A new fossil species of the extant genus Vicelva from mid‐Cretaceous Kachin amber (Coleoptera: Staphylinidae)

Abstract A new species of the extant staphylinid genus Vicelva Moore & Legner, V. rasilis sp. nov., is reported from mid‐Cretaceous Kachin amber of northern Myanmar. Vicelva rasilis is distinguishable from extant members of Vicelva by the smoother dorsal surface of head, pronotum and elytra, less prominent median projection of clypeus, unnotched mesal edge of mandibles, semiglabrous antennomere 6, and longer tarsomere 1. The pollen‐containing coprolite attached to the beetle and the crystals within the beetle body provide valuable information about the biology and taphonomy of the fossil.

only two described species of Vicelva in the extant fauna: the type species V. vandykei (Hatch) in western North America and probably the Far East of Russia (Herman, 2001;Ryabukhin, 1999), and V. altaica (Kastcheev) in Kazakhstan (Kastcheev, 2003).The type species was originally placed in Oxytelinae as Coprophilus vandykei Hatch (Hatch, 1957), and was later recognized as conspecific to V. paradoxica Moore & Legner (Moore, 1974;Moore & Legner, 1973).The second species was placed in a monospecific genus also in Oxytelinae by the original author (Kastcheev, 2003), and was transferred to Vicelva by Newton (2015).
Among Phloeocharinae, members of the extant genus Charhyphus have been described from Eocene Baltic amber (Shavrin & Kairišs, 2020;Yamamoto et al., 2022), and members of the extant genus Phloeocharis have been described from Late Cretaceous New Jersey amber (Chatzimanolis et al., 2013) and mid-Cretaceous Kachin amber (Yamamoto & Newton, 2023).An extinct genus, Angucharcotes Li et al. was also described from Kachin amber (Li et al., 2023).Cai et al. (2020) mentioned a specimen of Vicelva from Kachin amber.In this study, we provide detailed figures and a formal description for this specimen.The taphonomic implications of this specimen are also discussed.

| MATERIAL S AND ME THODS
The Kachin amber (Burmese amber) specimen studied herein (Figures 2-7) originated from amber mines near Noije Bum (26°20′ N, 96°36′ E), Hukawng Valley, Kachin State, northern Myanmar.The amber specimen is deposited in the Nanjing Institute of Geology and Palaeontology (NIGP), Chinese Academy of Sciences (CAS), Nanjing, China.The amber piece was trimmed with a small table saw, ground with emery paper of different grit sizes, and finally polished with polishing powder.
Photographs under incident light were taken with a Zeiss Discovery V20 stereo microscope.Widefield fluorescence images were captured with a Zeiss Axio Imager 2 light microscope combined with a fluorescence imaging system.Confocal images were obtained with a Zeiss LSM710 confocal laser scanning microscope, using the 488 nm (Argon) or 561 nm (DPSS 561-10) laser excitation line (Fu et al., 2021).Images were stacked with Helicon Focus   Diagnosis.Head dorsally smooth, without swellings (Figure 4a).

