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The first fossil Megalopsidiinae (Coleoptera: Staphylinidae) from Upper Cretaceous Burmese amber and its potential for understanding basal relationships of rove beetles
Cretaceous Research 59 (2016) 140e146
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The first fossil Megalopsidiinae (Coleoptera: Staphylinidae) from Upper Cretaceous Burmese amber and its potential for understanding basal relationships of rove beetles Shûhei Yamamoto a, b, *, Alexey Solodovnikov c a b c
Entomological Laboratory, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan Japan Society for the Promotion of Science Research Fellow (DC), Japan Natural History Museum of Denmark, Biosystematics Section, Zoological Museum, Universitetsparken 15, DK-2100 Copenhagen, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 August 2015 Received in revised form 18 October 2015 Accepted in revised form 27 October 2015 Available online xxx
The first definitive fossil of the peculiar monotypic rove beetle subfamily Megalopsidiinae is described as a new species Megalopinus extinctus sp. n. It represents a stem lineage valuable for the study of the early diversification of Staphylinidae, where sister group relationships of Megalopsidiinae currently remain a big controversy. This discovery corroborates the Mesozoic origin of this subfamily implied by its presumably basal phylogenetic position within Staphylinidae and hitherto available fossil record for the family. Well preserved peculiar mouthparts of M. extinctus specialized similarly with recent Megalopinus suggest the same mode of feeding in Megalopsidiinae for nearly a hundred million years. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Megalopinus Burmite Cenomanian Myanmar New species
1. Introduction With more than 60,000 described species grouped in 32 extant subfamilies, the Staphylinidae (rove beetles) is currently recognized as the most speciose animal family (Solodovnikov et al., 2013). Within Staphylinidae, the monobasic subfamily Megalopsidiinae is a very distinct rove beetle lineage confined to the world (sub)tropics. Currently more than 430 species of Megalopsidiinae are known globally, most of which occur in the Neotropical region, and many in the Oriental region. However, the group is poorly represented in the Afrotropical region and absent from the Pacific islands. Because Megalopsidiinae are being rarely collected, they are usually described from very limited material. Apparently, the actual species diversity of the group is significantly higher than currently known. For example recent studies, especially by Puthz (2012a, 2012b), doubled the number of described species of the subfamily.
* Corresponding author. Entomological Laboratory, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan. E-mail address: [email protected] (S. Yamamoto). http://dx.doi.org/10.1016/j.cretres.2015.10.024 0195-6671/© 2015 Elsevier Ltd. All rights reserved.
In spite of such notable species diversity, overall Megalopsidiinae is a rather morphologically conservative lineage, where all species belong to a single genus Megalopinus Eichelbaum, 1915, with the clear morphological diagnosis. Megalopinus has very distinct habitus and can be easily discriminated from other rove beetles by its bulging eyes occupying most of the lateral head margin, short clubbed antennae inserted in front of the level of anterior margin of the eyes, a deeply bifurcate labrum, and 5-5-5 tarsal formula (Newton et al., 2000; Brunke et al., 2011). Biology and detailed life cycle of Megalopinus are still largely unknown. However, at least for some species of the genus we know that they are associated with fungus-infested wood such as branches of dead standing trees, or crevices under rotten fallen logs with fungal growth (Leschen and Newton, 2003). Occasionally, adults of some species were found from fungus-infested leaf litter on the forest floor (Naomi and Nomura, 2015). In spite of the recent progress in the alpha-taxonomic study of the global species diversity of Megalopinus, no phylogenetic hypothesis for this interesting genus has ever been proposed. Puthz (2012a, 2012b), however, abandoned a pre-phylogenetic, obviously artificial subgeneric division of this genus of the earlier authors (Benick, 1917, 1952; Scheerpeltz, 1972) and divided the genus into several informal species-groups instead.
