A new moth lacewing Guithone bethouxi gen. et sp. nov., is described from the Middle Jurassic Jiulongshan Formation (Inner Mongolia, China). This taxon is characterized by robust body, head retracted under pronotum, and remarkable costal space (expanded basad, narrowed distad). Herein, we propose a detailed definition of the lineages of Ithonidae sensu lato (moth lacewings, giant lacewings, and montane lacewings) based on extant groups in order to clarify the systematics of fossil species within the taxon. The comparison shows that Guithone bethouxi gen. et sp. nov. unquestionably represents the earliest true moth lacewing, implying that lineage differentiations within Ithonidae sensu lato must have taken place before the Middle Jurassic. Furthermore the new genus possessing some particular venation characters, such as irrecurrent humeral veinlet and simplified crossveination in radial sector, represents an important intermediate group in the evolution of Ithonidae sensu lato.
Three distinct family-level lineages have been assigned to the ithonid-like lacewings, namely “Ithonidae” sensu stricto (moth lacewings), “Polystoechotidae” (giant lacewings), and “Rapismatidae” (montane lacewings). Based on their phylogenetic analysis incorporating both molecular and morphological data, Winterton and Makarkin (2010) formally synonymized Polystoechotidae and Rapismatidae with Ithonidae. The new status of Ithonidae sensu lato has now been accepted (Yang et al. 2012; Wang et al. 2013; Makarkin et al. 2014). However, there is a possible source of confusion due to the use of taxonomic reference using an “-id” ending (such as “ithonid”), indicative of family-level rank, and because of the various senses given to “Ithonidae”. In the following we propose to refer to the ithonid, polystoechotid and rapismatid genus-groups.
Although a few extinct genera were included (Allorapisma Makarkin and Archibald, 2009; Principiala Makarkin and Menon, 2007) in Winterton and Makarkin's (2010) phylogenetic reconstruction, the systematic position of most fossil taxa remains to be clarified as they previously were collectively attributed to Ithonidae sensu lato without the further assignment (Makarkin et al. 2014). Therefore, essentially based on Winterton and Makarkin's (2010) results, herein we propose a workable definition for the three lineages of Ithonidae based on wing venation, and this attempt aims to better integrate data obtained from both fossil and extant forms.
Up to date, about 10 genera and 26 species ranging from the Early Jurassic to early Eocene were identified as Ithonidae sensu lato (Makarkin et al. 2014). Noteworthy, only the polystoechotid genus-group has been found in the earliest strata (Early to Late Jurassic) (Martynov 1925, 1937; Panfilov 1980; Ren et al. 2002), while major diversification of the rapismatid genus-group seems to have started in the Early Cretaceous (Makarkin and Menon 2007; Makarkin and Archibald 2009). To date, no genuine fossil of the ithonid genus-group has been described. Herein, a new, convincing moth lacewings fossil is described from the Middle Jurassic of northeastern China. The new insect shares the typical features of extant representatives of the ithonid genus-group, representing the earliest occurrence of this lineage.
Institutional abbreviations.—CNU, Capital Normal University, Beijing, China.
Other abbreviations.—A1–A3, anal veins; CuA, anterior cubitus; CuP, posterior cubitus; f, frenulum; hv, humeral veinlet; MA, anterior branches of media; MP, posterior branches of media; R1, first branch of radius; Rs, radial sector; Sc, subcosta; tr, trichosors (wing venation terminology after Barnard 1981).
Material and methods
The specimen which is the focus of this study (CNU-NEU-NN 2015003P/C) is deposited in the Key Lab of Insect Evolution & Environment Change, Capital Normal University, Beijing, China. Draft drawing was produced using a LEICA MZ75 dissecting microscope equipped with a drawing tube. Photographs used to produce the combined photographs on Fig. 1A1, B (see details below) were taken with a Canon EOS 5D Mark III digital camera, and photographs of Figs. 1A2 and 3A, B were taken with Canon EOS 70D digital camera, both of which coupled to a Canon MP-E 65 mm macro lens (all lenses equipped with polarizing filters), under dry condition.
