The set of characters used in the analyses is mainly based on a list presented in Beutel et al. 12 , a study focused on the systematic position of Tetraphalerus in Archostemata. More detailed information on character states was gained from the observation of specimens and original descriptions in the literature 2 3 7 8 17 18 20 23 24 30 31 32 33 34 35 .

0. The dorsal head surface longitudinal bulge or keel: (0) present; (1) absent. A distinct and sharp longitudinal bulge or keel is present on the dorsal side of the head of Notocupoides, Notocupes, Rhabdocupes, Zygadenia, Eurydictyon and Amblomma 33 , and also in Permocupes and Platycupes 3 .

1. Posteromesal dorsal protuberance of the head 12 : (0) present; (1) absent. A moderately convex protuberance is present in the cupedid genus Platycupes, in Tetraphalerus 12 and Notocupoides, Eurydictyon, Notocupes, Rhabdocupes, Zygadenia, Lithocupes, Liassocupes and Amblomma 3 19 . It is not recognizable in extant species of Omma and the fossil genera Cionocoleus, Pareuryomma, Odontomma and Brochocoleus 19 .

2. Median epicranial (=coronal) suture: (0) present; (1) absent. The epicranial suture is not visible and apparently absent in Omma 7 12 and Cionocoleus 36 . It is distinct in the genera Notocupoides, Notocupes, Rhabdocupes, Zygadenia, Eurydictyon, Amblomma, Tetraphalerus, Pareuryomma, Brochocoleus, Permocupes and Cupedidae 3 12 19 33 .

3. Head with ventrolateral antennal grooves: (0) absent; (1) present. The presence of lateral longitudinal grooves on the ventral side of the head is an autapomorphy of Tetraphalerus 12 . They are absent in Omma and Cupedidae, and are also missing in fossil ommatid taxa.

4. Gular sutures: (0) complete, reaching hind margin of head capsule; (1) incomplete, not reaching hind margin of head capsule; (2) absent. The gular sutures of Platycupes and Permocupes, and the fossil ommatid genera Eurydictyon, Notocupoides, Notocupes, Rhabdocupes, Zygadenia and Amblomma reach the hind margin of the head capsule 3 33 . They are incomplete in Omma 6 7 . The gular sutures are not recognizable in extant species of Tetraphalerus 12 .

5. Shape of gula: (0) sutures not converging posteriorly; (1) sutures converging posteriorly. Diverging in Platycupes and some fossil ommatids such as Notocupoides, Rhabdocupes, Notocupes, Zygadenia and Amblomma, and also in Permocupes 3 33 . Converging in Omma 6 .

6. Frontoclypeal suture: (0) present; (1) absent. Usually absent in extant Archostemata 12 , but present in Notocupoides, Rhabdocupes, Notocupes, Eurydictyon and Amblomma, and also in Permocupes 3 33 .

7. Ratio of labrum to clypeus: (0) labrum strongly transverse, as wide as clypeus (ratio 1); (1) labrum distinctly narrower than clypeus (ratio less than 1). The labrum of Amblomma, Brochocoleus, Pareuryomma, Odontomma, Cionocoleus and Lithocupes 3 19 is distinctly narrower than the clypeus 3 , whereas the labrum of Tetraphalerus and Permocupes is strongly transverse and as wide as the clypeus 12 . This character is not visible in some fossil taxa. The labrum fused with the clypeus in the genus Omma.

8. Anterior margin of labrum: (0) distinctly convex; (1) truncate. The anterior margin of the labrum is distinctly convex in the genera Notocupoides, Rhabdocupes, Notocupes, Eurydictyon, Amblomma, Lithocupes, Cionocoleus, Odontomma, and Omma 3 7 33 , and also in Permocupes and Platycupes 3 . It is truncate in the genus Pareuryomma, Brochocoleus and Tetraphalerus 12 .

9. Length of antenna: (0) reaching mesothorax posteriorly; (1) not reaching hind margin of prothorax posteriorly. The antennae are strongly elongated in Cupedidae, but moderately long or even short in most members of Ommatidae 7 .

10. Length of pedicel: (0) not distinctly shortened; (1) distinctly shortened. Not distinctly shortened, nearly as long as the third antennomere in Notocupoides, Eurydictyon, Pareuryomma and also in Permocupes 3 12 19 . It is greatly shortened in the other taxa under consideration.

11. Length of third antennomere: (0) not elongated; (1) distinctly elongated. The third antennomere of Permocupes and Platycupes, and of the genera Notocupoides, Rhabdocupes, Notocupes, Zygadenia, Eurydictyon and Pareuryomma is moderately long, about as long as the fourth. It is distinctly elongated, longer than the fourth antennomere in the other ommatid tribes 12 .

12. Apical flagellomere: (0) apically rounded, appearing inflated; (1) parallel-sided. The apical flagellomere of Pareuryomma (Figure 1B), Tetraphalerus decorosus (Figure 2B) and Permocupedidae 3 is apically rounded and appears inflated. It is parallel-sided and slender in the other genera of Ommatidae and Cupedidae.

13. Length of mandible: (0) short or moderately long, largely covered by labrum in repose; (1) very elongate and protruding in resting position. Moderately long or short and largely covered by the labrum in the resting position in most extant Archostemata and most of the fossil taxa. Exceptionally long and distinctly protruding in Tetraphalerus 12 , Cionocoleus 19 , Omma gobiense Ponomarenko, 1997

14. Cutting edge of mandible: (0) teeth horizontally arranged in longitudinal direction or only one apical tooth; (1) with vertically arranged teeth. The presence of three vertically arranged mandibular teeth is a characteristic feature of extant Ommatidae 7 12 and Micromalthidae 12 . The cutting edge is horizontal in Cupedidae as in most fossil ommatid beetles.

