Praeanchodemus, Will, 2017

Will, Kipling, 2017, Description of the first flightless platynine ground beetle preserved in Baltic amber (Coleoptera: Carabidae), Zootaxa 4318 (1), pp. 110-122 : 111-114

Praeanchodemus gen. n.

Type species. Praeanchodemus punctaticeps Sp. n., foSSil SpecieS from the Eocene Baltic amber.

Description. AS the new genuS iS monotypic and baSed on a Single Specimen, neither the interSpecific nor intraSpecific variability of characterS iS known. Herein, we deScribe the new taxon in detail under the genuS deScription and only include colour and dimenSionS of the body partS in the SpecieS’ deScription below.

Body length: Rather Small compared with average in Platynini : 5.4 mm in type Specimen.

MicroSculpture: On head markedly contraSting with microSculpture patternS on pronotum and elytra: DorSal Surface of head with large and deeply engraved lineS forming iSodiametric SculpticellS; pronotum and elytra with much Smaller SculpticellS that are diStinct only on SideS, near baSe of pronotum, and within elytral Striae; pronotal diSc and elytral intervalS without viSible microSculpture even at magnification 100x.

Head: Size and proportionS averaged for Platynini , in dorSal view not conStricted towardS neck. DiSc convex, throughout with deep coarSe punctureS ( FigS 1 , 5 , 18 ). MandibleS ( FigS 6–7 ) Slender, with Scrobe aSetoSe. Labrum 6-SetoSe, clypeuS with a Single Seta each Side. EyeS moderately large, moderately protruded ( Fig. 5 ); templeS rather long ( Fig. 15 ), 0.3 timeS of eye length, weakly wrinkled to neck; Supraorbital furrow indiStinct, two Supraorbital Setae preSent ( Fig. 5 ). Apical tooth of mentum Simple; Setae near mentum tooth Small, inSerted very cloSe together, immediately baSad of mentum tooth, Submentum with two pairS of lateral Setae, outer pair diStinctly Smaller ( FigS 6–7 ). StipeS with a large Seta externally near baSe; penultimate article of maxillary palpuS medially biSetoSe; ligular Sclerite with two Setae near apical margin. Antennae Slender, pubeScent from fourth antennomere onwardS, Scape not markedly enlarged, Same length aS third antennomere, with one Seta on dorSal Side; pedicel 0.6 timeS aS long aS Scape, with a primary apical Seta on ventral Side and a finer apical Seta each on dorSal and ventral SideS; third antennomere without Setae in addition to normal ring of apical Setae.

Prothorax: In dorSal view Subcordate-Subquadrate, moderately tranSverSe, broadeSt in middle, with baSal margin Slightly broader than apical margin; SideS evenly rounded in anterior 7/8 and Slightly concave near laterobaSal angleS ( Fig. 5 ). Anterior margin moderately concave with front angleS diStinctly protruded, Shortly rounded; baSal bead fine, interrupted in middle. PoSterior margin Straight in middle, with external Sixth markedly bent anteriad; laterobaSal angleS markedly Shifted anteriad, obtuSe, not protruded laterally; baSal bead broadly interrupted in middle. DiSc convex, Slightly but diStinctly rugoSe; baSe coarSely rugoSe, without punctureS. Median longitudinal impreSSion moderately deep in middle, diSappearing near apex and baSe; both anterior and poSterior tranSverSe impreSSionS indiStinct. Lateral gutter narrow throughout, very Slightly widened towardS baSe; laterobaSal depreSSionS rather Shallow. Both lateral and laterobaSal Setae preSent, with laterobaSal Setae located beSide lateral gutter at anterior 1/3 of pronotal length, and laterobaSal Setae located on margin ( Fig. 5 ). ProSternum and proepiSternum Smooth, proSternal proceSS not marginated ( Fig. 12 ); anterior coxal cavitieS cloSed poSteriorly.