Photographs in Fig. 1 were produced as follows. Original photographs used the “matrix white balance” technique (Cui et al. 2015). Both sides of the specimen were photographed under both dry and ethanol conditions. The “P-side” of the specimen was fragmented during collection, and those fragments were glued loosely. Rather than undertaking a hazardous physical res toration of the specimen, we opted for a digital reconstruction. Each “fragment” photograph was isolated (simultaneously on both dry and ethanol photographs). Fragments were then tightly adjusted using their outline, and landmarks from the other side of the specimen (CNU-NEU-NN2015003C). Two photographic combinations were then produced. The one reproduced on Fig. 1A is a combination of ethanol photographs of both sides of the specimen, and of the side CNU-NEU-NN2015003C under dry condition; the photograph reproduced on Fig. 1B is a combination of ethanol photographs of both sides of the specimen (combination techniques exemplified in Béthoux 2015).
Order Neuroptera Linnaeus, 1758
Family Ithonidae Newman, 1853 sensu Winterton and Makarkin (2010)
Genera included: Ithonid genus-group: Ithone Newman, 1838, Megalithone Riek, 1974, and Varnia Walker, 1860, Guithone gen. nov.; polystoechotid genus-group: Fontecilla Navás, 1931, Platystoechotes Carpenter, 1940, Polystoechotes Burmeister, 1839, Elektrithone Makarkin, Wedmann, and Weiterschan, 2014, Jurapolystoechotes Ren, Engel, and Lü, 2002, Kirgisella Martynov, 1925, Lasiosmylus Ren and Guo, 1996, Mesopolystoechus Martynov, 1937, Osmyloides Panfilov, 1980, Palaeopsychops Andersen, 2001, Paleopterocalla (Panfilov, 1980), Panfilovdvia (Panfilov, 1980), Polystoechotites Cockerell, 1908; rapismatid genus-group: Adamsiana Penny, 1996, Narodona Navás, 1929, Oliarces Banks, 1908, Rapisma McLachlan, 1866, Allorapisma Makarkin and Archibald, 2009, Principiala Makarkin and Menon, 2007.
Remarks.—Winterton and Makarkin (2010) proposed a broad definition of Ithonidae (sensu lato), inclusive of three traditional families. However, interrelationships within the family were not fully resolved due to the uncertain placement of some genera (e.g., Oliarces Banks, 1908; Platystoechotes Carpenter, 1940) and the absence of most fossil taxa in the analysis.
Because the systematics of fossil insects is essentially based on wing venation, herein we reviewed the subdivision of the family in the framework of Winterton and Makarkin's (2010) phylogenetic work and propose some putative diagnostic features of wing venation.
The first lineage to consider is the ithonid genus-group (moth lacewings) consisting of the three extant genera that are restricted to Australia. These genera share the following character states combination: distal parts of Sc and R1 separated; Sc and R1 reaching the anterior margin straightly before the apex of wing; MP fork distant to the wing base, beyond the MA divergence (from Rs); and MP2 dichotomous branched. Noteworthy, few fossil insects could undoubtedly be assigned to this lineage to date.
The polystoechotid genus-group (giant lacewings) includes three living genera, but this assemblage is not well grouped due to the lack of the definitive synapomorphic character (Winterton and Makarkin 2010). Considering the diverse fossil taxa related to this group (about ten extinct taxa are assigned to this group temporarily), we outlined some remarkable venational features, including: distal parts of Sc and R1 closely approximated in extant genera or evidently fused in the fossil taxa; Sc and R1 distinctly bent posteriad and terminating close to the wing apex; crossveins regularly arranged and presence of the least well-defined outer gradate series in radial sector; MP forked distant from wing base, beyond MA divergence.
The heterogeneous rapismatid genus-group is represented by four extant genera Adamsiana Penny, 1996, Narodona Navás, 1929, Oliarces, and Rapisma McLachlan, 1866 and two extinct genera Allorapisma and Principiala. Although this clade has not received a firm support in the phylogenetic analysis of Winterton and Makarkin (2010), they share some distinctive features, including: distal parts of Sc and R1 separated; Sc and R1 distinctly bent posteriad, and the ending close to the wing apex; numerous and irregular crossveins arranged in radial sector; MP forked proximad of MA divergence.