| Systematic position of Vicelva rasilis and comparison with extant relatives
The staphylinid subfamily Phloeocharinae is notoriously difficult to characterize as a group, and even in the modern more restricted concept the subfamily is probably not monophyletic.For example, Herman (1972) when proposing this modern definition cited only two possible derived characters shared by the genera (the structure of the hypopharynx, and the presence of certain cuticular processes on some abdominal terga) in support of the group, and both of these characters are invisible in the fossil described here due to its preservation with the inner mouthparts concealed and unfolded wings covering the abdominal terga.Nevertheless, the individual extant and extinct genera placed in this subfamily (see Introduction) are generally distinctive in appearance and characters, and this is especially true for the genus Vicelva.The two extant species of this genus are unique in appearance among staphylinids (e.g., for V. altaica see Figure 1a, and for V. vandykei see photos available online provided by the California Academy of Sciences, 2023a, 2023b).Vicelva rasilis shares this appearance (Figures 2 and 3) and the following unique combination of characters with extant Vicelva: body very elongate and parallel-sided; head large, elongate, with long slender antennae, broad weakly defined neck, strongly and acutely produced mandibles, protruding and multidentate clypeus of unique shape, and more or less concealed labrum with only anterolateral macrosetae visible from above (Figure 4a); pronotum elongate, widest in anterior half (Figure 4c); elytra short, reaching abdominal tergite III (Figure 4d); and legs slender with 5-segmented elongate tarsi (Figures 3b and   4g).The two extant species of Vicelva also have two pairs of basolateral ridges on the basal abdominal terga, two pairs of laterosclerites on most abdominal segments, and abdominal intersegmental membranes with a brick-wall pattern, but these characters in the fossil Both extant species of Vicelva are characterized by a strongly produced clypeus with a median tooth (prominent projection) and 2-3 further teeth immediately below that, concealing most of the labrum; vertex of head with a pair of smooth round swellings; and pronotum and elytra with longitudinal elevations and grooves (Figure 1; Kastcheev, 2003;Moore & Legner, 1973).In contrast, in V. rasilis, the clypeus is similar (in our interpretation) but the median projection is much less prominent and the lower pair of teeth are more distinctly separated from the upper median projection (Figure 4a), the head lacks the paired swellings (Figure 4a), and the pronotum lacks the longitudinal elevations and grooves (Figure 4c).The longitudinal ridges or grooves on the elytra, even if present in V. rasilis (which might be a taphonomic artifact), are much more indistinct (Figures 2a and 4d).The mesal edge of mandibles has a deep notch in V. vandykei and V. altaica (Figure 1b; Kastcheev, 2003: figure 3), which is absent in V. rasilis (Figure 4a,b).In V. vandykei and V. altaica, the first five antennomeres are semiglabrous, with sparse long setae only, and the apical six are densely pubescent (Figure 1a).In V. rasilis, the first six antennomeres are semiglabrous, and the apical five are densely pubescent (Figure 4a,b).Vicelva rasilis differs additionally from the extant congeners in the much longer tarsomere 1, which is subequal in length to tarsomere 5 (Figures 3b and 4g), while in the extant species, the tarsomere 1 is longer than 2-4 but only about half as long as tarsomere 5. Finally, the mesocoxae are well separated and the meso-metaventral junction externally appears to be a straight line in V. rasilis (Figure 3f), but the mesocoxae are only narrowly separated and the mesoventral process is sharply acute in V. vandykei (Figure 1b) and possibly also V. altaica according to the drawing by Kastcheev (2003).

| Pollen-containing coprolite associated with Vicelva rasilis
A cylindrical coprolite is attached to the lateral side of the metathorax of NIGP166145, composed of tricolpate pollen which likely belong to the eudicots (Figure 6).The general morphology of the coprolite is similar to fecal pellets of extant and fossil beetles reported previously (Klavins et al., 2005;Procheş & Johnson, 2009;Tihelka et al., 2021).
However, this coprolite is unlikely to be produced by Vicelva rasilis.Although nothing is known about the biology of extant Vicelva, the large and sharp mandibles of V. rasilis and its extant relatives suggest that they are suited to predation of other insects.It looks possible that V. rasilis searches on plants for prey, potentially including some pollen-feeding beetles.

| Crystals in the fossil and taphonomic implications
Insects trapped in amber generally have their external morphology well-preserved.However, the preservation quality of internal anatomy varies greatly (McCoy et al., 2016(McCoy et al., , 2018)).Some of them preserve exquisite soft tissue (e.g., Grimaldi et al., 1994;Li et al., 2021;Poinar & Hess, 1982;Van de Kamp et al., 2014) et al., 2019, 2021;Yin et al., 2022), while in the remaining cases, the interior may be a cavity or (partially) filled with high-Z materials, with no original structure discernible.The interior of the present specimen, NIGP166145, is mainly a hollow cavity, with more or less scattered crystals within it (Figure 7).The crystals are denser in the prothorax, and sparser in the metathorax and abdomen.
Very few studies paid attention to the mineralization happened in amber inclusions (e.g., Baroni-Urbani & Graeser, 1987;Garty et al., 1982;Martıńez-Delclòs et al., 2004).According to a recent study (Jiang et al., 2022), calcification and silicification are common in the preservation of fossils in the Kachin amber, forming mainly calcite, chalcedony and quartz.Some minor amount of carbonaceous material, pyrite, iron oxide and phyllosilicate minerals may also be present.In NIGP166145, two well-isolated crystals appear to be a hexagonal bipyramid or a pseudocube (Figure 8); therefore we suppose that these crystals are most likely quartz (Goldschmidt, 1922).Some organic matter might have served as the crystallization centers, which were then decayed after the formation of quartz, leaving an empty sphere within the crystal (Figure 7).
The specimen NIGP166145 has metallic greenish-blue color on the elytra, resulting from exceptional preservation of epicuticular multilayer reflectors (Cai et al., 2020).Cai et al. (2020) implied that the insects in amber with well-preserved structural color (and therefore well-preserved external cuticle) would likely also have internal organs preserved.The complete decomposition of internal structure and the formation of quartz crystals in this specimen, however, demonstrates that the preservation states of external and internal structures of amber inclusions are not always correlated, as sometimes also seen in Recent specimens.

