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Fossils reshape the Sternorrhyncha evolutionary tree (Insecta, Hemiptera)

The Sternorrhyncha, which comprise about 18,700 described recent species, is a suborder of the Hemiptera, one of big five most diverse insect orders. In the modern fauna, these tiny phytophages comprise insects of great ecological and economic importance, like aphids (Aphidomorpha), scale insects (Coccidomorpha), whiteflies (Aleyrodomorpha) and psyllids (Psylloidea). Their evolutionary history can be traced back to the Late Carboniferous, but the early stages of their evolution and diversification is poorly understood, with two known extinct groups—Pincombeomorpha and Naibiomorpha variously placed in classifications and relationships hypotheses. Most of the recent Sternorrhyncha groups radiated rapidly during the Cretaceous. Here we report the new finding of very specialised sternorrhynchans found as inclusions in mid-Cretaceous amber from Kachin state (northern Myanmar), which represent another extinct lineage within this hemipteran suborder. These fossils, proposed to be placed in a new infraorder, are revealed to be related to whiteflies and psyllids. We present, also for the first time, the results of phylogenetic analyses covering extinct and extant lineages of the Sternorrhyncha.


Results
Phylogenetic analysis. We conducted Bayesian Inference (BI) and Maximum Parsimony (MP) analyses using morphological data to place the fossil taxa and resolve the relationships within Sternorrhyncha. Therefore, we mainly included those morphological characters that were also discernible in the fossils that were selected. The data matrix used for the analysis consisted of 10 taxa (Fulgoromorpha taken as an outgroup, and 9 Sternorrhyncha ingroups, including extinct groups, see Supplementary information 1 Table S1) and 42 characters (see Supplementary information 1 Table S2). The characters were treated as non-additive and unordered. The list of characters and the nexus file containing the character matrix is available in Appendix (Tables S1 and S2).
The detailed results of phylogenetic analyses are presented in the Appendix. Both phylogenetic methods (MP and BI) were highly congruent in their resultant topologies (Supplementary information 1 Figs S1, S2a-c). According to the resulting phylogenies, the fossil described below forms a group of its own (Fig. 1), included in a clade of Psylliformes, related to Psyllodea and Aleyrodomorpha, but deserving of recognition as a different infraorder.
Systematic palaeontology. Order Hemiptera Linnaeus, 1758.  Diagnosis. Imago. Head with compound eyes narrower than thorax. Eyes entirely rounded, postocular tumosity present; lateral ocelli placed dorsolaterally, near anterior angle of compound eye in dorsal view, median ocellus present. Antennae 10-segmented, with bases in frons to compound eyes, rhinaria scarce (?). Pronotum in mid line longer than mesopraescutum. Fore wing with thickened costal margin, basal portion of stem R + MP + CuA weak, distal portion of stem R + MP + CuA convex, forked at about half of fore wing length, branch RA short; pterostigmal area thickened. Etymology. The generic name is derived from the adjective 'dingla' meaning 'old' in Jingpho language, which is spoken in Kachin state where the amber originates from. Gender: feminine.

Diagnosis.
Vertex in mid line about as long as wide between compound eyes. Frons flat, widely triangularly incised at base. Antenna with 10th antennomere longer than penultimate one, widened, membranous apically, with terminal concavity. Pronotum about twice as wide as long. Mesopraescutum narrow, about as wide as pronotum; mesoscutum wide, with scutellar sutures not reaching anterior margin; mesoscutellum widely pentagonal. Fore wing with branch R forked anteriad of branch MP + CuA forking. Tip of clavus at level of MP + CuA forking. Hind wing with terminals RP and M subparallel and weakened in apical portion. Metafemur not thickened, metatibia without apical spines. Etymology. The specific epithet is derived from the noun 'shagri' meaning 'insect' in Jingpho language spoken in the Kachin State, when the amber was collected. Diagnosis. Pedicel (2nd antennomere) elongate, slightly thickened, 3rd antennomere longer than second and 4th; antennomeres 4th to 8th subequal in length. Protibia with row of thin setae in apicad half. Probasitarsomere about half as long as prodistitarsomere. Subgenital plate small, subquadrate, parameres long and narrow, parallel; about 3 times as long as wide at base, with hooked acute apex. Male anal tube tubular, slightly widening apicad, merely shorter than parameres.  Vertex about half as long as width of head with compound eyes; slightly narrower than wide at base; disc of vertex slightly concave; sutura coronalis absent. Scapus cyllindrical, longer than wide, pedicel slightly longer than scapus, barrel-shaped, wider than 3rd antennomere. Antennomere 3rd longer than 2nd antennomere (pedicel) antennomeres 5th to 9th subequal in length; antennomere 9th with subapical rhinarium; antennomere 10th (apical) longer then penultimate one, spoon-like widened apically, with rhinarium placed subapically. Median and lateral ocelli visible from above. Compound eyes large, not divided, with distinct, non-differentiated ommatidia; postocular protuberances narrow. Frons convex, with distinct triangular, concave median portion; median ocellus at margin with vertex; postclypeus and apical portion of loral plates distinctly incised to frons; postclypeus Fore wing about 2.5 times as long as wide; narrower at base, widening posteriad, rounded in apical margin; widest at ¾ of its length. Costal margin thickened, veins thick, distinctly elevated; basal portion of stem R + MP + CuA weak, distal portion of stem R + MP + CuA convex, forked at about half of forewing length, branch RA short; pterostigmal area thickened; common stem MP + CuA short, branches RP, MP and CuA parallel on membrane; areola postica absent; clavus present, with apex exceeding half of forewing, with single claval vein A 1 .

