Archaeonebria inexspectata Schmidt & Kavanaugh, 2019

Schmidt, Joachim, Scholz, Stefan & Kavanaugh, David H., 2019, Unexpected findings in the Eocene Baltic amber forests: Ground beetle fossils of the tribe Nebriini (Coleoptera: Carabidae), Zootaxa 4701 (4), pp. 350-370 : 353-365

Archaeonebria inexspectata Schmidt & Kavanaugh , sp. n.

Type material. Holotype: Male in Baltic amber; Coll. Carsten Gröhn in the collection of the Geological-Palaeontological Institute of the University of Hamburg ( GPIH), now in the Centrum of Natural History , Hamburg (CeNak), with collection number „ GPIH no. 4980, coll. Gröhn no. 7919”. For better investigation of the fossil, the stone was cut in two pieces, with one piece bearing the Nebriini fossil, and has a size of approx. 24 x 6 x 7 mm (irregularly cut) (= „ GPIH no. 4980, coll. Gröhn no. 7919a”, Fig. 1 ); the remaining piece has a size of approx. 35 x 20 x 16 mm (irregularly cut) (= „ GPIH no. 4980, coll. Gröhn no. 7919b”).

Preservation status: The amber is clear but pervaded by several flowlines and partly covered by very fine surface cracks; the embedded Nebriini fossil is extensively covered by flowlines and bubbles adjoining the beetle body ( Figs 2–3 ) and thus, hardly visible using light microscope. The exoskeleton of the specimen and its negative imprint on the inclusion wall is well preserved and could therefore be imaged in detail using micro-CT ( Figs. 4–6 , 31, 32, 34 ), as well as the aedeagal median lobe, except for the weekly sclerotized structures ( Figs 42-49 ).

Syninclusions: One Nematocera fly and a dirt particle in the „ GPIH no. 4980, coll. Gröhn no. 7919a” piece, an additional Nematocera fly in the „ GPIH no. 4980, coll. Gröhn no. 7919b” piece.

Paratype #1: Female in Baltic amber; deposited in the University of California, Museum of Palaeontology , Berkeley , CA, with specimen number UCMP 403984.01 , and locality number IP 15208 ( Fig. 9 ). Size of the piece approx. 31 x 20 x 8 mm .

Preservation status: The amber is clear, pervaded by very few flowlines, partly covered by very fine surface cracks; the embedded Nebriini fossil is partly covered by milky coating and a small bubble adjoining the dorsal surface of the beetle body ( Fig. 7 ). Parts of the metatarsi are cut and thus lost. The exoskeleton of the Nebriini fossil and its negative imprint on the inclusion wall are moderately well preserved and could therefore be imaged in most details using micro-CT ( Figs. 11–13 ). Traces of the fossilized gonocoxites could also be imaged.

Syninclusions: One Trichoptera, three Nematocera flies (two of which are preserved in mating position), one Coleoptera : Scirtidae , stellate hairs, dirt particles.

Paratype #2: Female in Baltic amber; no. CCHH #952- 1 in the collection of Christel and Hans Werner Hoffeins , Hamburg, Germany (later to be deposited at the Senckenberg Deutsches Entomologisches Institut , Müncheberg, Germany) ( Fig. 16 ). Size of the piece approx. 13 x 7.5 x 7 mm .

Preservation status: The amber is clear, partly pervaded by very few flowlines; the embedded Nebriini fossil is partly covered by milky coating adjoining head and elytra ( Fig. 14 ), and extensively covered by milky coating and small bubbles adjoining the ventral surface of the beetle body ( Fig. 15 ). Left antennomeres 9–11 and right metatarsomere 5 are cut and thus lost. The fossilized exoskeleton of the specimen is in parts shrunken and thus dissociated from the inclusion wall ( Fig. 19 ). However, most details of diagnostic importance of the external morphology could be reconstructed based on both, the remains of the fossilized exoskeleton and the negative imprint of the beetle body on the inclusion wall, using micro-CT ( Figs 18–20 , 29 ) including the gonocoxites ( Figs 50–53 ).

Syninclusions: No syninclusions except for a few dirt particles.

Paratype #3: Female in Baltic amber, deposited in the amber collection of the Senckenberg Deutsches Entomologisches Institut , Müncheberg, Germany ( SDEI) ( Fig. 23 ). Size of the piece approx. 24 x 14 x 5 mm .

