Cretaceous Research 89 (2018) 98e106 Contents lists available at ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes Short communication Beetle with long ‘nose’dA bizarre stem scydmaenine in amber from Myanmar (Coleoptera: Staphylinidae: Scydmaeninae) * Ziwei Yin a, Chenyang Cai b, c, d, , Alfred F. Newton e a Department of Biology, College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, 200234, China b Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, 210008, China c School of Earth Sciences, University of Bristol, Bristol, BS8 1TQ, UK d Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing, 210008, China e Center for Integrative Research, Field Museum of Natural History, Chicago, IL, 60605, United States article info abstract Article history: The staphylinid subfamily Scydmaeninae is a diverse assemblage of small predaceous beetles, repre- Received 23 January 2018 sented by some 5360 extant and 51 extinct species. Recent explorations of Mesozoic scydmaenine fauna Received in revised form in Burmese, Canadian, French, and Spanish ambers have shed intriguing light on the early evolution, 11 March 2018 systematics, and particular aspects of predator-prey relationship among this group. However, in contrast Accepted in revised form 22 March 2018 to extant diversity, well-preserved fossils allowing for sufficient morphological studies and ecological Available online 23 March 2018 reconstructions are extremely rare. Here we report a highly advanced glandulariine scydmaenine, Nuegua elongata Yin, Cai & Newton, gen. et sp. nov., based on a large series of fifteen exquisitely pre- Keywords: Taxonomy served specimens entombed in mid-Cretaceous Burmese amber. The new genus strikingly displays an d Nuegua gen. n. extremely prolonged preocular region that accounts for over half of the head length a structure un- Preocular head elongation known among all known living and extinct scydmaenines, but analogous to that of certain groups of the Functional morphology modern Laemophloeidae, Curculionoidea, Salpingidae, and Staphylinidae. We provide a formal Palaeodiversity description of the new genus, compare it with the most probably related taxa, and discuss possible functions of this bizarre head elongation. The discovery highlights the morphological disparity and palaeodiversity of the subfamily Scydmaeninae in late Mesozoic. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction Steninae þ Euaesthetinae; that result also implied the long elytra in scydmaenines are probably secondary derived, rather than a ple- The ant-like stone beetles, or subfamily Scydmaeninae, repre- siomorphic trait of non-staphylinid beetles (Grebennikov and sent a diverse lineage of small, predaceous beetles, comprising Newton, 2009). Recent explorations of fossil scydmaenines in some 5360 extant and 51 extinct species (Newton, unpublished Burmese, Canadian, French and Spanish ambers proved that typical database) and accounting for about 8% of total staphylinid diversity scydmaenine body plan (long elytra) had been well-established (over 62820 species of the family Staphylinidae are currently during early to late Cretaceous (O'Keefe et al., 1997; Kirejtshuk known; Newton, 2017). Due to the presence of long elytra covering et al., 2015; Cai and Huang, 2016; Jałoszynski and Perkovsky, most or the entire abdomen, scydmaenines had been retained as a 2016; Jałoszynski and Peris, 2016; Jałoszynski et al., 2017a; Yin separate family for nearly 200 years (Leach, 1815). Based on a et al., 2018). Noting the oldest known representative of the comprehensive phylogenetic analysis of adult and larval “Staphylinine group”, Libanoeuaesthetus pentatarsus Lefebvre, Vin- morphology, the subfamily was placed in the monophyletic cent, Azar & Nel from Lebanese amber (120e135 Ma), is a member “Staphylinine group” of subfamilies, sister to a clade composed of of Euaesthetinae (Lefebvre et al., 2005), the Scydmaeninae as a whole may have originated no later than Middle Jurassic, at least comparable to the subfamilies Glypholomatine, Omaliinae, Oxy- * Corresponding author. Key Laboratory of Economic Stratigraphy and Palae- telinae, Piestinae, Scaphidiinae, Tachyporinae and Olisthaerinae ogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of already reported from Jurassic deposits (Cai et al., 2012a, b, 2013, Sciences, Nanjing, 210008, China. 