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Similarly to the lack of phylogenetic knowledge about diversification within the genus Megalopinus, the origin and sister group relationships of that lineage within the family Staphylinidae are also largely unknown. Megalopsidiinae is believed to be a monophyletic group based on the morphological evidence (Thayer, 2005; Grebennikov and Newton, 2009) that is currently placed in the informal ‘Staphylinine group’ of rove beetle subfamilies (Lawrence and Newton, 1982, 1995; Newton and Thayer, 1992; Grebennikov and Newton, 2009). However, monophyly or composition of the ‘Staphylinine group’, as well as the sister group of Megalopsidiinae are controversial issues of rove beetle phylogeny. Hansen (1997) considered Megalopsidiinae as the least derived lineage of his ‘Stenine group’ that also included sister subfamilies Steninae and Euaesthetinae. In the morphology-based phylogenetic analysis of Leschen and Newton (2003), Megalopsidiinae is a sister group to the clade (Pseudopsinae, (Steninae þ Euaesthetinae)). In the taxonand character-wise more inclusive analysis of Grebennikov and Newton (2009), Megalopsidiinae is resolved as an even more isolated lineage of rove beetles that is sister to a clade formed by eight other subfamilies of the ‘Staphylinine group’, the latter including Solieriinae and Scydmaeninae. In the recent molecular phylogenetic study of Staphyliniformia (McKenna et al., 2015), Megalopsidiinae got a perplexing position as a lineage related to the ‘Oxyteline group’ of subfamilies far away from any of the subfamilies of the ‘Stenine group’ or even a more inclusive ‘Staphylinine group’. Incongruent results from various phylogenetic analyses of the recent species may indicate, among other possibilities, high rate of extinction for lineages in question, and therefore a necessity to include stem lineages in the studies of the respective deep divergences. Although Cai and Huang (2013) mentioned some compression fossil of Megalopsidiinae from the Lower Cretaceous Lushangfen Formation in China, no any extinct fossil representative of this subfamily has ever been described. Herein, we provide the first formal description of the extinct lineage of Megalopsidiinae that is a remarkable new species based on a single well preserved specimen in Cretaceous Burmese amber (Cenomanian) from Myanmar. Although the newly discovered extinct species is different in some character states from Megalopinus, lack of a comprehensive phylogeny of that species-rich genus, or even of a global overview of its morphological diversity, urged us to describe this species as a member of Megalopinus pending proper phylogenetic study. We also place the new finding in the context of the broader knowledge of megalopsidiine evolution and ecology.
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Fig. 1. Location of the studied amber deposit in Myanmar (red star: Hukawng Valley, Kachin, northern Myanmar). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
GmbH, Wetzlar, Germany), with an attached Canon 7D digital camera (Canon Inc., Tokyo, Japan). Photographs were later stacked using the automontage software CombineZM (Alan Hadley, UK). When photographs were taken, the amber piece was immersed in clove oil (Wako Pure Chemical Industries, Ltd., Osaka, Japan; refractive index: 1.52e1.55). This oil-immersion method reduces extra light reflections on amber surface and increases visibility of , 2007; Penney and an insect specimen inside (Crighton and Carrio Green, 2010). Morphological terminology generally follows Naomi (1986), Thayer (2005), and Naomi and Nomura (2015). The measurements were given in the maximum length.
2. Materials and methods The beetle specimen is embedded in a small, flattened, semicircular piece (10.1 7.3 3.4 mm) of clear-yellow coloured Burmese amber (burmite). The sole specimen came from the Hukawng Valley (Fig. 1), southwest of Maingkhwan in the state of Kachin, northern Myanmar (Burma). Recent commercial mining of Burmese amber has been limited to “Noije Bum” (26150 N, 96 340 E) only, close to Tanai Village (Grimaldi et al., 2002; Shi et al., 2012). Burmese amber was once thought as Eocene-Miocene in age, but it is currently considered as Late Cretaceous (earliest Cenomanian, ca. 99 Ma) based on UePb zircon dating (Shi et al., 2012). The palaeofauna of Burmese amber is diverse and reviewed by Grimaldi et al. (2002) and Ross et al. (2010). SY cut and polished the amber piece for observation. The beetle specimen is very well preserved, and observations at multiple angles are possible. The holotype is housed in the American Museum of Natural History (AMNH: D. Grimaldi), New York, NY, USA. Observations and photographies were conducted using two types of stereoscopic compound microscopes (Leica M205C and Leica S8 APO: Leica Microsystems
3. Systematic palaeontology Order: Coleoptera Linnaeus, 1758 Family: Staphylinidae Latreille, 1802 Subfamily: Megalopsidiinae Leng, 1920 Genus Megalopinus Eichelbaum, 1915 Megalopinus extinctus sp. n. (Figs. 2e6) Material. Holotype, female, specimen number AMNH Bu-SY2. Locality and horizon. Myanmar, Kachin State, Hukawng Valley, Burmese amber; Upper Cretaceous, lowermost Cenomanian. Diagnosis. Distinguishable from all extant species of Megalopinus by combination of the following character states: gular sutures moderately separated, sub-parallel-sided basally but divergent anteriorly; pronotum elongate, with two pairs of longitudinal sulci dorsally; elytra with three pairs of longitudinal sulci; mesocoxae
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Fig. 2. Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2. A, dorsal habitus; B, ventral habitus. Scale bar ¼ 1.0 mm (A, B).