Dingla shagria
Hind wing about 0.8 times as long as forewing, with costal margin with two groups of regularly dispersed setae, basal group with seven longer and stiff setae and median group with 10 shorter, stout setae; terminals RP and M subparallel and weakened in apical portion.
Abdomen with segments III to VIII almost homonomic in length, widely connected to thorax, subgenital portion narrowing. Subgenital plate small, subquadrate, parameres long and narrow, parallel; about 3 times as long as wide at base, with hooked acute apex. Male anal tube tubular, slightly widening apicad, merely shorter than parameres.

Discussion
Dinglomorpha infraord. nov. forms a distinct group, nested within a clade of Psylliformes, related to Aleyrodomorpha: Aleyrodoidea and Psyllodea: Psylloidea, but deserving to be separated as a different infraorder (Figs. 1,  4). This new infraorder seems to be closer related, in terms of its morphological features, to Psylliformes, the group containing Protopsyllidioidea, Aleyrodomorpha, extinct Liadopsyllidae and modern Psylloidea. Dinglomorpha infraord. nov. shares some features with Aleyrodomorpha, e.g. the general structure of head capsule, retention of antennal processus terminalis, membranous mesoscutellum, well developed mesopostnotum, and in fore wing venation reduction of areola postica. Dinglomorpha presents a combination of unique features, such as vein ScP present as separate fold at the base of common stem R + MP + CuA and base of this stem weakened (this feature is autapomorphic for the group and not observable in any other Sternorrhyncha). The presence of 10 antennal segments (antennomeres) seems to be a very conservative feature, as a reduction of the number of antennomeres is the general morphological tendency observed in various sternorrhynchans 15 . The presence of a median ocellus directed anteriorly seems to be a symplesiomorphic condition retained in some basal sternorrhynchans, e.g. in Jurassic Liadopsyllidae, Cretaceous genera Yamis Drohojowska & Szwedo, 2015 and Shapashe Drohojowska & Szwedo, 2015 (Aleyrodidae), or Cretaceous Postopsyllidiidae 10,11,13,16 .
The general structure of the head capsule in Dingla gen. nov. partly resembles the pattern observed in Psylloidea, with a narrow frontal portion incised between enlarged genae 17 . On the other hand, the well developed www.nature.com/scientificreports/ postclypeus and anteclypeus, with large mandibular plates (lora), and bases of antennae placed distinctly in front of compound eye resemble the pattern present in Aleyrodidae 18 . The antennae of Dingla gen. nov. have rhinaria on the ultimate and penultimate antennomeres, which is different than in other Psylliformes. In Psylloidea rhinaria are present subapically on each of antennomeres 2, 4, 6, and 7, in the Aphalarinae, rhinaria are also present on antennomeres 3rd and 5th 19 , in Protopsyllididae rhinaria seems to be distributed on antennomeres 3rd to 10th. It is not clear in Postopsyliididae and Permopsyllididae 11,13 , but it is most probably the same as in Protopsyllididae. In recent species of Aleyrodidae, rhinaria are usually present on antennomeres 3rd, 5th, and 7th 20 , however, multiple rhinaria are known in extinct Gapenus rhinariatus Drohojowska & Szwedo, 2013 from the Lower Cretaceous Lebanese amber 21 .
The pronotum in Dingla gen. nov. is relatively large, most similar to the state in Postopsyllidium Grimaldi, 2003 (Postopsyllidiidae; see 13 ). In general appearance it is similar to the pronotum observed in other Psyllodea, however it is larger than in Psylloidea and Aleyrodoidea 14,17,18 . The mesopraescutum in Dinglomorpha infraord. nov. is narrow, partly covered by the posterior portion of the pronotum. In Aleyrodoidea the mesopraescutum is not covered by the pronotum, with the posterior margin angulate, incised to the mesoscutum 14,18 . In general appearance it is most similar in shape to the the mesocutum in Psylloidea 14 . The mesopraescutum is poorly known in Protopsyllidioidea. It is relatively small, diamond shaped and with the anterior portion covered under the pronotum in Postopsyllidium Grimaldi, 2003 13 . The mesoscutum of Dingla gen. nov. is quite large, as in Psylloidea and Aleyrodidae, but has a deep posterior incision in which the mesoscutellum is incised with its anterior portion. In Aleyrodidae the mesoscutellum is short, membranous, and its median portion could be incised in posterior margin of mesoscutum 18,[21][22][23][24][25] . The well-developed mesopostnotum is present in Dingla gen. nov. and Aleyrodidae, while it is not as distinct in Psylloidea 14,17 . The metascutum, metascutellum and metapostnotum in Dingla gen. nov. are poorly visible, probably less developed in comparison to Psylloidea or Aleyrodoidea 14,17,18 .