Pterothorax: Elytra markedly convex on diSc ( Fig. 16 ), flattened towardS baSe, elongate-ovate in dorSal view, with ShoulderS moderately broad, humeral angleS and apex Shortly rounded ( FigS 10–11 ). BaSal margin concave, protruded towardS Scutellum and humeruS aS well. All Striae deeply impreSSed, impunctate ( Fig. 10 ); paraScutellar Stria moderately long, not connected to firSt Stria; firSt Stria complete to baSe; intervalS moderately convex; fifth interval not impreSSed at apex. ParaScutellar Seta at baSe of firSt Striae, three diScal Seta on third interval, and Subapical Seta near end of Seventh Stria preSent ( FigS 9 , 11 ), with anterior diScal Seta located between anterior fifth to Sixth of elytral length, adjoined to third Stria, middle Seta located Slightly behind elytral middle, adjoined to third Stria, and poSterior Seta located at poSterior elytral Seventh, adjoined to Second Stria; diScal Setae not Set in foSSae. Umbilicate SerieS conSiStS of 15 Setae adjoining eighth Stria, with diStance between 6th and 7th Seta Slightly larger ( Fig. 16 ). MetepiSternum Smooth, Short, with outer margin Slightly longer than anterior margin ( FigS 12 , 16 ). Hind wingS reduced to Short StubS.

LegS: Rather Short. All trochanterS with a Single Seta on external Surface. MeSocoxa with a Single ridge Seta ( Fig. 12 ); metacoxa biSetoSe, without Seta near internal margin ( Fig. 13 ); anterior metacoxal SulcuS Straight. Profemur with a Single Seta on ventral Surface and with two rowS of Six Short Setae on anterior Surface; meSofemur with two Setae on ventral Surface and with two rowS of nine Short Setae on anterior Surface; metafemur with two Setae on ventral Surface ( Fig. 13 ), with dorSal Surface Smooth even near apex. Protibia not modified, with external Surface Smooth. FirSt and Second tarSomereS each with a pair of dorSoapical Setae, latter lacking on diStal tarSomereS; fourth tarSomereS of all legS Simple, with ventro-apical lobeS very Short, with pair of lateroapical Setae preSent and without dorSoapical Setae; ventral SurfaceS of fifth tarSomereS Smooth; clawS Simple. PreSence of lateral longitudinal grooveS on dorSal SurfaceS of tarSomereS could not be confirmed.

Abdomen: Abdominal SterniteS Smooth beSide normal Setation; V–VI with one, VII with two (female) pairS of Setae near apical margin ( Fig. 14 ).

Female genitalia: Form of gonocoxiteS aS typical of moSt Platynini ( Fig. 17 ); baSal gonocoxiteS moderately Stout, apical gonocoxiteS Slender cone-Shaped, very Slightly bent outwardly, with Subapical SetoSe organ preSent; chaetotaxy and internal genital tract could not be Seen nor viSualized.

Etymology. A compound word, baSed on the Latin prefix “prae-“ and the name of the platynine taxon Anchodemus MotSchulSky, 1864. The name of the new genuS particularly referS to the externally Similar taxon Paranchodemus Habu, 1978 , which waS deScribed aS SubgenuS of Anchodemus and elevated to genuS level by Liebherr (1989a).

Differential diagnosis and relationships. A Small repreSentative of Platynini with rather Short legS, which iS eaSily diStinguiShed from all other genera of that tribe by the following combination of external characterS:

1) Setae near mentum tooth inSerted cloSe together, immediately baSad of mentum tooth.

2) DiSc of head throughout with deep coarSe punctureS.

3) Head lacking diStinct neck conStriction.

4) MicroSculpture patternS markedly contraSting on different body partS, with large and deeply engraved lineS

forming iSodiametric SculpticellS on head and very indiStinct SculpticellS on pronotal and elytral diScS.

5) Pronotal lateral gutter narrow throughout, laterobaSal depreSSionS Shallow.

6) Metacoxa biSetoSe, without Seta near internal margin.

7) Profemur with a Single Seta, meSofemur with only two Setae on ventral Surface.

8) Metafemur dorSally without apical Setae.

9) All legS with fourth tarSomere dorSoapical Setae lacking.

10) All legS with fifth tarSomere Smooth on ventral Surface.