separated by distance larger than width of mesocoxa; metaventrite elongate, with deep median groove widening both anteriorly and posteriorly; tarsomere 1 short, as long as each of next three tarsomeres. Description. Body narrowly elongate, sub-parallel-sided, medium in size, 2.9 mm in length (from apex of clypeus to apex of abdomen), glabrous, strongly glossy. Colour uniformly dark brown; antennae, mouthparts, legs, and abdominal segments beyond VII light brown.
Fig. 3. Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2, lateral habitus. Scale bar ¼ 1.0 mm.
Head (Figs. 2AeB, 4AeB) slightly wider than pronotum, medium in size, weakly transverse 0.62 mm long (from apex of clypeus to anterior margin of pronotum) and 0.74 mm wide (including eyes), very slightly convex anteriorly, widest at middle of eyes, with rim-like strong constriction on neck; antennae inserted in front of line drawn at anterior margin of eyes, concealed under frontal shelf; dorsal surface with deep and sparse punctures. Eyes bulging laterally, large, occupying most of lateral head margin. Vertex with large hump at median portion, margined by shallow impression. Gular sutures (Fig. 5B: arrow, gs) moderately separated, sub-parallel-sided basally but divergent anteriorly. Antenna (Fig. 4D) composed of 11 antennomeres, short, as long as head width, slender but last three antennomeres forming loose club; antennomere 1 (a1) long, thick, moderately dilated; a2 long and slender, rather strongly dilated; a3 long, much longer than a2; a4 as long as a5, much shorter than a3; antennomeres 6e8 ellipsoidal, shorter than a5; a9 transverse, heavily sclerotized; a10 much wider than a9, heavily sclerotized; a11 subcylindrical in sub-basal region and subconical in distal half, with weakly pointed apical margin; approximate lengths of antennomeres from antennal base to apex: 38: 30: 36: 20: 20: 14: 14: 14: 17: 19: 35. Antennal grooves short and indistinct. Labrum (Fig. 6) deeply bifurcate, each lobe with blunt, rounded apex, much longer than wide, not exceeding apices of mandibles, sparsely setose laterally. Mandibles (Fig. 6) slightly asymmetric, strongly incurved, falciform, acutely pointed apically, right one with at least one inner tooth observable. Maxillary palpus (Fig. 6) medium in length, four-segmented; palpomere 1 (mp1) small; mp2 long, slender, curved gently; mp3 dilated, moderately wider than mp2, much shorter than mp2; mp4 elongate, narrowing distally from middle to pointed apex, as wide as mp3, much longer than mp3. Labial palpus (Fig. 6) medium in length, three-segmented; palpomere 2 (lp2) small and short; palpomere 3 (lp3) large, much longer than lp2, spindle-shaped, widest at basal third. Pronotum (Figs. 2A, 4C) narrowly elongate (0.59 mm wide, 0.67 mm long; width/length ¼ 0.88), moderately narrower than head and elytra, widest around anterior third; apical pronotal corner nearly right-angled and sharply pointed; lateral margins sinuate, with two pairs of setae; dorsal surface sulcate and foveolate, with two pairs of longitudinal sulci; hypomera fused with prosternum. Procoxal cavities elongate oval, contiguous, small. Mesoventrite with pair of foveae basally. Mesocoxae widely separated by distance larger than width of mesocoxa. Intercoxal region not clearly visible, including border between mesoventrite and metaventrite. Metacoxae moderate in size, contiguous. Mesoscutellum trapezoidal, weakly transverse. Elytra (Figs. 2A, 4C, 4E) unicolourous, rather slender (each 0.62 mm long, from posterior margin of pronotum to anterior margin of elytron, 0.34 mm wide); hind margin almost truncate; dorsal surface with three pairs of longitudinal sulci, with sinuate-transverse impression at base; elytral humeral area obtuse-angled, with small pointed humeral denticle; elytral epipleuron (Fig. 4E) distinct but barely visible from above; acute in shape, narrowing posteriorly. Metaventrite elongate, with median groove divergent both anteriorly and posteriorly (Fig. 5B: arrow). Legs (Figs. 2B, 3, 4F, 5B) relatively long and slender, moderately setose; procoxae conical, protrochanters small; profemora slender, clavate; protibiae slender, slightly longer than profemora; protarsi short, five-segmented; protarsomeres 1e4 short, almost in same shape and size; fifth tarsomere moderately longer than third and fourth tarsomeres combined; mesocoxae approximately fusiform, mesotrochanters elongate; mesofemora clavate, slender; mesotibiae slender; mesotarsi fivesegmented; mesotarsomeres 1e4 short, almost in same shape and size; fifth tarsomere much longer than third and fourth tarsomeres combined; metacoxae acutely narrowing laterally;
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Fig. 4. Body parts of Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2. A, dorsal view of head; B, ventral view of head; C, dorsal view of head and pronotum; D, lateral view of head and antennae; E, lateral view of elytron; F, hind legs, showing metatarsomeres. Abbreviations: a, antennomere; t, tarsomere. Scale bars ¼ 0.5 mm (AeD), 0.3 mm (E, F).