15. Pronotum: (0) narrowing anteriorly; (1) narrowing posteriorly. The pronotum is narrowing posteriorly in Pareuryomma (Figures 1A and 3A), but anteriorly in the other genera.

16. Surface convexities of the pronotum: (0) present; (1) absent. Only absent in Omma, Cionocoleus, and Odontomma 19 . Present in Cupedidae and other ommatids 3 6 .

17. Lateral pronotal projection (ventrally corresponding with pronotal epipleura): (0) as wide as or wider than one-fourth of the width of the main part of the pronotum; (1) narrower than one-fourth of the width of the main part of the pronotum. The paranota of Notocupoides, Rhabdocupes, Notocupes, Zygadenia, Eurydictyon, Amblomma, Cionocoleus, Pareuryomma, Brochocoleus, Odontomma, Lithocupes and Platycupes are widened 3 19 36 .

18. Procoxae: (0) separated; (1) adjacent. Adjacent in Ommatidae (Figure 4B). Distinctly divided in Cupedidae and Permocupes 3 .

19. Length ratio of the last to the penultimate abdominal ventrites: (0) less than 1.5 times; (1) more than 1.5 times. The last abdominal ventrite is longer than the penultimate one in Liassocupes, Notocupoides, Rhabdocupes, Zygadenia, Eurydictyon, Lithocupes and Amblomma 3 19 , and also in the cupedid genus Platycupes. It is even as long as the penultimate and antepenultimate ventrite in Tetraphalerus wagneri. (Hörnschemeyer T: Die phylogenic der Archostemata (Insecta: Coleoptera) und die evolution der flügelbasis der holometabolen insekten,unpublished.

20. Arrangement of abdominal sterna: (0) abutting, not overlapping; (1) posterior margin overlapping with anterior part of following ventrite. The posterior margin of the abdominal ventrites is overlapping with the anterior ones in Cupedidae and the genera Notocupoides, Rhabdocupes, Notocupes, Zygadenia, Eurydictyon and Amblomma 3 , whereas the ventrites are abutting in Brochocoleus, Odontomma, Pareuryomma, Omma, Cionocoleus and Tetraphalerus.

21. Length of mesofemur: (0) extending well beyond side margins of body; (1) not extending beyond side margins of body. The mesofemur of Omma, Cionocoleus, Brochocoleus, Odontomma, Notocupoides, Rhabdocupes, Notocupes, Zygadenia, Eurydictyon and Lithocupes is extending well beyond the lateral margin of the body, whereas it is short in the genera Tetraphalerus 2 , Amblomma and Pareuryomma.

22. Main elytral veins: (0) all longitudinal veins end on sutural margin before elytral apex; (1) only 2 sutural main veins meet before elytral apex. Two longitudinal main veins meeting before the elytral apex are present in Rhabdocupes, Notocupes, Zygadenia, Eurydictyon, Amblomma and Brochocoleus 3 19 .

23. Epipleural rim near basal part: (0) narrow, one row of cells; (1) more than one row of cells. More than one row of cells is present in the basal part of the epipleural rim of Pareuryomma, Odontomma and Brochocoleus 19 .

24. Elytra with cells (window punctures) on disk: (0) present; (1) absent. The cells are absent or very indistinct on the disk in Cionocoleus and Tetraphalerites, and the extinct species of Omma and Tetraphalerus 6 24 36 .

25. Size of window punctures: (0) enlarged, separated by very distinct rib-like ridges; (1) small. The window punctures of Eurydictyon, Notocupes, Notocupoides, Amblomma and Triadocupedinae are about 4 times as large as in the other taxa under consideration 3 and separated by conspicuous rib-like ridges 3 .

26. Regular row of large window punctures along external elytral margin: (0) present; (1) absent. A conspicuous regular row of large window punctures is present along the external elytral margin in Eurydictyon, Notocupes and Notocupoides, Amblomma, Lithocupes, Liassocupes, Pareuryomma, Odontomma and Brochocoleus, and also in Triadocupedinae 3 .

27. Pentagonal enlarged window punctures along elytral suture: (0) absent; (1) present. Pentagonal enlarged window punctures are present along the elytral suture in Eurydictyon and Notocupoides 3 .

(b)Parsimony analysis

The data matrix (see Additional file 1) used for the analysis contains 28 taxa (Table 1) and 28 morphological characters. All characters were equally weighted and non-additive. The matrix was modified in WinClada 37 and analyzed with NONA version 1.5 (options set to hold 10000 trees, perform 1000 replications with one starting tree replication, and the multiple TBR + TBR search strategy) 37 , and TNT (algorithm: traditional search; starting trees: Wagner trees, 100 replicates; swapping algorithm: tree bisection reconnection) 38 , respectively. Nodal support for the cladogram was assessed using Bremer support (BS) 39 40 values in TNT. Kirejtshuk et al. 41 proposed some synonyms within Ommatidae. Herein we conducted the topological constraints to determine the obscure interrelationships among Tetraphalerus + Odontomma and Pareuryomma + Notocupes using PAUP v4b10. Three topological constraints were imposed in cladistic analysis enforced the monophyly of Tetraphalerus + Odontomma and Pareuryomma + Notocupes respectively according to Kirejtshuk’s hypothesis.

The systematic position of the taxa is based on original descriptions. T₃ —Late Triassic; J₁—Early Jurassic; J₂—Middle Jurassic; J₃—Late Jurassic; K₁—Early Cretaceous; E₃-Oligocene; Fm.—Formation.

