The Xiaheyan locality (Ningxia, China) is a Late Carboniferous outcrop providing insects in very large abundance, i.e. at least an order of magnitude above known contemporaneous localities. Several of the described species are represented by tens of specimens, including some with both forewings preserved attached to the pterothorax. This exceptional material allowed solid inferences on wing venation intra-specific variability in various insect lineages (e.g. Béthoux et al., 2011, 2012b; Cui et al., 2011; Gu et al., 2011; Li et al., 2013; Pecharová et al., 2015). Moreover, both males and females were identified for two species (Du et al., 2017; Pecharová et al., 2015), one of them, a relative of grasshoppers, crickets and katydids (Orthoptera), displaying a significant female-biased sexual size dimorphism. Such data are essential to better delimit early insect species, a chronic issue, and in particular for those species with no relevant extant counterparts (Béthoux, 2009).

The current overview of the insect fauna (or, at least, the taphocoenosis) suggests that it is dominated by stem lineages of Orthoptera. Most of the species described to date are comparatively remote relatives of Orthoptera (Archaeorthoptera nec Panorthoptera). Panorthoptera, a taxon including species more closely related to crown Orthoptera, are represented by a single species, Heterologus duyiwuer Béthoux, Gu and Ren, 2012a, with a single forewing described. Herein we describe the second species of Panorthoptera from this fauna, also documented by a single forewing, which displays a unique combination of character states.

The studied specimen is housed at the Key Lab of Insect Evolution and Environmental Changes, College of Life Sciences, Capital Normal University, Beijing, China (CNU). It was collected from the locality near Xiaheyan village, Zhongwei City, Ningxia Hui Autonomous Region, China. The exact layer from which it was collected was not documented. Previous studies suggested a Namurian B/C/early Bashkirian age for the whole locality (Lu et al., 2002; Zhang et al., 2013), but ongoing studies (Trümper et al., 2017) are revealing that the locality is probably younger. A Moscovian age is more likely for the higher insect-bearing horizons.

A draft drawing was produced using a Leica MZ12.5 dissecting microscope equipped with a drawing tube (Leica, Wetzlar, Germany). It was finalized using Adobe Illustrator CS6 (Adobe Systems, San Jose, CA, USA). The photograph was taken using a digital camera Canon 5D Mark III (Canon, Tokyo, Japan), coupled to a Canon MP-E 65 mm macro lens equipped with a polarizing filter. The resulting photograph was optimized using Adobe Photoshop CS6.

We follow the serial insect wing venation ground pattern (Lameere, 1922, 1923). The corresponding wing venation nomenclature is repeated for convenience: ScP, posterior subcosta; R, radius; RA, anterior radius; RP, posterior radius; M, media; MA, anterior media; MP, posterior media; Cu, cubitus; CuA, anterior cubitus (indicated by an asterisk in Fig. 1); CuP, posterior cubitus; CuPa, anterior branch of CuP; CuPaα, anterior branch of CuPa; CuPaβ, posterior branch of CuPa; CuPb, posterior branch of CuP; AA, anterior analis. Based on this ground pattern we follow topographic homology conjectures proposed by Béthoux and Nel (2002, 2001) for total Orthoptera (see Du et al., 2017, for references on alternative proposals and the associated discussion).

Taxon Archaeorthoptera Bethoux and Nel, 2002

Type species: Sinogerarus pectinatus spec. nov.Gender: Masculine.Etymology: A combination of “Sino”, referring to the geographic origin of the holotype, and Gerarus, a genus name used for species sharing similarities with the new one.Diagnosis: By monotypy, as for the type species.

Sinogerarus pectinatus Gu, Béthoux and Ren spec. nov.

Most “geraridaeans” and all “oedischioideans” display a fork of M located shortly after the point of divergence of M from M + CuA (Béthoux and Nel, 2003; Carpenter, 1992; Gorochov, 1995; Kukalová-Peck and Brauckmann, 1992; Sharov, 1968, 1971; Zessin, 2009), unlike the new specimen, in which M is simple for ca. two-fifths of its length. Among “geraridaeans”, Gerarus fischeri (Brongniart, 1885) (revised in Béthoux and Nel, 2003) and Osnogerarus trecwithiensis Kukalová-Peck and Brauckmann, 1992 (revised in Brauckmann and Herd, 2006 – including a drawing by O. Béthoux) both display a comparatively distal first fork of M. Yet the new specimen can be distinguished from both species (and most “oedischioideans”) owing to the lack of “connection” (actual fusion or connection via a short cross-vein) between RP and MA. Moreover, cross-venation is denser in G. fisheri and O. trecwithiensis and does not tend to form intercalary pseudo-veins in the apical area. Finally, the forked CuPb precludes an assignment of the new specimen to the “oedischioideans”, in which this vein is always simple.

The very regular branching pattern of RP and the apparent distal fork of M are reminiscent of the Caloneurodea, but (1) according to Béthoux et al. (2004) the apparent distal fork of M in Caloneurodea is actually the first fork of MA, the first fork of M being super-imposed with the M/CuA fork (there is no evidence of such fusion in the new specimen) and (2) in Caloneurodea CuA + CuPaα (actually MP + CuA + CuPaα) is simple (if with an anterior branch, it then corresponds to MP; CuA + CuPaα is richly branched in the new specimen). Note that Spiculum mendicum Brauckmann and Herd, 2006 is a candidate Caloneurodea. Affinities with this order can be excluded.

Among the “unplaced” Panorthoptera species, B. magnificus has a fusion of CuPaα located opposite the point of divergence of M and CuA. In other words, there is no free part of CuA emerging from M + CuA, unlike in the new specimen (asterisk in Fig. 1). Several other features (cross-venation, branching pattern of RP, etc.) allow the new specimen to be differentiated from B. magnificus. After its late branching of M, the new specimen resembles Heterologus langfordorum Carpenter, 1944, but this species does not display the regular branching pattern of RP, MP and CuA + CuPaα; it also has a simple CuPb (forked distally in the new specimen). The new specimen maybe shares the most numerous similarities with H. duyiwuer (from the same locality; provisionally assigned to the genus Heterologus in the original description), including the distal first fork of M and the forked CuPb. The most conspicuous difference regards the cross-venation (reticulation occurs only in the distal-most areas in the forewing in H. duyiwuer). Also, branches of CuA + CuPaα are emitted regularly in the new specimen, while in H. duyiwuer there is a long distance between the point of divergence of the first and second posterior branches. Based on the available data, the new specimen has a forewing more elongate than that of H. duyiwuer. A number of additional species which are putative stem Orthoptera (see Brauckmann and Herd, 2006) are documented based on very fragmentary material and therefore will not be discussed. We conclude that erecting a new genus and a new species is justified.

Sinogerarus pectinatus displays a combination of character states whose polarities are difficult to assess due to (1) the scarcity of non-“geraridaean” and non-“oedischioidean” Panorthoptera material and (2) the lack of identified immediate sister group of Panorthoptera. Even though it remains perplexing in some respects, the newly described species adds to the knowledge of a poorly documented set of Upper Carboniferous insects.