metafemora as long as mesofemora, clavate; metatrochanters small, oval-elongate; metatibiae slender, as long as mesotibia (0.56 mm long); metatarsi five-segmented; metatarsomeres 1e4 short, almost in same shape and size; fifth tarsomere much longer than third and fourth tarsomeres combined. Claws simple and equal, without empodium. Abdomen (Figs. 2e3, 5) narrow, rather sub-parallel-sided, widest around segments IV and V, slightly narrower than elytra, gradually tapered posteriorly; tergites and sternites IIIeVI strongly transverse but those of segment VII less transverse; tergite III with five foveae along the basal line; tergite IV also with foveae but middle one inconspicuous; tergite V with five foveae with middle one indistinct; tergite VI with pair of small foveae, situated laterally; tergite VII lacks any impression, with very weakly sinuate, almost truncate, posterior margin; tergite VIII smooth, with rounded posterior margin; sternite III with several foveae along basal line (difficult to observe); sternite IV with several foveae (difficult to observe); sternite V with approximately ten foveae (difficult to observe); sternite VI with approximately ten foveae (difficult to observe); sternite VII with pair of small foveae, situated laterally; tergite VIII smooth, with rounded, rather pointed, posterior margin; sternite IX, narrowly elongate, each lobe-like. Lateroventrites consist of two pairs in each of third to seventh abdominal segments. Etymology. The epithet of the new species is the Latin adjective ‘extinct’ that is self-explanatory for an old fossil lineage.
4. Discussion The remarkable new species can be clearly assigned to the subfamily Megalopsidiinae based on the following character combination: large bulging eyes, antennae inserted in front of eyes, with distinct 3-segmented club, foveated dorsal surface of the body, 5-5-5 tarsal formula, and deeply bilobed labrum. It can be easily distinguished from the subfamilies Steninae or Euaesthetinae (two other members of the ‘Stenine group’ of Hansen, 1997) by deeply bilobed labrum and by foveated dorsal surface of the body. Additionally, from Steninae, M. extinctus differs in normal labium nonmodified into very long specialized prey-capture apparatus (absent only in a few Steninae), and more anterior antennal insertion (antennae inserted between eyes in Steninae). Additionally from some Euaesthetinae, it differs in 3-segmented antennal club (2segmented in many euaesthetines), and 5-5-5 tarsal formula (4-4-4 or 5-5-4 in some euaesthetines). At the same time M. extinctus shows a number of character states that are unusual in most species of Megalopinus, and based on which it can be easily distinguished from extant congeners. Those character states form the diagnosis of the new extinct species (see above). Also, an overall body shape of M. extinctus is much more slender compared to any other extant species of Megalopsidiinae. Many Megalopinus species have much wider elytra that are more or less projecting laterally, while in M. extinctus the elytra are much more slender, nearly parallel-sided, with pointed humeral angles. Also, in M. extinctus the elytra are unicolourous, while most (but not all) extant megalopsidiines
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Fig. 7. Extant species of Megalopsidiinae, Megalopinus sp., from Sulawesi Is., Indonesia. Scale bar ¼ 1.0 mm.
Fig. 5. Line drawings of Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2. A, dorsal habitus; B, ventral habitus. Abbreviation: gs, gular suture. Scale bar ¼ 1.0 mm.
usually have some colour pattern formed by few prominent yellow to reddish or orange spots on their elytra (Fig. 7) that is used for species identification in Megalopinus (e.g. Puthz, 2012a, 2012b; Naomi and Nomura, 2015). These peculiar characters of M. extinctus may well be apomorphies of a new species of Megalopinus. Without broad comparative morphological study and phylogenetic analysis of Megalopinus, however, we cannot be sure
Fig. 6. Mouthparts of Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2. A, photograph of enlarged mouthparts; B, line drawing of enlarged mouthparts. Abbreviations: lp, labial palpomere; mp, maxillary palpomere. Scale bar ¼ 0.1 mm (A, B).