Venation of the fore wing in Dinglomorpha infraord. nov. is very peculiar. The costal margin is thickened, with carinate Pc, as in remaining Psyllodea. The costal break, characteristic of Psylloidea is missing here, however, the veins of costal complex are at least partly included in thickened ambient vein-this vein is well developed in Psylloidea. The structure of the basal portion of the fore wing in Dinglomorpha is very unusual-the basal portion of veins R + MP + CuA is weakened, with ScP separated as fold. The median portion of R + MP + CuA complex presents traces of independence of stem R and stem MP + CuA, the fork of this stem is placed basal of claval apex, stem R produces single RA and much longer RP. The homologisation of the second branch is uncertain-from the topographic position on the wing it seems more probable that it is an MP stem, and that CuA, with its fork (delimiting the areola postica), is reduced. A similar reduction of areola postica is observed in Aleyrodidae, but in whiteflies the MP stem is also reduced (weak or absent in extinct Bernaeinae; see 26,27 ), or absent in Aleyrodinae and Aleurodicinae 23 .
The early stages of Sternorrhyncha evolution are not well understood, which is reflected in doubts and incongruences in their classification hypotheses based on morphological, palaeontological and molecular data (Fig. 4). The classification and nomenclatorial history of the Sternorrhyncha is very complex 28 (see also Supplementary information 1). The division of the Sternorrhyncha into two independent lineages was already postulated by Börner 29 , leading to opinions of non-monophyletic (diphyletic) status of the suborder 26 . Those proposals result from palaeontological observations and interpretations of the independent origins of aphids + scale insects lineage and jumping plantlice + whiteflies lineage, as well as inclusion of Paleorrhyncha (paraphyletic Archescytinoidea) within Sternorrhyncha 12 .
Morphological characters supporting the monophyly of the Sternorrhyncha comprises the rostrum tightly attached to chest, mesonotum divided into sclerites (unknown state in Pincombeomorpha), and reduced (in vast majority) veinlet cua-cup at base of fore wing. Development of the stigmal area in Pincombeomorpha and Aphidomorpha + Naibiomorpha appears to be homoplastic, however this feature could be a local synapomorphy of this lineage. Numerous morphological details of extinct Pincombeomorpha are poorly known. In most cases only isolated wings are available as sources of data. Regarding venational patterns, Pincombeidae seems to be more similar to the Aphidomorpha + Coccidomorpha lineage 30,31 . The analysis of head and thorax structures presented by Wegierek 32 shows that the Aleyrodomorpha displays a set of apomorphies which are not found in other groups of Sternorrhyncha, and these features place Aleyrodomorpha as a sister group to other sternorrhynchans, but in an unresolved position with regards to Euhemiptera (Supplementary information 1 Fig. S4d). Molecular studies are incongruent with the fossil record and morphological analyses, postulating Sternorrhyncha as a monophylum (Supplementary information 1 Fig. S3a-c), a sister group to remaining hemipterans 1 . Molecular studies often place Aleyrodomorpha as sister group to other Sternorrhyncha 33-35 , while results of morphological analyses suggest Aleyrodomorpha as a sister group to Psyllodea 14,36 . See also Supplementary information 1 for more detailed comments on relationships within the Sternorrhyncha.
The oldest fossils ascribed to the Sternorrhyncha were recently reported from the Moscovian (Carboniferous) locality of Avion in Pas-de-Calais Basin, France 5 . This finding pushes back the history of the group (Fig. 4) and challenges the hypothesis of their direct descendance from the Paleorrhyncha Archescytinoidea, which are known from the Asselian (earliest Permian) as previously proposed 26,32 .
The fossil record of particular sternorrhynchan lineages and their diversification, palaeodiversity and palaeodisparity is very uneven (see Supplementary information 1). Early diversity of Psyllodea comprises various Protopsyllidioidea, which went extinct by the late Cretaceous 13 . Jurassic diversity of modern Psylloidea and Aleyrodoidea is poorly documented, however their diversification might have been hampered by competition from other sternorrhychans and phloem-feeders radiating at these times (planthoppers and some true-bugs). Jurassic Liadopsyllidae present many plesiomorphic conditions, suggesting that these insects were still very generalized in their morphology and not highly disparate, as observed among other sternorrhynchans. The morphology of the Aleyrodidae adults is also rather conservative and not highly disparate as we can observe from the Jurassic and Cretaceous fossils 25,27 . The evolutionary shift in the morphological disparity of whiteflies (their puparia, Scientific RepoRtS | (2020) 10:11390 | https://doi.org/10.1038/s41598-020-68220-x www.nature.com/scientificreports/ in fact) is most probably related to mid-Cretaceous biosphere reorganization 37 , resulting in the change of host plants from gymnosperms to angiosperms and co-radiation with them. The evolutionary scenario of Dinglomorpha infraord. nov. was probably also affected by these and, as result, these insects could be endemic to the mid-Cretaceous biota of Kachin amber forests, as has been observed among other insects 7 . The distinctness of Dinglomorpha infraord. nov. could be a result of their long, alas so far undocumented, evolutionary history on the West Burma terrane or even Gondwanaland. The geological history of this terrane is very complex [38][39][40]

