New fossil species of ommatids (Coleoptera: Archostemata) from the Middle Mesozoic of China illuminating the phylogeny of Ommatidae

Background Ommatidae is arguably the “most ancestral” extant beetle family. Recent species of this group are only found in South America and Australia, but the fossil record reveals a much broader geographical distribution in the Mesozoic. Up to now, thirteen fossil genera with more than 100 species of ommatids have been described. However, the systematic relationships of the extant and extinct Ommatidae have remained obscure. Three constraint topologies were designed based on Kirejtshuk’s hypothesis, enforced the monophyly of Tetraphalerus + Odontomma, Pareuryomma + Notocupes and both respectively. Results In this study, four new species, Pareuryomma ancistrodonta sp. nov., Pareuryomma cardiobasis sp. nov., Omma delicata sp. nov., and Tetraphalerus decorosus sp. nov., are described. Based on well-preserved fossil specimens and previously published data the phylogenetic relationships of extant and extinct lineages of Ommatidae were analyzed for the first time cladistically. Based on the results we propose a new classification with six tribes of Ommatidae: Pronotocupedini, Notocupedini, Lithocupedini, Brochocoleini, Ommatini and Tetraphalerini. These taxa replace the traditional four subfamilies. Conclusion There is good support for the monophyly of the ingroup. Notocupedini, as defined by Ponomarenko, are paraphyletic. Notocupoides + Eurydictyon are the sister group of the remaining fossil and extant ommatids. Together they form the clade Pronotocupedini. Notocupedini and Lithocupedini are the next two branches. The tribe Brochocoleini is the sister group of a clade comprising Tetraphalerini and Ommatini.


Background
Ommatidae is one of 4 or 5 extant beetle families of the suborder Archostemata [1]. The phylogenetic position of the family has been the subject of much controversy [2][3][4][5][6][7][8]. Based on differences of the aedeagus of Omma stanleyi Newman, 1839 [9] and Tenomerga mucida (Chevrolat, 1829), Ommatidae was first proposed by Sharp and Muir [8]. Crowson [2] placed the two recent ommatid genera in separate tribes, Ommatini and Tetraphalerini, and in 1976, he elevated both to family level [4,5]. In 1995, Lawrence and Newton [10] found the enclosure of sensilla in a deep sensorial cavity on the apical maxillary palpomere as an additional character uniting Omma and Tetraphalerus. This cavity is absent in Cupedidae. Based on this observation, Lawrence [7] discussed the relationships of the two genera to Cupedidae. He suggested to elevate Ommatinae to Ommatidae and described the features of this family. To date, a systematic position of Ommatidae within Archostemata is generally accepted [11][12][13][14].
Ommatidae is one of the "most ancestral" extant beetle families and a very small group. It includes the two extant genera, Omma Newman, 1839 [9] and Tetraphalerus Waterhouse, 1901 [15], with a total of six extant species. Their distribution is restricted to subtropical and more or less arid regions of the southern hemisphere. In contrast to the very limited range of the genera today, the recorded distribution in the Mesozoic was much broader. In addition to well preserved ommatid fossils in Mesozoic Lagerstätten of the eastern part of Russia and central Asia [3,[16][17][18], interesting and important fossils of the group were discovered not only at fossil sites in northeastern China [19], but also at sites in Spain [20] and other localities [2,21]. Up to now, thirteen fossil genera with more than 100 species of ommatids have been described [2,3,[16][17][18][19][20][21][22][23][24][25][26]. However, their systematic position within Ommatidae remained obscure.
Recently we collected several well-preserved fossils from the Jiulongshan Formation of Inner Mongolia and the 'Jianshangou Bed' in the lower part of the Yixian Formation of western Liaoning Province, China, respectively. Based on these material, four new species, Pareuryomma ancistrodonta sp. nov., P. cardiobasis sp. nov., Omma delicata sp. nov., and Tetraphalerus decorosus sp. nov., are described herein. O. delicata sp. nov. is the first fossil record of the genus Omma in China. These attractive fossils provide a very good opportunity to study morphological transformations within the family, such as changes of body size and modifications of the antennae, prothorax and elytra, and induced us to carry out the phylogenetic investigation of extant and extinct groups of this ancestral group of beetles. The morphological data obtained from the new specimens in combination with characters of other groups of Ommatidae and other archostematan taxa were used in a formal character evaluation. It is the first phylogenetic analysis of extant and extinct lineages of Ommatidae. Our study of these new ommatid species and the phylogenetic results provide a new understanding of the origin and evolution of Ommatidae. They also enable us to update the phylogenetic relationships of the genera of Ommatidae and to present a new classification for the group.

