Order: Coleoptera Linnaeus, 1758

Family: Staphylinidae Latreille, 1802

Subfamily: Oxytelinae Fleming, 1821

Tribe: Euphaniini Reitter, 1909

Genus Protodeleaster gen. nov

Type species. Protodeleaster glaber sp. nov, designated here.

Etymology. The generic name is a combination of the Latinized prefix proto-, meaning giving rise to, and Deleaster, the most common Recent genus of the tribe Euphaniini; it is of masculine gender.

Diagnosis. The genus can be separated from all other extinct and extant Oxytelinae by the following combination of characters: body relatively large and elongate, glabrous, impunctate; antenna filiform to moniliform, with apical five antennomeres slightly dilated; gular sutures very narrowly separated at middle of head; epistomal suture present, straight and entire; pronotum well margined laterally, transverse; exposed part of procoxae small and rounded, procoxal cavities open, procoxal fissure probably open; mesocoxal cavities contiguous; mesoscutellum relatively large and exposed; meso- and metatibiae armed with one or two distinct ridges; abdominal segment II relatively short, poorly sclerotized; abdominal segments III–VII each with a single pair of wide paratergites; and tergites without basolateral ridges.

Protodeleaster glaber sp. nov (Fig. 1 and Fig. 2)

Description. Female, body robust, glabrous; elytra and abdomen distinctly wider than head and prothorax.

Head: moderate in size, distinctly narrower than pronotum; widest across eyes; base of head slightly constricted to form a broad neck. Eyes moderate in size, convex. Antenna long, 11-segmented, apical five antennomeres slightly dilated; basal antennomere long; antennomere 2 shorter and narrower; 3 distinctly longer than 2; antennomeres 4–7 more or less elongate, each slightly longer than wide; antennomeres 8–10 each wider than long; antennomere 11 large, elongate oval in outline. Epistomal suture distinctly present, straight and entire. Gular sutures very narrowly separated, subparallel at middle of head, strongly divergent toward base and apex. Clypeus well developed, broad. Maxillary palpi 4-segmented, elongate; apical three palpomeres thick, subequal to each other in width; palpomere 2 elongate, oblique apically, 3 shorter than 2, apical palpomere 4 elongate, acuminate apically.

Thorax: pronotum transverse, about 1.4 times as wide as long, distinctly margined, widest at anterior third; lateral margin broadly sinuate; anterior and posterior margins truncate. Surface probably with impressions. Hypomeron broad and strongly deflexed. Mesoscutellum relatively large, subtriangular, with longitudinal impressed line in anterior part, posterior part exposed behind pronotum. Mesoventral process short, extending between mesocoxae nearly to middle. Metaventral process absent. Elytra bicolored, anterior part of each darker, posterior part lighter; elytra relatively short, not covering segment II, each elytron 1.8 times as long as wide, laterally slightly widened to apex; apex truncate. Elytral epipleural ridge present. Surface of elytra glabrous, impunctate, without distinct longitudinal striae.

Legs: exposed medial part of procoxae small, rounded and contiguous; procoxal cavities open posteriorly, procoxal fissure seemingly open; protrochanters distinct; profemora fusiform, robust; protibiae not preserved. Mesocoxae relatively small, somewhat rounded, contiguous; mesotrochanters tear-like, elongate; mesofemora robust, similar to profemora; mesotibiae thin, each with two longitudinal ridges. Middle tarsi partly preserved, apparently 5-segmented, basal four tarsomeres each relatively short, apical tarsomere elongate. Metacoxae subtriangular, contiguous, reaching posterolateral corners of metaventrite; metafemora very stout, fusiform; metatibiae thin, each with one longitudinal ridge visible.

Abdomen: relatively broad, with seven sterna visible; gradually widened towards apex, segment VII widest, VII and VIII strongly tapered to apex. Sternite II slightly narrower than III and relatively poorly sclerotized. Sternites II and III without basal midlongitudinal carina. Segments II to VII each with one pair of wide paratergites, tergites without basolateral ridges.

Female genital segment very small; a pair of distal gonocoxites present, gonocoxites subtriangular, apparently lacking styli.

Dimensions (in mm). Holotype, female, NIGP 152503a–b: body length (from anterior margin of head to apex of abdomen): 6.20; head length: 0.78, width: 0.76; pronotum length: 0.81, width: 1.15; Elytra length: 1.48. Paratype, female, NIGP 152504a–b: body length: 6.60; head length: 0.83, width: 0.81; pronotum length: 0.86, width: 1.22; Elytra length: 1.58.