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whether these differences indicate sister-group relationship of the new extinct species with the monophylym of all extant Megalopinus, or they are derived features of the extinct lineage nested within that genus in current sense. Thus, we regard and describe this species as a member of Megalopinus pending proper phylogenetic study of that genus. Highly specialized structures of mouthparts of M. extinctus, shared with those of extant Megalopinus, also support such solution. These specialized mouthparts of the fossil species including deeply bifurcate labrum that look exactly as in recent Megalopinus are particularly noteworthy. In combination with big eyes and other features shared with recent Megalopinus, such mouthparts structure suggest that M. extinctus perhaps had the same (or similar) predatory feeding mode and association with mesic habitats as those observed in recent Megalopinus. Feeding mode of extant Megalopinus involves a rotary mill or preoral sieving process which may act primarily as an efficient filtering mechanism developed in adults for predaceous feeding (Leschen and Newton, 2003). The peculiar shape of labrum acts like a sieve and strains digestible tissue from indigestible cuticle (Leschen and Newton, 2003). A striking similarity between the mouthpart structure of recent Megalopinus and M. extinctus could indicate about 100 million years of the evolutionary stasis in the feeding mode of Megalopsidiinae. Among rove beetles, based on fossil findings, remarkable evolutionary stasis has been suggested so far for the peculiar small subfamily Olisthaerinae known since Middle Jurassic (Cai et al., 2015), or for the Euaesthetinae genus Octavius known since Late Cretaceous (Clarke and Chatzimanolis, 2009). Clarke and Chatzimanolis (2009) also provided an overview of other examples of bradytely (slow rate of morphological evolution) among beetle and insect taxa. One of their conclusions is that at least in the reviewed beetle groups persistence of stable mesic habitats through the Earth history allowed some taxa confined to those habitats to remain unchanged through tens of millions of years of evolution. Also they mentioned ecological generality (lack of narrow specializations), or protection in ‘cloistered habitats’ (for example subcortical microhabitats for beetles) as some earlier proposed explanations for bradytely. Finally, they stressed lack of a uniform species diversity patterns among bradytelic taxa since the latter comprise both species-rich and species-poor lineages. In this respect, M. extinctus is very interesting since Megalopsidiinae is indeed a lineage confined to mesic habitats, and, as far as known, mostly associated with crevices of dead wood. Megalopinus is a species-rich genus with pan-tropical disjunct geographic distribution that, indirectly point to the antiquity of this genus. Whether its peculiar mouthparts indicate some narrow feeding specialization or, on the contrary, general adaptation for efficient predation on a variety of prey, remains unknown. Among other lines of evidence, potential bradytely of Megalopsidiinae and peculiar mouthparts shared by the extant Megalopinus and this new extinct species, urged us to downgrade some differences among the former and M. extinctus, and to consider them congeneric. A phylogenetic analysis of the extant and extinct Megalopsidiinae would be highly desirable to shed more light on the sister-group relationships and thus on the corresponding taxonomic status of M. extinctus. 5. Conclusions Megalopinus extinctus sp. n. is the first formally described fossil species belonging to the rove beetle subfamily Megalopsidiinae. Its discovery in the Upper Cretaceous amber along with the earlier brief mention of an undescribed compression fossil of megalopsidiine from the Lower Cretaceous Lushangfen Formation in China (Cai and Huang, 2013) indicate a long evolutionary history of
