An extraordinary palaeontinid from the Triassic of Korea and its significance

A new, extraordinary palaeontinid Hallakkungis amisanus Nam, Wang & Szwedo, gen. et sp. nov., from the Upper Triassic of the Amisan Formation in Boryeong City, Korea is described. It is the first Palaeontinidae from Korea. The newly described taxon displays a mosaic of characters present in presumed ancestors of this insect family and some highly advanced features.

Scientific RepoRts | 7:40691 | DOI: 10.1038/srep40691 The type material is deposited in the Department of Earth Science Education, Kongju National University, Korea. The wing venation nomenclature of Palaeontinidae used in this paper is based on the interpretations by Wang B. et al. 14 and Nel et al. 15  Diagnosis: Tegmen with costal margin strongly curved at base. Stem of subcosta posterior (ScP) with several branches intersecting costal area and costal cell, basal portion of ScP shifted from common stem radius + media posterior + cubitus anterior (R + MP + CuA) in distance exceeding the length of basal cell. Stem MP bifurcated into branches MP 1+2 and MP 3+4 earlier than stem ScP + R forking. Stem of CuA straight; branch CuA 2 strongly curved mediad in median ⅓ of its length. Crossvein r-mp 1 apicad of crossvein mp 3+4 -cua; crossvein mp 3+4 -cua connected with stem CuA before CuA forking; crossvein mp 3+4 -cua forms part of nodal line; apex of clavus obtuse, due to strong curving of the utmost distal part of cubitus posterior (CuP) claval veins postcubitus (Pcu) and analis prima (A 1 ) fused for a short distance as common stalk.
Remarks: Based on some venational characters, e.g. anterior margin indented, costa posterior (CP) present and ScP with several branches, this new genus is similar to Fletcheriana Evans, 1956, which was reported   Riek, 1976, from the Triassic of South Africa 17 was placed in the family Palaeontinidae. Later, the genus was discussed and some Jurassic species previously ascribed to this genus, were transferred to the other Palaeontinidae genera 14 . The genus Asiocossus Becker-Migdisova, 1962 from Kirghizstan 18 is incompletely preserved (only basal portion of forewing), and the deposit was reevaluated as early Jurassic.
The new genus described above clearly differs from 'Fletcheriana' magna by the very strong curving of costal margin at base, distinct shift of basal part of ScP from common stem R + MP + CuA for a distance exceeding the length of basal cell (this portion is not clear in 'Fletcheriana' magna); stem MP forked anteriad of stem ScP + R forking (similar pattern, but less anteriad in 'Fletcheriana' magna); straight stem CuA (strongly curved in 'Fletcheriana' magna); distinct mediad curving of median portion of CuA 2 branch (terminal CuA 2 almost straight in 'Fletcheriana' magna); veinlet mp 3+4 -cua composed to nodal flexion line (only part close to CuA 2 of mp 4 -cua composed to nodal flexion line in 'Fletcheriana' magna; this veinlet meets terminal MP 4 in 'Fletcheriana' magna not the branch MP 3+4 ); mp 3+4 -cua fused to stem CuA basad of CuA forking (connected with CuA 1 slightly apicad of forking in 'Fletcheriana' magna); discal cell about three times as long as wide and narrow (discal cell about twice as wide as long in 'Fletcheriana' magna).
Etymology: The generic name is derived from "Hallakkungi" -the Flower Warden God in the Soch' on Flower Garden, from the Korean mythology. Gender: masculine, 3 rd declension.
Hallakkungis amisanus Nam, Wang & Szwedo, sp. nov. (Fig. 2a,b). Diagnosis: Forewing elongately triangular, costal margin blade-like, distinct ambient vein and narrow appendix present; corrugations exceeding to narrow appendix and apical portions of apical cells. Stem CP faint, costal area widest at base, with intersecting branchings of ScP more distinct. Stem ScP emitting six braches intersecting costal area and costal cell, these branches dispersed in increasing distance each other. Veinlet mp 3-4 -cua long, slightly sigmoid, connecting branch MP 3+4 just after its separation from stem MP to stem CuA at ½ of stem CuA length. Discal cell elongately almond-shaped, with acute apical angle, about 3 times as long as broad at widest point.