The abovementioned combinations of character states can be used to differentiate the three main lineages of the family. This work must be considered as a preliminary arrangement at the genus level, based on the available data. It could be greatly helpful to reconsider the classification of Ithonidae including both fossil and extant species in the future.
Stratigraphic and geographic range.—Jiulongshan Formation, Middle Jurassic; Daohugou Village, Shantou Township, Ningcheng County, Inner Mongolia, China.
Comparisons of Guithone gen. nov. with three lineages of Ithonidae. Putatively apomorphic states in bold. 1 Separated Sc and R1 occurs in all extant ithonid genus-group and most rapismatid genus-group (unknown in Principiala). In polystoechtid genus-group, the extant genera also have the separated Sc and R1, but Sc and R1 are distinctly approximated distad in fossil polystoechotid genus-group (e.g., Palaeopsychops Andersen, 2001) that is different to the other groups. 2Sc and R1 in ithonid genus-group commonly straightly (or slightly bent) reach the anterior margin, however, Sc and R1 in the other groups distinctly incline posteriad and ending close to wing apex. 3Regular arrangement of crossveins in radial sector occurs in extant giant genus-group. Although some Eocene giant genus-group also show the complicated crossvenation, these species generally possess one row of outer gradate series at least. Contrarily, crossveins in radial sector in the other groups are always numerous and irregularly arranged. Few and irregular crossveins as a particular state are only found in some fossil taxa, e.g., Guithone gen. nov., Lasiosmylus Ren and Guo, 1996, Paleopterocalla (Panfilov, 1980), Panfilovdvia (Panfilov, 1980).
Genus Guithone nov.
Etymology: From Chinese gu, ancient; and the extant genus name Ithone.
Type species: Guithone bethouxi gen. et sp. nov., monotypic, see below.
Diagnosis.—The same as for the monotypic type species.
Remarks.—Although the specimen of the type species of this genus is only sub-complete, useful characters could be investigated. The new genus is assigned to the Ithonidae according to the following characters: stout body, head hypognathous and concealed under pronotum, and extremely broad costal space at the base (Fig. 1A1, B). To determine the systematic position of Guithone gen. nov. within Ithonidae, a comparison was conducted between the new genus and the three main lineages (Table 1). It is noticeable that a simple humeral veinlet (irrecurrent) occurs in the new genus, in contrast to the other genera of Ithonidae that commonly possess the recurrent humeral veinlet. Makarkin et al. (2013) pointed that the recurrent humeral veinlet as an apomorphy of Neuroptera independently evolves in different families within this order. As for Ithonidae, the recurred humeral veinlet should be a possible synapomorphy of this family considering the general occurrence at most known genera. Essentially, the humeral veinlet of Guithone gen. nov. also exhibits a “recurrent trend” in comparison with other genera (Figs. 2A, B, 3A). Consequently we consider that the form of humeral veinlet in Guithone gen. nov. represents an intermediate state in the evolution of the character within the Ithonidae.
The Table 1 summarized the distribution of wing venation character states among three genus-groups of Ithonidae, as compared to the states exhibited by Guithone gen. nov. It shows that the new genus shares most character states with the ithonid genus-group. Therefore, we propose that Guithone gen. nov. should be assigned to this group, hence representing its eldest record of this lineage, as well as the first record in the Northern Hemisphere.
Stratigraphic and geographic range.—As for the type species by monotypy.
Etymology: In honour of Olivier Béthoux to acknowledge his sincere help to Bingyu Zheng.
Holotype: CNU-NEU-NN2015003P/C, a nearly completely preserved male specimen with clearly visible structures, and four overlapping, sub-complete wings, partially folded.
Type locality: Daohugou Village, Shantou Township, Ningcheng County, Inner Mongolia, China.
Type horizon: Jiulongshan Formation, Bathonian-Callovian boundary beds (165 Ma), Middle Jurassic.