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this group dating back to the Mesozoic, and a probability for more fossils to be discovered. A possible pre-Cretaceous origin of the Megalopsidiinae, corroborated by both of these fossils, is consistent with the inferred age for other potentially closely related subfamilies of Staphylinidae (Grebennikov and Newton, 2012), some of which Mesozoic fossils are already known or are being recently discovered. Although M. extinctus possesses characters allowing to clearly place it in Megalopsidiinae, its morphology shows some unique features. Similar habitus and a number of distinct characters shared by M. extinctus with extant species of Megalopinus, especially characteristic mouthparts, as well as lack of any knowledge of the phylogeny of the presumably ancient and species-rich genus Megalopinus, urge us to consider the former as a congener of the latter. In its body shape more elongate than in extant Megalopinus, longer antennae with lesser pronounced club, and in shape of tarsi without elongate t1, M. extinctus shows some resemblance with Euaesthetinae. At the same time, in the body shape, large eyes and shape of antennae it somewhat resembles Steninae. In any case M. extinctus represents a stem lineage whose morphology should be used in the phylogenetic analysis along with relevant extant taxa, to infer its systematic position more rigorously, shed light on the early evolution of Megalopsidiinae, and to further test the hypothesis of Hansen (1997) of the close phylogenetic relationship of Megalopsidiinae with Euaesthetinae and Steninae. Since we are aware of at least three other stem and crown groups relevant for the study of the sister group relationships of these three subfamilies that are currently being studied, we postpone such character analysis until those taxa are named and their formal descriptions are published. Apart from the obvious phylogenetic significance of M. extinctus for rove beetle researchers, its exceptionally well preserved mouthparts showing the same morphological specialization as in recent Megalopinus are important for the reconstruction of the palaeoecology of Megalopsidiinae and understanding rates of evolution of the presumed bradytelic lineages. Acknowledgements We express deep gratitude to Dr. V. Puthz (Burgmuseum Schlitz, Germany) for giving his opinion about our fossil specimen. SY is grateful to Dr. T. Hirowatari (Kyushu University, Fukuoka, Japan) for critically reading and commenting on an earlier version of the _ manuscript, as well both of us acknowledge Dr. D. Zyła (Natural History Museum of Denmark) for her useful comments on the final version. SY also thanks Dr. S. Hosoishi (Kyushu University) for allowing SY to use a microscopic device for our study. Special thanks are also dedicated to Dr. D. Grimaldi (AMNH) for the acquisition of specimen number. We are grateful to two anonymous reviewers who provided helpful comments on the original version of this paper. This study was partially supported by the Grant-inAid for JSPS Fellows (14J02669) to SY from the Japan Society for the Promotion of Science. This is a contribution from the Entomological Laboratory, Faculty of Agriculture, Kyushu University, Fukuoka, Japan (Ser. 7, No. 21). References Benick, L., 1917. Neuer Beitrag zur Kenntnis der Megalopinen und Steninen (Col., Staphyl.). Entomologische Bl€ atter 13 (189e195), 291e314. Benick, L., 1952. Spezielles und Allgemeines über die Subfam. Megalopsidiinae (Col. €fer 47 (1951), Staph.). Entomologische Bl€ atter für Biologie und Systematik der Ka 58e87. Brunke, A., Newton, A.F., Klimaszewski, J., Majka, C., Marshall, S., 2011. Staphylinidae of eastern Canada and adjacent United States. Key to subfamilies; Staphylininae: tribes and subtribes, and species of Staphylinina. Canadian Journal of Arthropod Identification 12, 1e110. http://dx.doi.org/10.3752/cjai.2011.12. Cai, C.-Y., Huang, D., 2013. Mesozoic rove beetles from northeastern China
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(Coleoptera: Staphylinidae). In: 6th International Congress on Fossil Insects, Arthropods and Amber, Byblos, p. 13. Cai, C.