Methods
All specimens were collected from a fossil locality near Daohugou Village, Shantou Township, Ningcheng County, Inner Mongolia, China and the 'Jianshangou Bed' in the lower part of the Yixian Formation of western Liaoning Province, China, respectively. The age of the Daohugou beds was confirmed as the Middle Jurassic by extensive evidence [27]. Recent studies have confirmed the age of the Yixian Formation as Early Cretaceous. The precise age is most likely restricted to 129.7-122.1 Ma (Barremian to Early Aptian) [28,29].
This study is based on several specimens housed in the Key Lab of Insect Evolution & Environmental Changes, the College of Life Sciences, Capital Normal University, Beijing, China (CNUB; Dong Ren, Curator).
The specimens were examined with a LEICA MZ12.5 dissecting microscope and illustrated with the aid of a drawing tube attached to it. The inking was performed with Adobe illustrator CS5 graphics software. Photographs were taken using a Nikon D300s digital camera connected to a ZEISS Discovery V12 dissecting microscope, and processed using Adobe Photoshop. The systematic arrangement used here mainly follows Lawrence [7]. The body length was measured from the anterior clypeal margin to the apex of the abdomen. The body width was measured at the base of the elytra. The length of the elytra was measured from the horizontal anterior margin of the base to the apex.
To comply with regulations of the International Code of Zoological Nomenclature (ICZN), we have deposited paper copies of the above article at the Natural History Museum, London; the American Museum of Natural History, New York; the Muséum National d'Histoire Naturelle, Paris; the Russian Academy of Sciences, Moscow; and the Academia Sinica, Taipei.
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.  [42]. Consequently, the beetle genus Euryomma became the homonymy of Euryomma of the family Fanniidae. Based on the "International Code of Zoological Nomenclature (fourth edition)", we amend the genus name from "Euryomma" to "Pareuryomma". 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.

Description of the specimens
Pareuryomma ancistrodonta sp. nov.
Diagnosis Mandible with one apical tooth; temples shorter than eyes; anterior edge of pronotum distinctly curved inwards; anterolateral edge of pronotum rounded; central disc with 2 flat elevations.
Type material Holotype: a well-preserved adult with body, elytra, and parts of legs and antennae. Registration Description Body small, surface densely covered with tubercles ( Figure 5A). 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).
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).
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 Comments Pareuryomma ancistrodonta sp. nov. clearly belongs to the genus Pareuryomma indicated by the following characteristics: pronotum widest anteriorly, narrowing posteriorly; epipleural space of elytron wide with 2 rows of cells in the proximal half and narrowing towards the apex. The new species differs from the type species P. tylodes in several features: temples shorter than the eyes, anterior pronotal angle rounded. It can distinguish from P. cardiobasis sp. nov. in the specific shape of the mandibles with a single apical tooth.
Diagnosis Mandibles stout, with a distinctly dilated and tridentate apical part; temples conspicuously projecting laterally, about as long as eyes; anterior margin of pronotum as long as posterior margin; pronotal hypomeron wide; central disc with cordiform elevation.
Etymology Name derived from the Greek word 'cardiobasis' , -is, -e, (heart-shaped), referring to the central disc of the pronotum with a large cordiform elevation. Description Body small, flattened, densely covered with large tubercles ( Figure 5B). 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).