Diagnosis.—Trichosors present along the anterior margin; humeral veinlet simple, not recurrent; costal crossveins sinuous at their base, with distal dichotomous forks (rarely trichotomous); Sc and R1 reaching the anterior margin separately; few crossveins in the radial sector; MP fork beyond the separation of MA from Rs.
Description.—Body: well preserved, ca. 14.5 mm long, robust, with few hairs on the surface; head hypognathous, concealed under pronotum, ca. 1.2 mm long; antennae not preserved; compound eyes large, as wide as the half of frons; ocelli absent; mandible stout, apical portion sharp; thorax stout, less hairy; scutums in mesoscutum nearly round on both sides; mesoscutum of similar size as metascutum; legs medium-sized (ca. 1.5 mm), covered by abundant setae; tarsal claws short, sharp, with arolium at base of each; abdomen stout. Gender masculine.
Forewing: slender, ca. 19.3 mm long and 5.2 mm wide as preserved; dense hairs along margin and veins. Trichosors distributed (Fig. 1A2) along the proximal half of anterior margin; nygmata not detected; costal area shrinking gradually from the base to apex (2.2 mm maximum width, 0.9 mm minimum width); humeral veinlet not recurrent (Figs. 2A, B, 3A); costal cross-veins slightly sinuous at the base, and dichotomously forked distally (rarely trichotomous); Sc and R1 separated distally, reaching the anterior margin before wing apex (Fig. 3B); subcostal space narrowed basad and broadened distad (possibly as a consequence of compression); Rs slightly zigzagged in distal portion, with 17 regularly pectinate branches; MA simple, and the divergence of MA close to the origin of Rs; MP forked beyond the divergence point of MA from Rs; MP2 only partly preserved, first fork near mid-length of wing; CuA simple; CuP pectinately branched; anal region well developed, A1–A3 each with 2–4 distal branches.
Hindwing: incompletely preserved, main veins hardly identifiable; trichosores not detected; frenulum well preserved, visible on both hindwings (Fig. 1B). Wing membrane tinged with irregular pale brown shades.
Ithonidae had its golden time in the Mesozoic, however, most fossil taxa of this family have no further subdivisions due to the lack of identified characters of the subclades. Based on available data, we aimed to provide some diagnostic wing venation features of the three principle lineages, which allowed us to preliminarily allocate fossil taxa to one of the three genus- groups. Additionally, a new, convincing moth lacewing is described from the Middle Jurassic of China, representing the first record of this lineage in the Northern Hemisphere. Before the finding of Guithone gen. nov., the Gondwanan origin of moth lacewings was inferred from the constricted distribution of the extant genera. Nevertheless, the new genus provides the new insights on the evolution of moth lacewings. It indicates that differentiation between the giant lacewings and moth lacewings must have occurred before the Middle Jurassic. Additionally, a remarkable disjunct distribution across the fossil and extant genera within the moth lacewings implies that the pattern of moth lacewings evolution was probably more complicated than previously thought.
We thank Olivier Béthoux (CR2P, Sorbonne Universités, Paris, France) for assistance with the production of combined photographs reproduced on Fig. 1, and critical comments on the manuscript organization and wording. We also thank Shaun L. Winterton (California State Arthropod Collection, California Department of Food and Agriculture, Sacramento, USA) and Vladimir N. Makar kin (Institute of Biology and Soil Sciences, Far Eastern Branch of the RAS, Vladivostok, Russia) for greatly helpful reviews. This work was supported by the National Basic Research Program of China (973 Program) (2012CB821906), National Science Foundation of China (grants 31230065, 31272352, 31301905, 41372013, and 41272006), China Postdoctoral Science Foundation (grant 2012T50113), Research Fund for the Doctoral Program of Higher Education of China (grant 20131108120005), Beijing Natural Science Foundation (grant 5132008), Great Wall Scholar and KEY project of the Beijing Municipal Commission of Education (KZ201310028033), and Program for Changjiang Scholars and Innovative Research Team in University (IRT13081).