-Y., Beattie, R., Huang, D., 2015. Jurassic olisthaerine rove beetles (Coleoptera: Staphylinidae): 165 million years of morphological and probably behavioral stasis. Gondwana Research 28, 425e431. http://dx.doi.org/10.1016/ j.gr.2014.03.007. Clarke, D.J., Chatzimanolis, S., 2009. Antiquity and long-term morphological stasis in a group of rove beetles (Coleoptera: Staphylinidae): description of the oldest Octavius species from Cretaceous Burmese amber and a review of the “euaesthetine subgroup” fossil record. Cretaceous Research 30, 1426e1434. http:// dx.doi.org/10.1016/j.cretres.2009.09.002. , V., 2007. Photography of amber inclusions in the collections Crighton, W.R., Carrio of National Museums Scotland. Scottish Journal of Geology 43, 89e96. http:// dx.doi.org/10.1144/sjg43020089. €tze zu meinem Katalog der StaphEichelbaum, F., 1915. Verbesserungen und Zusa ylinidengattungen aus dem Jahre 1909. Archiv für Naturgeschichte (A) 81 (5), 98e121. Grebennikov, V.V., Newton, A.F., 2009. Good-bye Scydmaenidae, or why the ant-like stone beetles should become megadiverse Staphylinidae sensu latissimo (Coleoptera). European Journal of Entomology 106, 275e301. Grebennikov, V.V., Newton, A.F., 2012. Detecting the basal dichotomies in the monophylum of carrion and rove beetles (Insecta: Coleoptera: Silphidae and Staphylinidae) with emphasis on the oxyteline group of subfamilies. Arthropod Systematics & Phylogeny 70, 133e165. Grimaldi, D., Engel, M.S., Nascimbene, P., 2002. Fossiliferous Cretaceous amber from Myanmar (Burma): its rediscovery, biotic diversity, and paleontological significance. American Museum Novitates 3361, 1e72. http://dx.doi.org/10.1206/ 0003-0082(2002)361<0001:FCAFMB>2.0.CO;2. Hansen, M., 1997. Phylogeny and classification of the staphyliniform beetle families (Coleoptera). Biologiske Skrifter, Det Kongelige Danske Videnskabernes Selskab 48, 1e339. ne rale et particulie re, des crustace s et Latreille, P.A., 1802. Histoire naturelle, ge des insectes, Vol. 3. F. Dufart, Paris. http://dx.doi.org/10.5962/ bhl.title.15764. Lawrence, J.F., Newton Jr., A.F., 1982. Evolution and classification of beetles. Annual Review of Ecology and Systematics 13, 261e290. http://dx.doi.org/10.1146/ annurev.es.13.110182.001401. Lawrence, J.F., Newton Jr., A.F., 1995. Families and subfamilies of Coleoptera (with selected genera, notes, references and data on family-group names). ski, S.A. (Eds.), Biology, Phylogeny, and Classification of In: Pakaluk, J., Slipi n Coleoptera. Papers Celebrating the 80th Birthday of Roy A. Crowson. Muzeum I Instytut Zoologii Polska Akademia Nauk, Warsaw, pp. 779e1006. Leng, C.W., 1920. Catalogue of the Coleoptera of America, North of Mexico. John D. Sherman, Jr., Mount Vernon, NY. Leschen, R.A., Newton, A.F., 2003. Larval description, adult feeding behavior, and phylogenetic placement of Megalopinus (Coleoptera: Staphylinidae). The Coleopterists Bulletin 57, 469e493. http://dx.doi.org/10.1649/586. Linnaeus, C., 1758. Systema naturae per regna tria naturae, secundum classes,
ordines, genera, species, cum characteribus, differentiis, synonymis, locis, Editio decima, reformata, Tomus I. Laurentii Salvii, Holmiae. McKenna, D.D., Farrell, B.D., Caterino, M.S., Farnum, C.W., Hawks, D.C., Maddison, D.R., Seago, A.E., Short, A.E.Z., Newton, A.F., Thayer, M.K., 2015. Phylogeny and evolution of Staphyliniformia and Scarabaeiformia: forest litter as a stepping stone for diversification of nonphytophagous beetles. Systematic Entomology 40, 35e60. http://dx.doi.org/10.1111/syen.12093. Naomi, S.-I., 1986. A taxonomic study on the subfamily Megalopininae (Coleoptera, Oxyporidae) of Japan, with descriptions of two new species. Kontyû 54, 344e352. Naomi, S.-I., Nomura, S., 2015. The genus Megalopinus Eichelbaum (Coleoptera, Staphylinidae, Megalopsidiinae) of Japan, with description of a new species. Elytra, Tokyo (N. S.) 5, 27e36. Newton, A.F., Thayer, M.K., 1992. Current classification and family-group names in Staphyliniformia (Coleoptera). Fieldiana Zoology (N. S.) 67, 1e92. http:// dx.doi.org/10.5962/bhl.title.3544. Newton, A.F., Thayer, M.K., Ashe, J.S., Chandler, D.S., 2000. Staphylinidae Latreille, 1802. In: Arnett, R.H., Thomas, M.C. (Eds.), American Beetles. CRC Press, Boca Raton, pp. 272e418. Penney, D., Green, D.I., 2010. Introduction, preparation, study & conservation of amber inclusions. In: Penney, D. (Ed.), Biodiversity of Fossils in Amber from the Major World Deposits. Siri Scientific Press, Manchester, pp. 5e21. Puthz, V., 2012a. Über die neuweltlichen Megalopinus-Arten (Coleoptera, Staphylinidae) (24. Beitrag zur Kenntnis der Megalopsidiinen). Linzer biologische €ge 44, 613e834. Beitra Puthz, V., 2012b. Über die Megalopinus-Arten der Orientalis (Coleoptera, Staphylinidae) (26. Beitrag zur Kenntnis der Megalopsidiinen). Linzer