AUTH O R CO
7.0.2,Zerene Stacker 1.04 and Adobe Photoshop CC, and were further processed in Adobe Photoshop CC to adjust brightness and contrast.Microtomographic data were obtained with a Zeiss Xradia 520 Versa 3D X-ray microscope at the micro-CT laboratory F I G U R E 1 Extant members of Vicelva.(a) Vicelva altaica, holotype.Photography by Kirill V. Makarov; (b) Dissection of Vicelva vandykei, female, collected from Alder Creek, Oregon. of NIGP and analyzed in VGStudio MAX 3.0.Scanning parameters were as follows: isotropic voxel size, 6.8202 μm; power, 4 W; acceleration voltage, 50 kV; exposure time, 1.5 s; projections, 2401.

Etymology.
The specific name, formed from the Latin adjective rasilis, refers to the overall simple and smooth dorsal surface of the head and prothorax.Locality and horizon.Amber mine located near Noije Bum Village, Tanai Township, Myitkyina District, Kachin State, Myanmar; unnamed horizon, mid-Cretaceous, Upper Albian to Lower Cenomanian.

F
I G U R E 5 X-ray microtomographic reconstruction of Vicelva rasilis sp.nov., holotype, NIGP166145.(a) Dorsal view; (b) Ventral view; (c) Lateral view.Scale bar: 1 mm.are not available due to the preservation state.The fossil has various wrinkles or crenulations or other surface irregularities, especially on the thoracic and abdominal venter (Figures and 4f-h), that are not present in the extant species, but which we interpret as taphonomic artifacts of preservation.Overall, the numerous and often unique characters shared by the extinct and extant species give us confidence that V. rasilis belongs in the genus Vicelva.

F
I G U R E 6 Pollen-containing coprolite associated with Vicelva rasilis, NIGP166145.The arrows in (c) indicate the three colpi in polar view.Scale bars: 50 μm in (a); 20 μm in (b, c).
, and some others preserve the more or less sclerotized genitalia (e.g., Bukejs et al., 2020; Li et al., 2022; Nabozhenko et al., 2020; Schmidt F I G U R E 7 Virtual slices of Vicelva rasilis, NIGP166145, based on X-ray microtomographic reconstruction, showing the crystals within the beetle body.(a, b, e) Horizontal sections; (c, d) Sagittal sections.Scale bars: 1 mm in (a-c); 400 μm in (d, e).F I G U R E 8 Examples of crystals within the body of Vicelva rasilis, NIGP166145, based on X-ray microtomographic reconstruction.LI et al.
NTR I B UTI O N S Yan-Da Li: Conceptualization (equal); investigation (lead); visualization (equal); writing -original draft (lead); writing -review and editing (lead).Alfred F. Newton: Investigation (lead); writing -original draft (equal); writing -review and editing (equal).Di-Ying Huang: Funding acquisition (equal); investigation (equal); writing -review and editing (equal).Chen-Yang Cai: Conceptualization (equal); funding acquisition (equal); investigation (equal); supervision (equal); writing -review and editing (equal).ACK N OWLED G EM ENTS We are grateful to Su-Ping Wu and Wei Liu (NIGP, CAS) for help with micro-CT reconstruction, Rong Huang (Institute of Soil Science, CAS) and Yan Fang (NIGP, CAS) for help with confocal microscopy, Jing-Jing Tang (NIGP, CAS) for help with widefield microscopy, Yun-Ke Song for help with identification of the crystals (Institute of Geochemistry, CAS), Kirill Makarov (Moscow State Pedagogical University) for providing the photo of V. altaica, and Denise Montelongo and Christopher Grinter (California Academy of Sciences) for providing the photos of the type specimens related to V. vandykei.Two reviewers provided helpful comments on the manuscript.Financial support was provided by the National Natural Science Foundation of China (41925008, 42288201, 42222201).Y.-D.L. is supported by a scholarship granted by the China Scholarship Council (202108320010) and the Bob Savage Memorial Fund of the University of Bristol.