Order Coleoptera Linnaeus, 1758

Family Ommatidae Sharp et Muir, 1912

Subfamily Ommatinae Sharp et Muir, 1912

Tribe Ommatini Sharp et Muir, 1912

Genus Pareuryomma Tan, Ren, Shih et Ge, nom. nov.

Pareuryomma Tan, Ren, Shih et Ge, 2006 (nect. Stein, 1899) nom. nov.

Pareuryomma nom. nov., for Euryomma Tan, Ren, Shih et Ge 2006 (Coleoptera: Archostemata) nect. Stein, 1899 (Diptera: Fanniidae).

Kirejtshuk et al. 41 considered Pareuryomma as a synonym of Notocupes Ponomarenko, 1964. The new fossil specimens clearly show that this genus is distinctly different from Notocupes. Pareuryomma can be distinguished from Notocupes by the following characters: dorsal head surface without longitudinal bulge or keel; antennae moniliform, antennomeres 7–11 widened distally; pronotum widest anteriorly, narrowing posteriorly; abdominal ventrites arranged in one plane, not overlapping.

Head capsule: with distinctly protruding compound eyes approximately as wide as long; distinctly narrower anteriorly and posteriorly than at ocular region and temples; distinctly prognathous; without raised tubercles or longitudinal bulge or keel on dorsal surface; anterior margin very slightly convex; frontoclypeal suture not recognizable; temples short, about 0.3 times as long as eyes, moderately projecting laterally (Figure 3A). Compound eyes at middle region of head approximately round in outline, distinctly convex and protruding laterally; neck region moderately constricted, slightly shorter than compound eyes. Gula sub-rectangular, narrowing anteriorly; gular suture reaching posterior margin of head, widely separating genal regions on ventral side (Figure 3B).

Head appendages: labrum not recognizable. Antennae inserted laterally, at about midlength between anterior margin of head capsule and anterior margin of eyes; scape slightly wider than long; pedicel shorter than scape; flagellum not preserved. Mandibles short, with fairly broad proximal part and with one apical tooth (Figure 3A). Ventral mouthparts not recognizable.

Pronotum: subparallel, slightly narrowing posteriorly; distinctly wider than head; about 2/3 as long as wide at anterior edge; about 3/5 times as long as width at posterior edge; anterior pronotal edge moderately concave; posterior edge straight; anterolateral edge rounded, moderately produced; posterior angles rounded; lateral margins almost straight, very slightly curved; lateral longitudinal line separating lateral projection from slightly convex main part of pronotum distinct; lateral projection (paranotum) slightly widened; central disc with two flat elevations (Figure 3A).

Scutellar shield: exposed, shield-like, distinctly longer than wide; lateral margins concave, slightly widening anteriorly.

Elytra: both elytra together about 2 times as wide as maximum width of prothorax; maximum width at elytral midlength; individual elytron 3.2 times as long as wide; very strongly pronounced dorsolateral ridges and sharply pronounced lateral edge enclose flat or even slightly concave epipleural rim; elytral disc enclosed by dorsolateral ridges, also flat or slightly concave except for anteriormost part; epipleural rim widening in anterior half, lacking distinct cells, narrowing towards apex; dorsolateral ridges anteriorly connected with elytral shoulders; main veins of elytra similar to intermediate ones (Figure 3A); elytral cells (=window punctures) moderately distinct, small; regular rows of large cells along lateral elytral margin absent (Figure 3C); elytra reaching slightly beyond abdominal apex; appearing dehiscent in posterior third (possibly an artifact of compression during fossilization).

Thoracic venter: prothoracic notopleural suture straight and diverging posteriorly; anapleural cleft converging posteriorly towards procoxae; both sutures enclose triangular, anteriorly narrowing pleura, which meet the anterior prothoracic margin at a narrow point; prosternal process absent; protrochantin not recognizable. Individual structures of mesoventrite not recognizable. Metaventrite trapezoidal, distinctly narrowing anteriorly; posterior margin 1.8 times as wide as length at midline; anterior margin distinctly narrower than posterior margin, about as wide as mesocoxae combined; mesocoxae separated by short, rounded median process of metaventrite; metathoracic discrimen and metakatepisternal suture present; metatrochantin present and exposed between hind margin of katepisternum and coxa. Individual structures of metapleuron not recognizable; metanepisternum apparently broad anteriorly and narrowing towards end of segment (Figure 3B).

Legs: procoxae medially adjacent, medium-sized, cone-shaped but rounded apically; protrochanter small, slightly oblong; profemora short, widening distally, with strongly convex posterior margin, distinctly thicker than proximally curved and slender protibiae and slightly longer; mesocoxae slightly smaller than procoxae, nearly circular; mesotrochanter nearly oblong; mesofemora short, not reaching lateral margin of elytra; parallel-sided, thicker than mesotibia and about equally long; metacoxae transverse, distinctly reaching beyond lateral margin of metaventrite; triangular, without metacoxal plates; posteromesal apices rounded, far from posterior margin of first visible abdominal ventrite; metatrochanter small, nearly triangular; metafemur short, not extending beyond lateral margins of body, proximally distinctly thicker than distally; metatibia longer than metafemur; curved proximally, subparallel, widening very slightly distally.

Abdomen: with five visible ventrites; narrowing towards apex from the base of ventrite 3; first ventrite longer than other ones; last ventrite (=sternite VII) 1.5 times as long as the previous one; hind margin evenly rounded (Figure 3B).

Dimensions (mm): body length 7.5, width 2.8, head length 1.1, width 1.2, anterior edge of pronotum 2.0, posterior edge of pronotum 1.5, pronotal width 1.1, elytral length 5.3, width 1.4.