Type material
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 parallelsided, 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. Comments Pareuryomma cardiobasis sp. nov. differs from the type species in the following features: anterior margin of pronotum as long as the posterior margin, central pronotal disc bearing a cordiform elevation; from P. ancistrodonta in the presence of tridentate with perpendicular cutting edge of the mandible.
Emended diagnosis Body elongate, moderately flattened or almost cylindrical. Surface often tuberculate or rarely spinose. Head subquadrate to slightly elongate, always with distinct neck region; temples usually shorter than eye; antennal grooves absent. Antennae inserted laterally. Antennae filiform or somewhat moniliform, as long as or slightly shorter than head and prothorax together; antennomere 3 longest, as long as or longer than pedicel and antennomere 4 combined. Mandibles prominent, incurved. Labrum, clypeus, and frons fused. Pronotum subquadrate or slightly transverse, without lateral pronotal carinae; procoxal cavities contiguous. Legs moderately long and slender; tibiae usually not much longer than femora; mesofemora extending beyond side margins of body. Abdominal sternites arranged in one plane.
Note The emended diagnosis is based on the type species and the new material.
Omma delicata sp. nov. (Figure 1) Diagnosis Body small; head distinctly wider posteriorly behind compound eyes. Scape subtriangular, 1.2 times longer than pedicel, thicker than other antennomeres. Pronotum square, anterior and posterior angles of pronotum completely rounded, not prominent. Elytra with indistinct veins and cells; elytra 1.8 times as wide as prothorax.
Etymology Name derived from the Latin word 'delicatus' , -a, -um (delicate), referring to the relatively small size of the new species. Description Body small, flattened, densely covered with tubercles ( Figure 5C). 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 parallelsided. 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.
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. Included species 25 species have been known before this study. T. wagneri Waterhouse, 1901 and T. bruchi Heller, 1913 are two extant species from South America. The others are all fossil species from the Mesozoic of Siberia, Central Asia, Western Europe, Western Australia and China. In addition, T. decorosus sp. nov. is described below.
Emended diagnosis Head narrow anteriorly and broad in post-ocular region, with ridges and lobes. Antennae filiform or somewhat moniliform, as long as or slightly shorter than head and prothorax taken together; longitudinal, distinct antennal groove present on ventral side of head; antennomere 3 slightly long than antennomere 4. Clypeus and frons fused; labrum short, transverse. Mandibles prominent, incurved; temples as long as or longer than eyes. Pronotum nearly rectangular, as wide as head or narrower, with lateral longitudinal line; central part of pronotum strongly raised; procoxal cavities contiguous. Elytra 1.5 times to twice as wide as prothorax. Legs short, mesofemora not extending well beyond side margins of body; tarsal segment 4 simple.
Abdominal sternites arranged in one plane, abutting, not overlapping.
Note The emended diagnosis is based on the type species and the new material.
Diagnosis Head slightly longer than wide; antennae moniliform; antennomeres 5-10 short, distinctly broader than antennomeres 3-4, distally widening; apical antennomere appearing inflated. Maximum width of elytra posterior to midlength; abdominal ventrites narrowing towards apex from the base of ventrite 3; first abdominal ventrite longer than the other ones; last ventrite (=sternite VII) 1.3 times as long as the previous one; hind margin evenly rounded.
Etymology Name derived from the Latin word 'decorosus' , -a, -um, referring to the new species preserved completely. Description Body small, surface densely covered with large tubercles ( Figure 5D). 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.

Type Material
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).
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).
Comments The new fossil specimen is assigned to Tetraphalerus based on the following suite of characters: head nearly as wide as pronotum, antennae short, third antennomere longer than fourth, and the pronotum with lateral pronotal carinae. The presence of two prominences on the vertex suggests a placement of the new species to the T. bruchi series. The new species is distinctly different from other species in several features: head wider than long; antennae moniliform.

(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 mostparsimonious 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 mostparsimonious 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 nonhomoplasious 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 nonhomoplasious 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). Figure 6 Results of the phylogenetic analyses as represented by strict consensus tree by NONA. Black circles indicate non-homoplasious changes; white circles indicate homoplasious characters; numbers above the branches of the strict consensus tree indicate character numbers; Bremer support values presented above the branches. 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.

(b) Evolutionary trends and origin of Ommatidae
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.