The poSition of mentum Setae iS conSidered an important indication for SpecieS-group relationShipS ( Schmidt 2001a). By far, moSt lineageS of platynine ground beetleS have a Single pair of Setae inSerted caudally of the deep, apical inciSionS of the mentum, laterally of the apical tooth, and thuS, the inSertion pointS of the mentum Setae are located rather diStant from each other (See Schmidt 2001a: FigS 12, 14 , 16 ). In contraSt, the character State obServed in the foSSil Praeanchodemus gen. n. (character State 1) iS preSent in only Six terminal Platynini lineageS, and iS conSidered apomorphic. However, given the current State of knowledge, there iS no evidence for cloSe relationShipS of theSe lineageS ( Schmidt 2000, 2001a). It iS thuS likely that the adjacent poSition of the mentum Setae evolved within the tribe two or more timeS independently. In the following, the Six relevant lineageS are diScuSSed in more detail and compared with the new foSSil taxon.

Limodromus MotSchulSky, 1850 : Occurrence of thiS genuS in the foSSil fauna of the Eocene Baltic amber foreStS waS confirmed recently ( Schmidt 2015). Monophyly of Limodromus iS well Supported by highly derived morphology of the aedeagal median lobe that iS unique within Platynini ( Schmidt 2000, 2005). BecauSe deScription of Praeanchodemus gen. n. iS baSed on a female Specimen the relevant character StateS have not been examined. However, in external characterS, repreSentativeS of Limodromus are eaSily diStinguiShed from Praeanchodemus gen. n. by the head, which iS diStinctly conStricted towardS neck, and by the pronotum, which iS large, cordate, and haS lateral gutter and laterobaSal grooveS very broadly developed. WhereaS in Praeanchodemus gen. n. a baSal conStriction of the head capSule iS lacking, the pronotal lateral gutter iS markedly Small and the laterobaSal depreSSionS are Shallow (See character StateS 3 and 5). In addition, patternS of micro- and macroSculpture of the dorSal Surface of the body are very differently developed in Limodromus with reSpect to Praeanchodemus gen. n. (See character StateS 2 and 4) and, in Limodromus SpecieS the metafemurS bear dorSoapical Setae that repreSent the pleSiomorphic character State, which are completely reduced in Praeanchodemus gen. n. (See character State 8). ConSequently, due to the lack of apparent SynapomorphieS a cloSe relationShip of Limodromus and the Praeanchodemus gen. n. appear unlikely.

Anchomenus clade sensu Liebherr (1991; compriSing the genera Anchomenus Bonelli, 1810 (sensu lato), Elliptoleus BateS, 1882, Sericoda Kirby, 1837 , Tetraleucus CaSey, 1920 ): The hypotheSiS of monophyly for thiS diverSe clade iS baSed on derived character StateS of the female internal genital tract. ThiS part of the tract, however, iS not preServed in the foSSil Specimen. Within the Anchomenus clade an adjacent poSition of mentum Setae aS developed in Praeanchodemus gen. n. (character State 1) probably evolved independently Several timeS becauSe it iS obServed in the weStern Palearctic SpecieS of Anchomenus ( A. cyaneus Dejean, 1828 , A. dorsalis Pontoppidan, 1763 , A. kurnakovi KryzhanovSkij, 1983 , and the A. dohrnii SpecieS group sensu Schmidt 2014), aS well aS in Some SpecieS of Elliptoleus BateS, 1882, and Sericoda Kirby, 1837 . SpecieS of theSe groupS, however, differ by their leg chaetotaxy: pro- and meSofemur with additional Setae on ventral SurfaceS, metafemur dorSally with apical Setae developed, and all legS with the fifth tarSomere SetoSe on ventral Surface; the pleSiomorphic (character State 7) and reSpectively derived character StateS (8, 10) aS developed in Praeanchodemus gen. n.. In addition, in the Anchomenus clade, patternS of micro- and macroSculpture of the dorSal Surface of the body are remarkably different from thoSe of Praeanchodemus gen. n. In three SpecieS, Anchomenus virescens MotSchulSky, 1864 from Middle ASia, A. leucopus BateS, 1873 from Far EaSt ASia, and A. yukihikoi Habu, 1962 from Japan, a faint denSe puncturing iS developed on head and pronotum (in A. virescens on whole body Surface) that iS aSSociated with +/- diStinct microSetation. However, thiS puncturing doeS not appear to be homologouS to the diSSimilar, coarSe and irregularly arranged punctureS, which iS not aSSociated with Setation, on diSc of head found in the foSSil Praeanchodemus gen. n. ConSequently, there iS no certain evidence for cloSe relationShipS of the Anchomenus clade and Praeanchodemus gen. n.