Material. Holotype 152503a–b (Fig. 1). Paratype 152504a–b (Fig. 2); both are imprints, preserved as part and counterpart. The type specimens of the new species are deposited at the Nanjing Institute of Geology and Palaeontology, Nanjing, China.

Etymology. Derived from the Latin adjective glaber, meaning smooth (without setae).

Age and locality. Lower Cretaceous, Yixian Formation; Huangbanjigou Village, Shangyuan Township, Beipiao City, Liaoning Province, China.

The family Staphylinidae, one of the most diverse families of Animalia, has at least 59,304 species (Newton, unpublished data, January 2013) grouped into one extinct and 32 extant subfamilies (Bouchard et al., 2011 and Herman, 2001). Among the 32 recent subfamilies of rove beetles, Oxytelinae are the only ones with secretory openings on the basal margin of tergum IX (which is usually divided into two parts by tergum X, see Newton, 1982). However, the characteristic gland openings, which are generally hidden within segment VIII, are not easy to see even in extant beetles, and the normal retracted position of the genital segment (IX-X) in the fossils makes it impossible to ascertain their presence. Sternite II of this newly discovered species is, however, relatively well developed and distinctive, suggesting that the new genus can be attributed to Oxytelinae and more specifically the recent tribe Euphaniini Reitter, 1909 (Bouchard et al., 2011) on the basis of the following combination of characters: abdominal segments III to VII with only one pair of very broad paratergites per segment; procoxal cavities open; mesocoxae small and contiguous; and sternite II distinctly developed, but comparatively short and poorly sclerotized (Newton et al., 2000).

Among the six genera of the tribe Euphaniini (Deleaster, Euphanias, Mitosynum, Oxypius, Platydeleaster, and Syntomium), the new genus displays the most morphological resemblances to the recent genus Platydeleaster Schülke, 2003 (Fig. 3), which has been suggested to be a relatively basal member of the subfamily Oxytelinae (Schülke, 2003). This similarity includes general habitus (superficially Omaliinae-like), relatively large body size, antennal morphology (with a slight 5-segmented club), well-defined straight epistomal suture, well-margined pronotum, bicolored elytra, and slender legs. However, the new genus can be readily distinguished from Platydeleaster by the absence of distinct impressed rows of punctures on the elytra and the presence of a much broader pronotum and shorter elytra. It is noteworthy that the meso- and metatibiae of the new genus are distinctly armed with one or two longitudinal ridges, which is very rare among the subfamily Oxytelinae and the extant fauna of the whole family.

Among all Mesozoic fossil staphylinids, the new genus displays more features resembling some Jurassic fossil taxa originally attributed to the subfamily Omaliinae than those assigned to subfamily Oxytelinae. Specifically, this new genus most resembles Eophyllodrepa Ryvkin, 1985 and Porrhodromus Tikhomirova, 1968, two Mesozoic genera discovered from the Early or Middle Jurassic of Russia and Late Jurassic of Karatau, Kazakhstan, respectively (Ryvkin, 1985 and Tikhomirova, 1968). Compared to Eophyllodrepa (based on the original description), the new genus possesses a more elongate head, more slender antennae, shorter elytra and a broader abdominal segment VII. The new genus is also superficially similar to the Omaliine genus Porrhodromus (based on the original description), but can be easily separated from the latter by three features: 1)

the antenna of Protodeleaster is relatively long with the apical five antennomeres distinctly dilated, whereas only the apical antennomere of Porrhodromus is strongly enlarged;

Compared to Deleaster grandiceps, the much younger but only known fossil species of Euphaniini, Protodeleaster can be easily separated by having a wider pronotum and the antennae with the five apical antennomeres dilated.

Phylogenetically, Euphaniini was suggested to be a basal, well-isolated group of Oxytelinae, sister to all remaining oxytelines (Newton, 1982). The oldest known oxyteline genus, Mesoxytelus Tikhomirova, 1968, from the Late Jurassic of Karatau, Kazakhstan, possesses several characteristic features of the tribes Thinobiini (general shape of forebody, strongly rounded elytral apex, reminiscent of Thinobius Kiesenwetter, 1844 and Bledius Samouelle, 1819) and Oxytelini (three longitudinal ridges on pronotum, characteristic of most Oxytelus Gravenhorst, 1802 and Anotylus Thomson, 1859) (Makranczy, 2006), as well as apparently two pairs of paratergites on segments III–VII, like members of those tribes but unlike Euphaniini and Protodeleaster. Therefore, the proposed phylogenetic position of Euphaniini and the discovery of the more derived Mesoxytelus from the Late Jurassic together imply that the tribe Euphaniini is a very old lineage, probably having appeared at least as far back as the Late Jurassic.