Head capsule: slightly shorter than maximum width at temples; upper surface more or less flattened, without raised tubercles or other prominent structures; anterior margin distinctly concave; frontoclypeal suture not recognizable (Figure 1A). Compound eyes at middle region of head largely integrated in the contour of the head, scarcely protruding laterally; neck region distinct narrow. Gula sub-rectangular; gular ridges reaching posterior margin of head, widely separating genal regions on ventral side (Figure 1B).

Head appendages: labrum not recognizable. Antennae inserted laterally; clavate, not reaching posterior margin of prothorax, distally widening; scape as long as last antennomere; pedicel wider than long, nearly as wide as scape; third antennomere not longer than second and fourth combined; antennomeres 7–10 short, distinctly broader than antennomeres 3–6; apical antennomere short and wide, appearing inflated. Labium with large submentum, slightly widening anteriorly, separated from gula by transverse suture; mentum not recognizable, apparently reduced; prementum large, plate-like; remaining elements of ventral mouthparts not visible (Figure 1A).

Pronotum: transverse, distinctly wider than head; widest at middle, slightly narrowing posteriorly; width at anterior margin about 1.5 times of length at midline; anterior pronotal edge along neck region almost straight, at most very slightly curved inwards, distinctly emarginated laterally, with rounded, moderately prominent anteriolateral edge; posterior angles completely rounded, not prominent; lateral longitudinal line separating lateral projection from slightly convex main part of pronotum moderately distinct; lateral pronotal projection (paranotum) distinctly widened; central disc bearing cordiform elevation (appearing as convexity in specimens with exposed ventral side) (Figure 1A).

Scutellar shield: exposed, triangular.

Elytra: disc flattened, only very slightly convex; both elytra together about 1.7 times as wide as maximum width of prothorax; individual elytron about 3 times as long as wide; maximum width at about midlength of elytra; pronounced dorsolateral ridges of elytra and sharply pronounced lateral edge enclosing flat or even slightly concave epipleural rim; elytral disc enclosed by dorsolateral ridges, also flat or slightly concave except for anterior-most part; dorsolateral ridges anteriorly connected with elytral shoulders; epipleural rim with two rows of cells in the proximal two thirds and one row in the distal third; main veins of elytra similar to intermediate ones; elytral cells (=window punctures) on disc small, indistinct; regular row of large cells along lateral margin absent; elytra reaching slightly beyond abdominal apex; appearing dehiscent in posterior third (possibly an artifact of fossilization) (Figure 1A).

Thoracic venter: prothoracic anapleural cleft converging posteriorly towards anterior procoxal margin; notopleural suture not visible; prosternal process absent. Mesoventrite with distinct discrimen; mesokatepisternal suture present as a distinct arched row of punctures. Metaventrite trapezoid, distinctly narrowing anteriorly; posterior margin 1.9 times as wide as length at midline; anterior margin slightly narrower than mesocoxae combined; mesocoxae separated by short, triangular, apically pointed process of metaventrite; metathoracic discrimen present but very short; metakatepisternal suture present; metatrochantins present and exposed between hind margin of katepisternum and coxa. Metanepisternum triangular, extensive, strongly widening anteriorly, and narrowing towards end of segment (Figure 1B).

Legs: procoxae nearly spherical, protruding, medially adjacent; protrochanter small, approximately triangular; profemora with convex anterior and posterior margins, distinctly widening in middle region, distinctly thicker than protibiae and slightly longer; protibia slender, slightly widening distally; two slender protarsomeres preserved; mesocoxae more conical, not protruding, posteriorly oriented, distinctly separated by mesokatepisternal region; mesotrochanter small, transverse; mesofemora with convex anterior and posterior margins, widening in middle region, distinctly thicker than mesotibia and slightly longer, not reaching beyond lateral margin of body; mesotibia subparallel, hind margin slightly convex; mesotarsus with 5 tarsomeres; tarsomeres 1 and 5 elongate, nearly equal in length; tarsomeres 2–4 distinctly shorter, only slightly longer than wide, nearly equal in length; metacoxae transverse, distinctly reaching beyond lateral margin of metaventrite; triangular, without metacoxal plates, posteromesal apices rounded, far from posterior margin of first visible abdominal ventrite; metatrochanter small, oblong; metafemur with very slightly convex anterior and posterior margin, short, not extending beyond lateral margin of body; metatibia very slightly widening distally, almost parallel-sided, shorter than metafemur; metatarsus 5-segmented; tarsomeres very similar to those of middle leg.

Abdomen: narrowing towards the apex from the base of ventrite 4; first abdominal ventrite longer than other ones, likely representing fused sternites II and III; last ventrite (=sternite VII) 1.35 times as long as previous one; hind margin evenly rounded.

Dimensions (mm): body length 6.6, width 2.5, head length 1.1, width 1.0, anterior edge of pronotum 1.5, posterior edge of pronotum 1.4, pronotal width 1.0, elytral length 4.5, width 1.4.

Genus Omma Newman, 1839

Omma Newman, 1839, Ann. Mag. Nat. Hist. 3:303; Peyerimhoff, 1902, Bull. Soc. Ent. Fr., p.330; Sharp and Muir, 1912, Trans. Ent. Soc. Lond., p. 521, 615, 632; Neboiss, 1959, Proc. Roy. Soc. Vic. 72:17; Crowson, 1962, Ann. Mag. Nat. Hist. 13(5): 147–157; Atkins, 1963, Can. Ent. 95: 140–162; Ponomarenko, 1964, Paleontol. Jour. 4: 45–55; Ponomarenko, 1966, Entomolog. Oboer. 1: 138–143; Ponomarenko, 1968 Nauka, Moscow. p. 118–138; Ponomarenko, 1969, Tru. Paleontol. Instit. A. N. SSSR, 125: 70–115; Ponomarenko, 1997, Paleontol. Jour. 31(4): 389–399; Lawrence, 1999, Inver. Taxon. 13:369–390; Ponomarenko, 2006, Paleontol. Jour. 40(1):90–99.

