, less projected humeri, a more obtuse humeral angle (> 120°) and relatively smaller aedeagus. Based on specimen GZG 16188, Q. agonicollis sp. nov. differs from Q. elpis and Q. conservans sp. nov. additionally by presence of moderately large isodiametric sculpticells on head disc (small and transverse meshes in Q. elpis and Q. conservans sp. nov.) and (from Q. elpis) by the smaller apical gonocoxite (unknown in Q. conservans sp. nov.). Due to the uncertainties in the identification of the Q. agonicollis sp. nov. non-type female specimen (see Remarks above), the latter differential characters need confirmation based on additional material. The eyes of the Q. agonicollis sp. nov. holotype and the GZG 16188 specimen are found to be proportionally smaller [EyL/ HW(-) = 0.62 resp. 0.65] than in Q. elpis (0.72) and the Q. conservans sp. nov. holotype (0.72).

Male in Rovno amber, with specimen label data “SDEI-Amb-002529”, deposited in the Senckenberg Deutsches Entomologisches Institut, Müncheberg, Germany. Size of the amber piece 20 × 10 × 8.5 mm.

Preservation status: The amber is clear but pervaded by numerous small air bubbles and extensive flowlines attached to the embedded fossil that is therefore only partly visible using light microscopy (Figs 32, 33). The exoskeleton of the fossil, including most parts of the aedeagus, is well preserved and, therefore, important diagnostic characters could be reconstructed using micro-CT (Figs 78–89).

Syninclusions: One stellate hair, few tiny dust particles.

Measurements see Table 2.

Standardized body length: 7.3 mm.

Proportions: A3L/HL = 0.44;

EyL/ HW(-) = 0.72;

PW/HW(+) = 1.40;

PW/PL = 1.27;

PW/PWb = 1.11;

PWb/PWa = 1.46;

EW/PW = 1.64;

EL/EW = 1.51;

EpL/EpW = 1.43;

EL/FL = 2.58;

EL/AedL = 3.64.

Head: As described in Q. elpis.

Prothorax: Pronotal lateral margin moderately narrowed toward base, slightly concave before laterobasal angles, angles slightly obtuse (Fig. 78). Prosternal process with traces of a lateral bead (Fig. 85). In all other characters as described for the new genus, above.

Pterothorax: Elytra with basal margin markedly concave and humerus markedly protruded anteriorly; basal margin forming a slightly obtuse angle (ca. 115°) with the lateral margin (Fig. 78). Elytral striae moderately deeply engraved, intervals moderately convex. In all other characters as described for the new genus, above.

Aedeagus: Length of median lobe about 1.33 mm; median lobe terminal lamella moderately long, almost evenly narrowed from base to apex (Fig. 88); terminal lamella almost straight, with tip very slightly bent ventrally (Figs 87, 89). In all other characters as described for the new genus, above.

In external characters, Q. conservans sp. nov. appears identical to Q. elpis, however, it can be distinguished by the male genitalia. The new species differs by the proportionally larger aedeagus (EL/AedL = 3.64 instead of 4.05 in Q. elpis) and by the shape of the median lobe terminal lamella that is nearly evenly narrowed toward the apex if viewed in dorsal aspect and almost straight if viewed laterally (Figs 43, 44 versus 87, 89). Quasicalathus conservans sp. nov. differs from the above-described Q. agonicollis sp. nov. by larger body (SBL > 7 mm), less obtuse laterobasal pronotal angles, the more markedly concave elytral basal margin, more markedly projected humeri, the less obtuse humeral angle (< 120°), and by the larger aedeagus.

Quasicalathus conservans sp. nov. and Q. elpis are, based on current knowledge, indistinguishable in their external characters but differ clearly in the shape and proportions of the male genitalia. Ball and Nègre (1972) and Schmidt (2018) detailed a similar situation found among many species pairs of Mexican and Himalayan Calathus that can only be separated by features of the male genitalia. We hypothesize that Q. elpis and Q. conservans sp. nov. were most likely allopatric species, distributed in geographically separated parts of the Eocene amber forests of northern Europe. Under this hypothesis, Q. elpis was endemic to the more western part of the Eocene forest and was thus fossilized in Baltic amber, while Q. conservans sp. nov. was endemic to the more eastern part of the area and therefore fossilized in Rovno amber. This assumption is consistent with the faunistic data showing that beetle fossils of Baltic and Rovno amber deposits have only few species in common (less than 13%; Matalin et al. 2021).