Preservation status: The amber attached to the embedded Nebriini fossil is pervaded by several flowlines, dorsally and ventrally of the fossil; its ventral surface is almost fully covered by milky coating ( Fig. 22 ). Due to the extensive flowlines, micro-CT scans resulted in low contrasts between amber and fossil particularly on its dorsal surface ( Fig. 24 ).

Syninclusions: Two Nematocera flies, wing remains of an additional Nematocera fly, stellate hairs, dirt particles.

Description. Color: All specimens appear unicolored dark throughout, with pronotum and elytra markedly shiny. No metallic reflection is evident.

Microsculpture: Not visible on any part of the male holotype, and on the head surfaces of any of the female paratypes; on pronotum and elytra of females with very finely impressed small transverse meshes (visible at magnifications of> 60x).

Measurements: Standardized body length 6.4 (holotype, paratype #1) to 7.2 mm (paratype #3). Length of aedeagal median lobe 0.94 mm (holotype). For additional measurements see Tab. 2 .

Proportions, given for holotype; paratype #1; paratype #2; paratype #3:

PW/HW = 1.36; 1.34; 1.41; 1.43.

PW/PL = 1.59; 1.65; 1.62; 1.65.

PW/PWb = 1.03; 1.07; 1.08; 1.13.

PWb/PWa = 1.36; 1.27; 1.28; 1.22.

EW/PW = 1.06; 1.22; 1.18; 1.18.

EL/EW = 1.50; 1.50; 1.46; 1.47.

EL/FL = 2.00; 2.10; 2.05; 2.16.

LPL3/LPL2 (min–max) = 1.21–1.23; 1.19–1.24; not measurable in paratype #2; 1.26–1.28.

EL/AedL = 4.15 (holotype).

Variation: The pronotum is less transverse, and its extension is larger, in the male holotype than in the three female specimens. In the female paratype #3 the pronotum is less constricted towards the base than in the other specimens, and its legs are slightly shorter.

Etymology. The species epithet, inexspectata , is a Latin adjective meaning “unexpected”, referring to unexpected occurrence of a nebriine carabid in Baltic amber.

Figures

FIGURES 1–3. Archaeonebria inexspectata gen. n., sp. n., light microscopic images of the holotype. Fig. 1, general view with contours of the amber piece. Fig. 2, right lateral aspect of the embedded specimen. Fig. 3, dorsal aspect.

FIGURES 4–6. Archaeonebria inexspectata gen. n., sp. n., volume rendering of the holotype. Fig. 4, dorsal aspect. Fig. 5, right lateral aspect. Fig. 6, ventral aspect.

FIGURES 31–36. Archaeonebria inexspectata gen. n., sp. n., volume rendering of the holotype (Figs 31, 32, 34) and paratype #2 (Fig. 33, 35, 36). Fig. 31, head, dorsal aspect; the arrows point to the insertions of the labral setae, clypeal seta, and supraorbital seta. Remark: Note the deformation of the labral apical margin with respect to its negative imprint on the inclusion wall, which represents its original state. Fig. 32, head, ventral aspect; the arrows point to the insertions of the setae on mentum and submentum. Figs 33, 34, mouthparts, apicoventral aspect of different specimens using different greyscale thresholds. Figs 35, 36, separated images of the ligula with the completely fused paraglossae (Fig. 35, ventral aspect; Fig. 36, apicoventral aspect). Abbreviations: ant = antenna; dp = dust particles; la = lacinia; lig = ligula; lig-a = apex of ligula; lp-l = left labial palpus; lp-r = right labial palpus; m = mentum; md-l = left mandible; md-r = right mandible; mp-l = left maxillary palpus; mp-r = right maxillary palpus; mx = maxilla; n = negative imprint of the labral margin; p = shrunken remains of the labral margin; pgl = paraglossa.

FIGURES 42–53. Archaeonebria inexspectata gen. n., sp. n., volume rendering of the aedeagus of the holotype using different grey scale thresholds (Figs 42–49), and of the female ovipositor of paratype #2 (Figs 50–53; the ovipositor was separated by the segmentation function of Amira software in Figs 51–53). Figs 42, 45, left lateral view. Figs 43, 46, view slightly diagonal from behind, frontally to the apical lamella. Figs 44, 47, right lateral view. Fig. 48, frontal view towards median lobe base. Fig. 49, view from posterad towards median lobe apex. Fig. 50, section of the female abdomen in ventral view. Fig. 51, ovipositor in ventral view. Fig. 52, postero-left lateroventral view. Fig. 53, dorsal view.Abbreviations: al = apical lamella of aedeagal median lobe; ap = lanceolate apophysis of left paramere; ds = dorsal row of spiniform setae on the edge of the fused apical and basal gonocoxites; g = gut; gc 1 = basal gonocoxite; gc 2 = apical gonocoxite; ltg = laterotergite; mtg = mediotergite; o-a = extreme apex of apical ostium of median lobe; o-b = extreme base of apical ostium; pm-l = left paramere; pm-r = right paramere; se = sagittal aileron; sp = sensory pit; vs = ventral row of spiniform setae (only shown on right basal gonocoxite);?vs = the pore marks the insertion of a probable additional spiniform seta of the ventral series.