Etymology: The specific epithet is derived from the Amisan Formation, in which the fossil has been found.  straight. Apex of clavus not reaching ⅓ of total length of forewing. Posteroapical margin corrugated, corrugations on appendix and at basal portions of apical cells. Costal margin (costa anterior; CA) strongly curved at base, blade-like, arcuate to nodal incision, arcuate apicad of nodal incision towards the anteroapical angle. Vein CP obscure, slightly curved and ending at the level of nodal indentation. Stem ScP distinctly separated from common stem R + MP + CuA at base, fused with stem R distinctly apicad of basal cell apex. Costal area and costal cell intersected by six branchings of ScP, with spaces between branchings sequentially increasing; apical portions of these branchings more distinct on costal area. Stem R + MP + CuA thick, stems R, MP and CuA leaving basal cell separately. Stem R strongly curved anteriad at base, forked basad of nodal line incision, slightly posteriad of stem MP forking; branch RA forked basad of nodal line incision, terminal ScP short, branch RA 1 reaching anterior forewing margin at about half of post-incision portion length, branch RA 2 longer, reaching anterior margin distinctly basad of anteroapical angle. Stem MP curved at base, forked basad of stem R forking, apicad of stem CuA forking; branch MP 1+2 shorter than branch MP 3+4 ; forking of branch MP 1+2 merely apicad of nodal incision level, slightly earlier than forking of MP 3+4 ; forking MP 3+4 more apicad than nodal incision; terminals MP 1 , MP 2 , MP 3 and MP 4 slightly curved, reaching margin in median portion of posteroapical margin of forewing. Stem CuA leaving basal cell thick, straight, forked at basal ¼ of forewing length, basad of claval apex; branch CuA 1 curved anteriad, reaching the posteroapical margin before posteroapical angle; branch CuA 2 straight at basal ⅓, then strongly curved mediad, apical ⅓ thinner, slightly wavy, reaching posterior margin beside the posteroapical angle. Claval vein CuP thicker at base, thinner in apical portion, distinctly curved posteriad at claval apex, forming obtuse claval apex. Claval veins Pcu and A 1 fused in apical ¼ of clavus. Posteroclaval margin distinct, not strongly separated from postclaval margin. Crossvein r-mp 1 short, distinctly apical of nodal line; crossveins mp 3+4 -cua long, sigmoid, included to nodal (flexion) line, connecting branch MP 3+4 slightly after stem MP forking with stem CuA at half of its length after separation from basal cell. Nodal line distinct, from nodal line incision at anterior margin, through terminal ScP, stem R forking, cutting branches MP 1+2 and MP 3+4 slightly after the stem MP forking, then, followed with crossvein mp 3+4 -cua for a long interval and after separating from mp 3+4 -cua crossvein, fused with basal ⅓ of branch CuA 2 finally, separating from CuA 2 and reaching CuP at level of claval apex.