Omma delicata sp. nov. (Figure 1)

Head capsule: slightly longer than wide, but appearing elongated; distinctly narrower anteriorly than at ocular region; distinctly prognathous; without macroscopic tubercles on dorsal surface; anterior margin shallowly concave; temples distinctly shorter than eyes, moderately projecting laterally. Compound eyes posterior, approximately round in outline, distinctly convex and protruding laterally; neck region moderately constricted, with conspicuous postocular extensions (Figure 4A).

Head appendages: Antennae inserted laterally in front of eyes; filiform, thin, with 9 visible antennomeres; short, not reaching posterior margin of prothorax; scape subtriangular, longer than wide, wider apically than basally; pedicel thin, shorter than scape; antennomere 3 longer than others, nearly as long as pedicel and antennomere 4 combined; other antennomeres nearly equal in length, slightly widening distally; apical antennomere parallel-sided. Mandibles large, without recognizable teeth along horizontal mesal surface (Figure 4A). Remaining elements of ventral mouthparts not recognizable.

Pronotum: rounded at sides, widest posterior to midlength and not explanate, slightly wider than base of head; about 4/5 times as long as wide at anterior margin; posterior edge about as wide as pronotal length; anterior and posterior pronotal edges almost straight; central disc flattened, without elevation but with large tubercles (Figure 4A).

Scutellar shield: exposed, roughly triangular.

Elytra: maximum width at elytral midlength; individual elytron 3.7 times as long as wide; epipleural rim rather narrow; elytral disc enclosed by dorsolateral ridges, also flat or slightly concave except for anteriormost part; dorsolateral ridges anteriorly connected with elytral shoulders; elytra reaching slightly beyond abdominal apex; appearing dehiscent in posterior fourth (possibly an artifact of compression during the fossilization) (Figure 4A).

Thoracic venter: anapleural cleft converging posteriorly towards procoxae; prothoracic notopleural and sternopleural sutures enclose triangular, anteriorly narrowing pleura, which meet the notopleural suture at a narrow point; protrochantin not recognizable. Longitudinal suture (discrimen) present on mesoventrite. Metaventrite trapezoidal, distinctly narrowing anteriorly; posterior margin 2.1 times as wide as length at midline; anterior margin distinctly narrower than posterior margin, about as wide as mesocoxae combined; mesocoxae medially adjacent, separated by short, triangular, apically pointed process of metaventrite; metathoracic discrimen invisible; metakatepisternal suture present; metatrochantin present and exposed between hind margin of katepisternum and coxa (Figure 4B). Individual structures of metapleuron not recognizable; metanepisternum apparently broad anteriorly and narrowing towards end of segment.

Legs: procoxae nearly spherical, protruding, medially adjacent; protrochanter small, approximately triangular; profemur long, narrowing distally, with strongly convex posterior margin, distinctly thicker than protibia and slightly longer; protibia short, slender, slightly widening distally. Mesocoxae nearly triangular, larger than procoxae, medially adjacent; mesotrochanter small, longer than wide; mesofemora parallel-sided, with very distinct anterior and posterior margins, proximally wider than basally, distinctly thicker than mesotibia and equally long; mesotibia subparallel, with a short spur on the internal surface; mesotarsus with 4 visible tarsomeres; tarsomere 1 elongate, longer than others, tarsomeres 2–4 short. Metacoxae transverse, distinctly reaching beyond lateral margin of metaventrite, triangular, without metacoxal plates, posteromesal apices rounded, extending over mid-length of first visible abdominal ventrite; metatrochanter medium-sized, longer than wide; metafemora reaching beyond lateral margin of body; metatibia almost parallel-sided; metatarsi with 2 visible tarsomeres; tarsomere 1 elongate, longer than tarsomere 2.

Abdomen: narrowing towards apex from the base of ventrite 4; first ventrite longer than other ones; last ventrite (=sternite VII) 1.4 times as long as the previous one; apex rounded.

Dimensions (mm): body length 9.0, width 3.0, head length 1.5, width 1.6, anterior edge of pronotum 1.2, posterior edge of pronotum 1.7, pronotal width 1.5, elytral length 5.9, width 1.6.

Tribe Tetraphalerini Crowson, 1962

Genus Tetraphalerus Waterhouse, 1901

Tetraphalerus Waterhouse, 1901, Ann. Mag. Nat. Hist. Ser 7, Vol. Vii:520–523; Heller, 1913, Wien. Ent. Zeit. 32: 235; Bruch, 1925, Physis. 7: 201–204; Monrós and Monrós, 1952, An. Soc. Cient. Argent. 154: 23–39; Crowson, 1962, Ann. Mag. Nat. Hist. 13(5): 147–157; Atkins, 1963, Can. Ent. 95: 140–162; Ponomarenko, 1964, Paleontol. Jour. 4: 45–55; Ponomarenko, 1966, Entomolog. Oboer. 1: 138–143; Ponomarenko, 1969, Tru. Paleontol. Instit. A. N. SSSR, 125: 70–115; Lin, 1976, Acta Palaeontol. Sin. 15(1): 97–115; Ponomarenko, 1986, Trans. Joint Soviet-Mongolia Paleon. Exped. 28, 84–107; Ponomarenko, 1993, Tru. Paleontol. Instit. A. N. SSSR, 252: 17–20; Ren et al., 1995, Seism. Pub. H. pp77-78; Ponomarenko, 1997, Paleontol. Jour. 31(4): 389–399; Ponomarenko, 2000, Acta Geolog. Hispan. 35, n^o1-2: 47–52; Sorinao and Delclòs, 2006, Acta Palaeontol. Pol. 51(1): 185–200; Tan, Ren and Shih, 2007, Ann. Zoo. (Warszawa), 57(2): 231–247.