2015; Cai and Huang, 2013). E-mail address: [email protected] (C. Cai). https://doi.org/10.1016/j.cretres.2018.03.019 0195-6671/© 2018 Elsevier Ltd. All rights reserved. Z. Yin et al. / Cretaceous Research 89 (2018) 98e106 99 While divergence time of Scydmaeninae and evolutionary species of Scydmaeninae based on fifteen well-preserved speci- routes of major scydmaenine clades can be estimated by phylo- mens in Cretaceous Burmese amber, and illustrate a new struc- genetic approaches from modern exemplars, the history of ture unknown in other extant and extinct members of the particular aspects of ecological adaptations, including habitus subfamily. choice, feeding habitat, and mating behavior, of extinct taxa can be traced only by fossils. For example, extant species of the tribe 2. Material and methods Mastigini are active diurnal predators feeding on caterpillars or scavenging on dead arthropods (Jałoszynski, 2016a). By contrast, All amber materials were obtained from the Hukawng Valley in their Eocene and Cretaceous ancestors were speculated to apply a northern Myanmar (2621033.4100N, 9643011.8800E). Maps showing highly modified ‘antennal setose trap’ during predation, probably amber-yielding locality were provided in Cruickshank and Ko specific on springtails, indicating shifts of feeding habits (prey (2003), Kania et al. (2015), and Yin et al. (2018). The minimum choice) might have occurred during the evolutionary history of age of Burmese amber is widely accepted as earliest Cenomanian this group (Jałoszynski, 2016a; Yin et al., 2017). In another case, (98.79 ± 0.62 Ma) based on recent U-Pb dating of zircons (Shi et al., the unique pair of ‘labial suckers’ of the mouthparts in modern 2012). However, other workers have argued a late Albian Stenichnus godarti (Latreille) of the tribe Glandulariini plays a (Cruickshank and Ko, 2003; Ross et al., 2010) or Albian- critical role during predation on heavily sclerotized oribatid and Cenomanian boundary (Rasnitsyn et al., 2016) in age. A total of uropodine mites (Jałoszynski, 2016b), and this structure was even fifteen specimens were examined, all of which belong to a single more derived (suckers were much larger) in its Mesozoic relative species. The holotype (SNUC-Paleo-0016) and ten paratypes (SNUC- Hyperstenichnus vendeanus Jałoszynski & Perrichot, suggesting an Paleo-0017e0021, SNUC-Paleo-0023e0027) are housed in the In- ancient origin of a specialized predation mode in the Stenichnus- sect Collection of the Shanghai Normal University, Shanghai, China like scydmaenines (Jałoszynski et al., 2017b). A general impres- (SNUC), four paratypes (NIGP166325e166327, 167527) are depos- sion is that aside from recent discoveries of most major scyd- ited in the Nanjing Institute of Geology and Palaeontology, Chinese maenine lineages from mid to late Cretaceous deposits, our Academy of Sciences, Nanjing, China (NIGP). Amber pieces used for knowledge of the early evolution and paleobiology of this group photomicrography were cut using a handheld engraving tool with a is still insufficient because of limited accession to material pre- diamond blade, and polished using sandpapers of different grain served in a good condition. And probably due to their minute sizes and rare earth polishing powder. body size, all extinct scydmaenines have been known from am- Observations were made using a Zeiss Axio Imager 2 light bers only, and not yet been recorded from compression fossils, microscope with a digital camera attached. The Zeiss Axio Imager which may of critical importance in deciphering ancestral char- 2 microscope was equipped with a mercury lamp and specific acter states of the subfamily. Here, we describe a new genus and filters for DAPI, eGFP and rhodamine. Photomicrographs with a Fig. 1. Holotype (SNUC-Paleo-0016) of Nuegua elongata gen. et sp. nov. A. Dorsal habitus. B. Ventral habitus. C. Head, in lateral view. D. Complete view of the amber (each grid of the bar represents 0.5 mm). Abbreviations: at ¼ apical tooth; sat ¼ subapical tooth. Scale bars: 0.5 mm in AeB; 0.2 mm in C. 100 Z. Yin et al. / Cretaceous Research 89 (2018) 98e106 Z. Yin et al. / Cretaceous Research 89 (2018) 98e106 101 green background were taken under the eGFP mode. Other im- (Fig. 2C; lb) short, transverse, slightly curved at anterior margin; ages were made using a Canon 5D Mark III camera with a Canon antennal insertions moderately broadly separated; compound MP-E 65 mm macro lens (F2.8, 1e5X) or an Olympus Plan C 10Â eyes (Figs 2BeD, 3A; ce) markedly prominent and located sub- Objective Lens; and a Canon MT-24EX twin flash was used as light medially. Head finely setose along tempora, lacking thick bristles source. Zerene Stacker Version 1.04 was used for image stacking. on tempora and genae (Fig. 2D; gen). Antennae (Fig. 2A) longer All images were modified and grouped into plates in Adobe than head and pronotum together, antennomeres (Fig. 2A; a1e11) Photoshop CS5 Extended. each longer than wide, with subcylindrical proximal