conclusions
We described a new genus and species, representing a peculiar and disparate sternorrhynchan lineage, known so far only from Kachin amber. It extends the range of the known taxonomic diversity and morphological disparity of Sternorrhyncha. Its morphological characters led to the placement of Dinglomorpha as separate infraorder, sister to Aleyrodomorpha (Psylliformes). The morphological disparity of Dinglomorpha could be due to their isolation and separate evolutionary history on the West Burma terrane, which seems to have been influenced by ecological pressures and challenges related to the local biota. The features and fate of the fossils preserved in Kachin amber were shaped by major ecological changes during the Cretaceous, making Dinglomorpha an example of a highly specialized, short-lived lineage of the Sternorrhyncha. The results of the first phylogenetic analysis of all sternorrhynchan groups, which is presented here, confirmed the monophyly of Sternorrhyncha, revealed Pincombeomorpha as a sister group to the remaining lineages, and supported the hypothesis of separating them into two clades -Aphidiformes and Psylliformes. The finding described above gives additional insight into the systematics, diversity and disparity of the Sternorrhyncha. The palaeoecology of the new group seems to be related to tropical habitats of the West Burma terrane, at least since the time of its separation from Australia in the Late Jurassic. Dinglomorpha could be one of the groups of Gondwanan origin and therefore the finding is also important for understanding the palaeobiogeography and the evolutionary history of the fauna of the Kachin amber forest.

Material and methods
The studied specimens are inclusions in mid-Cretaceous amber from Burma (Myanmar). Two specimens were collected by Mr. Patrick Müller, and acquired by the Museum of Amber Inclusions, University of Gdańsk (MAIUG) and two more come from the collection of Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS). Specimens were cut, grinded and polished for better visibility.
The specimens were examined, photographed and measured using the Leica M205C, Nikon SMZ1500, Nikon SMZ1270, Nikon Eclipse E600 and Zeiss Axio.Imager digital microscopes platforms, with incident and transmitted light were used simultaneously as well as with fluorescent illumination. The illustrations were prepared with two image-editing software packages (CorelDraw X9, CorelPaintX9). Fourier Transform Infrared Spectra (Supplementary information 1 Fig. S3a-h) were obtained in the Amber Laboratory of the International Amber Association in Gdańsk, for the reasons and according to procedure proposed by Szwedo and Stroiński 45 .
Phylogenetic analyses were performed according to procedures described in Supplementary information 1. Matrix file is presented as Supplementary information 2.