Head capsule: with distinctly protruding compound eyes at middle region of head approximately semicircular in outline, slightly wider than long; distinctly narrower anteriorly and posteriorly than at ocular region and temples; distinctly prognathous; anterior clypeal margin straight; frontoclypeal transverse line not recognizable; temples distinctly shorter than eyes, moderately projecting laterally. Ocelli absent. Two distinct circular, flat macro-tubercles present between posterior margins of eyes; median epicranial suture indistinctly visible; neck region distinctly constricted, as long as compound eyes (Figure 2A). Antennal groove on ventral side of head not visible.

Head appendages: Antennae inserted laterally in front of the eyes; moniliform, short, not reaching posterior margin of prothorax, wider apically than basally; scape approximately triangular, widening distally; pedicel small; antennomere 3 as long as pedicel and antennomere 4 combined. Mandibles exceptionally long and distinctly protruding; without recognizable tooth along horizontal mesal surface; outer margin curved; neck region moderately constricted, approximately as long as compound eyes (Figure 2A). Two maxillary palpomeres visible; remaining elements of ventral mouthparts not recognizable.

Pronotum: transverse, slightly wider than head; about 1.1 times as wide as anterior edge; about 1.3 times as wide as posterior edge; anterior and posterior margin almost straight; anterior and posterior angles of pronotum not prominent; lateral margin moderately serrate and moderately explanate; prothoracic hypomeron narrow; central disc near lateral pronotal carinae bearing two oblong flat convexities (Figure 2A).

Scutellar shield: exposed, shield-like, distinctly longer than wide; lateral margins concave, slightly widening anteriorly.

Elytra: individual elytron about 3.2 times as long as wide; pronounced dorsolateral ridges and sharply pronounced lateral edge enclose flat or even slightly concave epipleural rim; elytral disc enclosed by dorsolateral ridges, also flat or slightly concave except for anteriormost part; epipleural rim slightly widening in anterior 1/3, bearing one row of cells, narrowing towards apex; dorsolateral ridges anteriorly connected with elytral shoulders (Figure 2A); longitudinal ridges with small tubercles, with 9 rows of cells; elytral cells (=window punctures) moderately distinct, small, polygonal, with 4 black maculae on their margins; about 28 cells arranged in a row; regular rows of large cells along lateral elytral margin absent (Figure 2C); elytra reaching slightly beyond abdominal apex; appearing dehiscent in posterior third (possibly an artifact of compression during fossilization).

Thoracic venter: Individual structures of meso- and metaventrites not recognizable; metakatepisternal suture present; metatrochantins present and exposed between hind margin of katepisternum and coxa (Figure 2B).

Legs: procoxae medially adjacent, medium-sized, cone-shaped but rounded apically; protrochanter medium sized, longer than wide; profemur long, with strongly convex posterior margin; distinctly thicker than proximally curved and slender protibia and slightly longer; protibia short, slightly widening distally; protarsus 5-segmented; tarsomeres 2–4 short, only slightly wider than long; tarsomere 5 longer than others, with one claw; mesocoxae inconspicuous, slightly smaller than procoxae, apparently globular in outline, separated from each other; metacoxae transverse, triangular; without metacoxal plates; posteromesal apices rounded, far from posterior margin of first abdominal ventrite (Figure 2B).

Abdomen: narrowing towards apex from the base of ventrite 3; hind margin evenly rounded (Figure 2B).

Dimensions (mm): body length 8.7, width 3.1, head length 1.6, width 1.4, anterior edge of pronotum 1.6, posterior edge of pronotum 2.0, pronotal width 1.5, elytral length 5.5, width 1.7.

(a) Tree for fossil and extant Ommatidae

Nine most maximum parsimonious trees were obtained in the NONA analysis (tree length = 57 steps, CI = 0.50, RI = 0.80). A similar result was obtained in analyses using TNT (9 trees, 57 steps). The strict consensus tree obtained with NONA with Bremer support values mapped on branches is shown in Figure 6. The cladistic result obtained by TNT is similar to the results by NONA (see Additional file 2). The constrained analysis forcing the monophyly of Tetraphalerus + Odontomma and Pareuryomma + Notocupes yielded 434 most-parsimonious trees (tree length = 67 steps, CI = 0.42, RI = 0.76; see Additional file 3: Figure S1B), with 10 additional steps compared to the unconstrained results. The constrained analysis forcing the monophyly of Tetraphalerus and Odontomma yielded 972 most-parsimonious trees (tree length = 61 steps, CI = 0.48, RI = 0.80; see Additional file 3: Figure S1C). The constrained analysis forcing the monophyly of Pareuryomma + Notocupes yielded 140 most-parsimonious trees (tree length = 63 steps, CI = 0.46, RI = 0.79; see Additional file 3: Figure S1D)

The constrained analysis forcing the monophyly of Tetraphalerus + Odontomma and Pareuryomma + Notocupes yielded 434 most-parsimonious trees (tree length = 67 steps, CI = 0.42, RI = 0.76; see Additional file 3: Figure S1), which need nine additional steps more than the most parsimonious results. The constrained analysis forcing the monophyly of Tetraphalerus and Odontomma yielded 972 most-parsimonious trees (tree length = 61 steps, CI = 0.48, RI = 0.80; see Additional file 3: Figure S1). The constrained analysis forcing the monophyly of Pareuryomma + Notocupes yielded 140 most-parsimonious trees (tree length = 63 steps, CI = 0.46, RI = 0.79; see Additional file 3: Figure S1).