Discussion
Hallakkungis amisanus gen. et sp. nov. is the first palaeontinid described from the Korea. Regarding its strongly triangular shape of the forewing, the new taxon resembles more the Early Cretaceous representatives of the family 19 . The more triangular shape of the forewing is an important character of the Palaeontinidae from the Late Jurassic to the Early Cretaceous [20][21][22] , but the venation pattern is clearly different. In the Jurassic and Cretaceous Palaeontinidae with triangular wings the hind wing is usually diminished due to particular kind of flight, discussed in ref. 23, but the question of a similar tendency in Hallakungis gen. nov. hind wings and flight performance remains open. The new genus Hallakkungis gen. nov. presents number of unique features, some of them shared also with presumed ancestors of Palaeontinidae, i.e. representatives of the family Dunstaniidae 14 . The strong curve of the costal margin at the base is one of peculiar features of the newly described genus. Such trend in forewing shape is observed in Dunstaniidae (e.g. Fletcheriana triassica), also in not related to Palaeontinoidea representatives of superfamily Pereborioidea -families Perboriidae and Ignotalidae 24,25 . The very late separation of RA and RP only just before the node, is similar to the situation in the Permian Prosbolidae. Such a late separation is common in Triassic palaeontinoids, and it is probably a plesiomorphic condition, but in Hallakungis gen. nov., it is unusually late. Another feature worth of mention is the basal separation of the ScP -such situation is present in majority of Jurassic Palaeontinidae, much less common in Dunstaniidae. The feature resembling the situation common with Dunstaniidae is the connection of crossvein mp 3+4 -cua to the stem CuA. In the vast majority of Palaeontinidae it is connected near, at the point or the distad of point of forking of stem CuA, while in Hallakkungis gen. nov. this point is distinctly more basal, at half of the common stem CuA length. In the other Palaeontinidae, this crossvein meets the terminal MP 4 , while in Hallakungis gen. nov., it is placed more basad, and meeting the branch MP 3+4 in proximity of stem M forking, which is unusual. The exceptional feature of the newly described genus Hallakkungis is that the vast portion of crossvein mp 3+4 -cua is involved in forming the nodal line -while nodal line is more proximal then crossvein between in any other palaeontinoids. So, the evolutionary tendency of shifting to more apical position of this connection point is observed among the representatives of Palaeontinidae. It is interesting that the claval veins Pcu and A 1 are fused in apical ¼ of the clavus length. This is a very ancient feature of early Cicadomorpha, present among the Permian representatives of the suborder, but also in the Triassic Dunstaniidae 16 . It seems that line of claval margin is rather continued on postclaval margin (the specimen is damaged at this area suggesting the incision); the incisions suggested at this point in the Dunstaniidae 17 , seems to be an artifact of preservation. However, the obtuse angle of the clavus is a unique feature of the Hallakkungis gen. nov. Another remarkable feature of this fossil is the strong curving in median ⅓ of the branch CuA 2 , such a character is not known among the other Palaeontinidae. It is interesting, that the corrugation at margin of the forewing is found also in some Early Cretaceous Palaeontinidae 21 , but such a feature is present also in taxa not related to the Palaeontinioidea representatives of the Cicadoidea: Cicadidae and Cercopoidea: Cercopidae 26,27 .
The newly described above genus and species presents a mixture of plesiomorphic, ancestral features shared with the Triassic Dunstaniidae, apomorphic, derived features found in the Jurassic and Cretaceous palaeontinids, and strongly autapomorphic features. General trends could be observed: the narrowing of the costal lobe, the progressively proximal separation of RA and RP, the development of a long basal crossvein between MP and CuA, so that the basal part of the wing comes to be supported by a three pronged fork of ScP + RA, RP and MP, rather than ScP + RA + RP, MP and CuA. The abovementioned features places this specimen among the unique taxa. Hallakkungis gen. nov., is an important link to understanding the evolutionary trends, tendencies and traits of early Palaeontinidae. This new fossil genus of Palaeontinidae comes from the deposits of the Late Triassic Daedong flora, which is a typical representative of the Dictyophyllum-Clathropteris flora of Asia. It contains a number of plant taxa typical of the Triassic or to be relicts of the Permian floras 10 . The great reconstruction of the face of the Earth and of the organic world (the appearance of a great number of new plant forms) started in the Middle Triassic, and has been completed to the end of the Triassic. This distributional pattern of plants remained relatively stable during the rest of Mesophytic. Hence, this could be the source of evolutionary success of phytophagous, phloem-feeding Palaeontinidae.
The new discovery presented above is also the first record of the family Palaeontinidae from the Upper Triassic of Korea. We anticipate discovery of more well-preserved specimens from South Korea that will allow us to carry out more morphological and taxonomic studies, as well as palaeoecological, palaeobiogeograpical and evolutionary analyses of the Palaeontinidae and its relatives.