Clade of Agonum Bonelli, 1810 + Agonidium Jeannel, 1948 : For thiS clade, an adjacent poSition of mentum Setae iS conSidered a pleSiomorphic character State with multiple tranSformationS to a more lateral poSition ( Liebherr & Schmidt 2004). SpecieS of thiS clade Share the Shape of the head, with an indiStinct neck conStriction, with Praeanchodemus gen. n. (character State 3), however, they differ from the latter by the more derived Shape of pronotum with more rounded hind angleS. DeSpite of the pro- and meSofemoral Setation in Some SpecieS, in the Agonum + Agonidium clade chaetotaxy patternS of legS are pleSiomorphic to what iS obServed in Praeanchodemus gen. n. Although a few SpecieS Share one or two of the above liSted derived character StateS 6 and 8-10 together with Praeanchodemus gen. n., thiS iS moSt likely the reSult of convergent evolution. AlSo in the Agonum + Agonidium clade patternS of micro- and macroSculpture of the dorSal SurfaceS of the body are very differently developed from thoSe of Praeanchodemus gen. n. ConSequently, there iS no clear evidence for SynapomorphieS and thuS cloSe relationShipS of the Agonum - Agonidium clade and Praeanchodemus gen. n.

Platynus Bonelli, 1810 in SenSe of Schmidt (2000) (= the hypolithos group in SenSe of Liebherr 1989b): Monophyly of Platynus iS well Supported by the highly derived Shape and the Sclerotization patternS of the Spermatheca and the endophalluS, reSpectively. TheSe character StateS are unique within Platynini ( Liebherr 1989b) . However, while the foSSil Specimen iS a female, itS genital tract iS not Sufficiently preServed and So genital characterS cannot be conSidered here. Externally, SpecieS of Platynus are characterized by a pair of reddiSh brown SpotS on neck which are probably baSed on different Sclerotization patternS of the head capSule ( Schmidt 2000). ThiS character State iS not realized in Praeanchodemus gen. n. Platynus additionally differS from the foSSil SpecieS by having the head with a diStinct neck conStriction, with the pronotum having the lateral gutter and laterobaSal grooveS broadly developed, by a more pleSiomorphic chaetotaxy of the legS, and by different patternS of micro- and macroSculpture of the dorSal SurfaceS of the body. A cloSe relationShip of Praeanchodemus gen. n. and Platynus iS thuS very unlikely.