(b) Apomorphies of selected clades

The monophyly of Ommatidae is supported by two apomorphic characters: the antenna not reaching hind margin of prothorax posteriorly (ch. 9), and the medially adjacent procoxae (ch. 18). In all trees, Notocupoides and Eurydictyon are a monophyletic group (sharing ch. 27) and form the sister group of all other included ommatid taxa. Ommatidae excl. Notocupoides + Eurydictyon is supported by a ratio labral width/clypeal width less than 1 (ch. 7:1).

Ommatidae excluding the traditional tribe Notocupedini (including the genera Notocupoides, Eurydictyon, Notocupes, Amblomma, Rhabdocupes, and Zygadenia) are monophyletic. This clade is supported by the absence of a longitudinal bulge or keel on the dorsal head surface (ch. 0:1), the distinct elongation of the third antennomere (ch. 11:1), and the small size of the window punctures on the elytron (ch. 25:1).

A clade including the genera Brochocoleus, Odontomma, Pareuryomma, Liassocupes, Omma, Cionocoleus, Tetraphalerus and Tetraphalerites is suggested by abutting abdominal sterna (ch. 20:0). However, this condition is arguably plesiomorphic. Lithocupes, the only single genus of the tribe Lithocupedini, is placed as the sister taxon of this clade in all trees, shared derived features are the above mentioned apomorphies of Ommatidae excl. the traditional Notocupedini.

The three genera Brochocoleus, Odontomma and Pareuryomma constitute a clade defined by one non-homoplasious character, an epipleural rim containing more than one row of cells near its basal part (ch. 23:1), and one homoplasious character, the absence of the posteromesal dorsal protuberance of the head (ch. 1:1). Liassocupes, Omma and Cionocoleus are supported as a clade by the absence of the median epicranial (=coronal) suture on the dorsal head (ch. 2:1). The two genera, Tetraphalerus and Tetraphalerites share a non-homoplasious apomorphic character state, the presence of ventrolateral antennal grooves (ch. 3:1). However, this ventral groove is not visible in the fossils of Tetraphalerus. There are several homoplasious characters also supporting this group, such as a strongly transverse labrum (as wide as the clypeus) (ch. 7:0) and a mesofemur not extending beyond side margins of body (ch. 21:1). The two lineages are likely sister taxa, as suggested by the non-homoplasious absence of the frontoclypeal suture (ch. 6:1), which reduced countless times in Coleoptera, and the narrower lateral pronotal projection (ventrally corresponding with pronotal epipleura) (ch. 17:1).

The interrelationships within the family Ommatidae are still uncertain. Conventionally, Ommatidae is divided into four subfamilies: Lithocupedinae, Notocupedinae, Ommatinae and Tetraphalerinae 7 . Herein, we conducted a cladistic analysis to infer the phylogenetic relationships of the extinct and extant genera within the family. Although the generic relationships are still not well resolved, the results of the phylogenetic analysis suggest six monophyletic groups: Pronotocupedini, Notocupedini, Lithocupedini, Brochocoleini, Ommatini and Tetraphalerini. Only the two subfamilies Lithocupedinae and Tetraphalerinae were recovered, while the other two, Notocupedinae and Ommatinae, turned out as paraphyletic. Therefore, we propose to use these six tribes to replace the traditional four subfamilies 7 in presenting the higher-level relationships within Ommatidae.

The paraphyly of the traditional of Notocupedinae 7 , including Notocupoides, Eurydictyon, Rhabdocupes, Zygadenia (Notocupes), and Amblomma, implies a reassessment of taxa previously assigned to this subfamily. The monophyletic tribe Notocupedini apparently includes only Rhabdocupes, Zygadenia (Notocupes), and Amblomma. The placement of the Lower Triassic genera Notocupoides and Eurydictyon as the sister group of the remaining Ommatidae is tentatively supported in the parsimony analysis. Thus, these two genera cannot be included in the tribe Notocupedini. These two ancestral genera, the earliest representatives of Ommatidae in the fossil record, are assigned to a new tribe Pronotocupedini, as the sister group of all other ommatids.

Ponomarenko 23 considered Notocupes Ponomarenko, 1964 as a junior subjective synonym of Zygadenia Handlirsch, 1909. However, in a more recent study 24 25 , he pointed out that the Notocupes was described based on the study of more or less complete bodies of the beetle, while the genus Zygadenia was proposed only based on the elytra. Therefore, Ponomarenko 24 concluded that the synonymy of Notocupes under Zygadenia would impede the placement of the genus, and Zygadenia should be regarded as an informal morphogenus. The results of the present analyses, as shown in Figure 6, also support this view.

The relationships of the genera Amblomma, Notocupes and Rhabdocupes are still unclear. These genera are characterized by a peculiar venation of their elytra with double rows of cells between the veins and only 2 sutural main veins meeting before elytral apex. Notocupes, which was the most common and diverse genus among Mesozoic ommatids, is recorded from the Early Triassic to the Early Paleocene 3 20 23 24 . Except for the difference in the proportions between the pedicel and third antennomere, the species of the Early Cretaceous genus Amblomma and the Early Triassic genus Rhabdocupes could be members of Notocupes Ponomarenko, 1964 16 . However, this requires a careful re-examination of specimens assigned to these genera.