FIGURES 7–10. Archaeonebria inexspectata gen. n., sp. n., light microscopic images of the paratype #1. Fig. 7, dorsal aspect of the embedded specimen. Fig. 8, ventral aspect. Fig. 9, general view with contours of the amber piece, showing several embedded insects (see text for details); the arrow points to the position of the embedded Archaeonebria specimen. Fig. 10, basal part of the left hindleg; the arrows point to the positions of the anterior and posterior metacoxal setae. Abbreviations: mcx = metacoxa; mtr = metatrochanter; w-l = left hindwing; w-r = right hindwing.

FIGURES 11–13. Archaeonebria inexspectata gen. n., sp. n., volume rendering of the paratype #1. Fig. 11, dorsal aspect. Fig. 12, left lateral aspect. Fig. 13, ventral aspect. Remark: The wave-like lines covering some parts of the beetle body represent shading artifacts.

FIGURES 14–17. Archaeonebria inexspectata gen. n., sp. n., light microscopic images of the paratype #2. Fig. 14, dorsal aspect of the embedded specimen. Fig. 15, right lateral aspect. Fig. 16, general view with contours of the amber piece. Fig. 17, right antennomeres II–VI.

FIGURES 18–20. Archaeonebria inexspectata gen. n., sp. n., volume rendering of the paratype #2. Figs 18, 19, dorsal aspect using different grey scale thresholds (Fig. 18 shows the negative imprint of the beetle body on the inclusion wall; Fig. 19 shows the fossilized exoskeleton which is partly dissociated from the inclusion wall). Fig. 20, left lateral aspect. Remark: The partly darkened areas near caudal apex of the beetle body represent shading artifacts.

FIGURES 27–30. Archaeonebria inexspectata gen. n., sp. n., light microscopic images of paratypes #1 (Figs 27, 28, 30) and #2 (Fig. 29). Fig. 27, prothorax and part of the head, ventral aspect. Fig. 28, left labial palpus; the arrows point to the three setae inserted on the penultimate palpomere. Fig. 29, left metatarsomeres II–V. Fig. 30, abdomen and left metafemur, ventral view; the arrows point to the insertions of the two dorsoapical setae of the femur, the setae near apical margins of the sternites IV and V (if visible; the setae on sternite VI are shadowed by the right metatibia), and the two pairs of setae on sternite VII. Abbreviations: ce = compound eye; gu = gula; lp-2, 3 = labial palpomeres 2, 3; m = mentum; mf = metafemur; pcx = procoxa; pep = proepisternum; pst = prosternum; st-IV–VII = abdominal sternites IV–VII.

FIGURES 21–23. Archaeonebria inexspectata gen. n., sp. n., light microscopic images of the paratype #3. Fig. 21, dorsal aspect of the embedded specimen. Fig. 22, ventral aspect. Fig. 23, general view with contours of the amber piece.

FIGURES 24–26. Archaeonebria inexspectata gen. n., sp. n., volume rendering of the paratype #3. Fig. 24, dorsal aspect. Fig. 25, left lateral aspect. Fig. 26, ventral aspect.

Tables

TABLE 2. Measurements [µm].

	holotype	paratype “#1”	paratype “#2”	paratype “#3”
length of head	939	896	922	1013
width of head	1810	1674	1859	1846
length of pronotum	1547	1363	1624	1603
width of pronotum	2461	2248	2624	2644
pronotal apical width	1762	1694	1899	1922
pronotal basal width	2390	2096	2429	2338
length of left / right elytron	3904 / 3892	4070 / 4117	4483 / 4500	4574 / 4574
width of left / right elytron	1252 / 1345	1381 / 1365	1522 / 1564	1577 / 1544
length of left / right labial palpomere 2	390 / 385	373 / 370	not observable	369 / 370
length of left / right labial palpomere 3	478 / 466	461 / 442	not observable	466 / 476
length of left / right metafemur	1937 / 1949	1935 / 1955	2194 / 2027	2120 / 2070