Paranchodemus Habu, 1978 and the Rhadine - Tanystoma lineage sensu Liebherr (1985, 1986, 1989b): Monophyly of the EaSt ASian Paranchodemus iS well Supported by Several SynapomorphieS of the SpecieS ( Liebherr 1989a). The author aSSumeS cloSe relationShipS of Paranchodemus with the North American genera Rhadine LeConte, 1848 and Tanystoma MotSchulSky, 1865 baSed on propoSed SynapomorphieS of the female genital tract (broad duct of the Spermathecal) and tarSal chaetotaxy (fourth tarSomere with dorSoapical Setae lacking). The latter character iS alSo obServed in Praeanchodemus gen. n. (character State 9). Remarkably, the foSSil taxon haS three additional derived characterS in common with Paranchodemus which, however, are not developed in the Rhadine - Tanystoma lineage: neck punctate (character State 2); pronotal lateral gutter narrow (character State 5); all legS with tarSomere 5 Smooth on ventral Surface (character State 10). One additional derived character Praeanchodemus gen. n. ShareS together with Paranchodemus and Tanystoma , but not with Rhadine : metafemur dorSally without apical Setae (character State 8). It thuS appearS poSSible that Praeanchodemus gen. n. iS SiSter group of Paranchodemus , and both theSe taxa together with Tanystoma form a monophyletic group. However, the phylogenetic Signal of the character StateS mentioned above iS unknown or weak, Since all but one (the punctate neck) were independently developed in other Platynini lineageS. In addition, Paranchodemus differS markedly from the foSSil Praeanchodemus gen. n. by a large Set of external characterS, e.g., much larger body Size, preSence of a diStinct neck conStriction, finely impreSSed SculpticellS of microSculpture on diSc of head, bifid mentum tooth, lack of the outer pair of Setae at Submentum, lack of Setae at pronotal laterobaSal angleS, preSence of additional Setae at apex of the Seventh elytral Stria, preSence of additional Setae near apical marginS of abdominal SegmentS V- VII, and by the Shape of the apical gonocoxite which iS markedly broad and Stout. Tanystoma differS markedly by Short mandibleS, Stout mentum tooth, wide pronotal lateral gutter, triSetoSe metacoxa, preSence of additional Setae on ventral Surface of pro- and meSocoxae, SetoSe ventral Surface of fifth tarSomere, and preSence of microSetation on body Surface.

ConSequently, although we point to Some evidence from external morphology that Praeanchodemus gen. n. could be part of a lineage compriSing the recent genera Paranchodemus , Rhadine , and Tanystoma , certain SynapomorphieS were not found and thuS, the actual relationShipS of the foSSil taxon remainS unSettled.

Figures

FIGURE 18. Praeanchodemus punctaticeps sp. n., reconstruction of the external shape in dorsal View.

FIGURES 1 – 4. Praeanchodemus punctaticeps sp. n., light microscopic images of the holotype. Fig. 1, dorsal aspect. Fig. 2, Ventral aspect. Fig. 3, left lateral aspect. Fig. 4, general View with contours of the amber piece.

FIGURES 5 – 9. Praeanchodemus punctaticeps sp. n., Volume rendering of the holotype. Fig. 5, anterior part of body, dorsal aspect; the arrows point to the insertions of the supraorbital setae, pronotal lateral and laterobasal seta, and parascutellar seta. Figs 6 – 7, Ventral aspect of head using different grayscale thresholds; the arrows point to the insertions of the setae at the mentum tooth and at the submentum. Fig. 8, anterior part of body, right dorsolateral aspect. Fig. 9, elytra, View from caudat; the arrows point to the insertions of the third discal seta and the subapical seta. Note in Figs. 8 – 9 that the fossilized exoskeleton is markedly dissociated from the inclusion wall (= the negatiVe imprint of the beetle body).

FIGURES 15 – 17. Praeanchodemus punctaticeps sp. n., Volume rendering of the holotype. Figs 15, anterior part of body, right lateral aspect. Fig. 16, posterior part of body, right lateral aspect; the arrows point to the insertions of the setae of the elytral umbilical series. Fig. 17, seVenth abdominal segment and caudal parts of the female genital using different grayscale thresholds (17 a – b), and reconstructed shape of the gonocoxites (17 c). AbbreViations: acxt: apical gonocoxite; bcxt: basal gonocoxite.

FIGURES 10 – 14. Praeanchodemus punctaticeps sp. n., Volume rendering of the holotype. Figs 10 – 11, elytra using different grayscale thresholds; the arrows point to the insertions of the discal setae (note that the fossilized left elytron is markedly dissociated from the inclusion wall). Fig. 12, left lateral aspect of pro-, meso-, and metathorax; the arrow points to the insertion of the seta at the mesocoxal ridge. Fig. 13, coxa, trochanter, and femoral base of hind legs; the arrows point to the insertion points of setae (see text for details). Fig. 14, abdominal sternites V-VII; the arrows point to the insertions of the two pairs of setae near apical margin of the seVenth sternite. AbbreViations: mep: metepisternum; mscx: mesocoxa; mtcx: metacoxa; pcx: procoxa.