The subfamily Ommatinae turned out as a paraphyletic assemblage, and was divided into two separate monophyletic groups, Brochocoleini and Ommatini in our analyses. Three genera Brochocoleus, Odontomma, and Pareuryomma were attributed to the tribe Brochocoleini. This tribe was first described by Hong 43 as a new archostematan family Brochocoleidae. After Hong’s work, Ponomarenko 44 also found some complete ommatid beetles with wide elytral epipleural rims with several rows of cells from the Jurassic of Mongolia. However, after studying these fossils, Ponomarenko concluded that the placement of Brochocoleidae was unjustified, as it was based on a single elytral fossil. He proposed a status as a tribe Brochocoleini within Ommatinae. In our analysis, Brochocoleini is the sister group of Tetraphalerini and Ommatini. A presumably synapomorphic feature of the tribe is the presence of more than one row of cells near the basal part of the elytral epipleural rim (see above). Based on this feature 22 , Brochocoleus aphaleratus (Ponomarenko 1969) 3 was transferred from the genus Tetraphalerus to Brochocoleus by Ponomarenko in 1997.

The genus Odontomma was erected by Tan, Ren et Ge, 2006 which is characterized by a flattened dorsal head surface and a wider epipleural rim. Kirejtshuk et al. 41 considered it should be a synonym of Tetraphalerus Waterhouse, 1901. In our cladistic analysis, Odontomma was assembled to Brochocoleini instead of showing close relation to Tetraphalerus. In the topological constraint analysis, enforcing the monophyly of Tetraphalerus + Odontomma gained more steps than the unconstrained analysis, implying Odontomma should be a valid genus.

The other genus Pareuryomma was assigned to Brochocoleini, which is incompatible with Kirejtshuk’s assumption as a synonym of the genus Notocupes (Zygadenia) Ponomarenko, 1964 41 . The constrained analysis forcing the monophyly of Pareuryomma and Notocupes gained four additional steps comparing with the unconstrained results. In fact, Pareuryomma differs from the Notocupes (Zygadenia) in several characters: the absence of protuberances or longitudinal bulges or keels on the dorsal surface of the head, moniliform antennae, a quadrate pedicellum, a wide epipleural rim, and the abutting arrangement of the abdominal sterna. Therefore, we consider the arrangement of Pareuryomma within Brochocoleini is more suitable.

Three genera Liassocupes, Cionocoleus and Omma are placed in a subgroup of the tribe Ommatini, which is supported by the following characters: the absence of the median epicranial suture on the head, the absence of the elevation on the pronotal disc, and a propleuron indistinctly fused to the sternum.

The monophyly of Tetraphalerini was weakly supported in our analyses by one character not identifiable in fossils. The systematic position of the genus Tetraphalerites Crowson, 1962 remains rather unclear. This genus includes only one species, Tetraphalerites oligocenicus Crowson, 1962. Ponomarenko transferred Tetraphalerites to the tribe Brochocoleini in 2006 24 . The visible ventral structure (including the impressions of middle and hind femora) are very similar like that to recent Tetraphalerus 2 , but the elyra are not quite like those of this genus. Because of the poor preservation of the specimens with many characters not recognizable (e.g., antennal groove), we tentatively attributed Tetraphalerites to Tetraphalerini based on a single recognizable apomorphy, which is a mesofemur not extending beyond side margins of body.

The recent phylogenetic results shed light on the evolutionary trends of key characters (Table 2) and evolutionary processes.

Pentagonal enlarged window punctures along the elytral suture is an unusual autapomorphy of the tribe Pronotocupedini. The species of Notocupedini have the 3^rd and 4^th antennomeres equal in length, the gula not converging posteriorly, and the size of window punctures enlarged and separated by very distinct rib-like ridges. The gula of Lithocupedini is similar to that of Notocupedini, but the third antennomere is longer than the fourth one, the rows of punctures are of normal size. The epipleural space of the elytron in Brochocoleini is very wide with more than one row of proximal cells. Except for this archostematan tribe, only two families have a wide epipleural margin with several rows of cells: Tshekardocoleidae in the Permian and Labradorocoleidae in the Early Cretaceous. After the Permian, the wide epipleural rim apparently evolved for a second time in Brochocoleini and then another time in Labradorocoleidae in the Cretaceous. Ommatini have gular sutures that are incomplete, not reaching the hind margin of the head capsule, and the median epicranial suture on the dorsal head surface is absent. Moreover, the gular sutures in Tetraphalerini species are absent. Lateral antennal grooves are present on the ventral side of the head in species of Tetraphalerini, which is an autapomorphy of this group.

The species of the tribe Pronotocupedini is consistent with the early appearance of the group in the ommatid fossil record. The evolutionary innovation linked with the earliest splitting event in the Lower Permian is a shortening of the elytra, which then fit better with the shape of the abdomen 12 , distinct modifications of the elytral venation 45 , and a distinctly narrowed prosternal process 45 . The tribe Notocupedini was present from the Early Triassic of Kyrgyzstan to the Early Cretaceous of Russia and Spain 3 . The tribe Lithocupedini was represented in Central Asia from the Early Triassic to the Early Jurassic. The more advanced Ommatini appeared in the Lastest Triassic 2 3 and became abundant in Europe and Asia during the Mesozoic. However, only four extant species of Omma occur in Austrialia today. The new fossil species of Omma described here is the first Chinese representative of this genus, thus, extends its geographical distribution from Central to Eastern Asia. The earliest occurrence of Tetraphalerini is in the Lower Jurassic of Kyrgyzstan 3 . Today only two species of Tetraphalerus have been reported from South America 6 8 . The phylogenetic relationships of the genera of Ommatidae are summarized in Figure 7.