biologische €ge 44, 1373e1430. Beitra Ross, A., Mellish, C., York, P., Crighton, B., 2010. Burmese amber. In: Penney, D. (Ed.), Biodiversity of Fossils in Amber from the Major World Deposits. Siri Scientific Press, Manchester, pp. 208e235. l Scheerpeltz, O., 1972. Wissenschaftliche Ergebnisse der Studienreise von Gy. Topa nach Südwest-Argentinien (Coleoptera: Staphylinidae). Folia Entomologica Hungarica (N. S.) 25 (Supplement), 1e268 pls. 1e5. Shi, G., Grimaldi, D.A., Harlow, G.E., Wang, J., Wang, J., Yang, M., Lei, W., Li, Q., Li, X., 2012. Age constraint on Burmese amber based on U-Pb dating of zircons. Cretaceous Research 37, 155e163. http://dx.doi.org/10.1016/ j.cretres.2012.03.014. Solodovnikov, A., Yue, Y., Tarasov, S., Ren, D., 2013. Extinct and extant rove beetles meet in the matrix: Early Cretaceous fossils shed light on the evolution of a hyperdiverse insect lineage (Coleoptera: Staphylinidae: Staphylininae). Cladistics 29, 360e403. http://dx.doi.org/10.1111/j.1096-0031.2012.00433.x. Thayer, M.K., 2005. Staphylinidae Latreille, 1802. In: Beutel, R.G., Leschen, R.A.B. (Eds.), Coleoptera, Beetles, Morphology and Systematics (Archostemata, Adephaga, Myxophaga, Polyphaga Partim), Vol. 1. Walter de Gruyter, Berlin and New York, pp. 296e344. Handbook of Zoology, Vol. IV: Arthropoda: Insecta (Kristensen, N.P., Beutel, R.G., Eds.). Part 38.
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The first fossil Megalopsidiinae (Coleoptera: Staphylinidae) from Upper Cretaceous Burmese amber and its potential for understanding basal relationships of rove beetles Shûhei Yamamoto a, b, *, Alexey Solodovnikov c a b c
Entomological Laboratory, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan Japan Society for the Promotion of Science Research Fellow (DC), Japan Natural History Museum of Denmark, Biosystematics Section, Zoological Museum, Universitetsparken 15, DK-2100 Copenhagen, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 August 2015 Received in revised form 18 October 2015 Accepted in revised form 27 October 2015 Available online xxx
The first definitive fossil of the peculiar monotypic rove beetle subfamily Megalopsidiinae is described as a new species Megalopinus extinctus sp. n. It represents a stem lineage valuable for the study of the early diversification of Staphylinidae, where sister group relationships of Megalopsidiinae currently remain a big controversy. This discovery corroborates the Mesozoic origin of this subfamily implied by its presumably basal phylogenetic position within Staphylinidae and hitherto available fossil record for the family. Well preserved peculiar mouthparts of M. extinctus specialized similarly with recent Megalopinus suggest the same mode of feeding in Megalopsidiinae for nearly a hundred million years. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Megalopinus Burmite Cenomanian Myanmar New species
1. Introduction With more than 60,000 described species grouped in 32 extant subfamilies, the Staphylinidae (rove beetles) is currently recognized as the most speciose animal family (Solodovnikov et al., 2013). Within Staphylinidae, the monobasic subfamily Megalopsidiinae is a very distinct rove beetle lineage confined to the world (sub)tropics. Currently more than 430 species of Megalopsidiinae are known globally, most of which occur in the Neotropical region, and many in the Oriental region. However, the group is poorly represented in the Afrotropical region and absent from the Pacific islands. Because Megalopsidiinae are being rarely collected, they are usually described from very limited material. Apparently, the actual species diversity of the group is significantly higher than currently known. For example recent studies, especially by Puthz (2012a, 2012b), doubled the number of described species of the subfamily.
* Corresponding author. Entomological Laboratory, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan. E-mail address: [email protected] (S. Yamamoto). http://dx.doi.org/10.1016/j.cretres.2015.10.024 0195-6671/© 2015 Elsevier Ltd. All rights reserved.
In spite of such notable species diversity, overall Megalopsidiinae is a rather morphologically conservative lineage, where all species belong to a single genus Megalopinus Eichelbaum, 1915, with the clear morphological diagnosis. Megalopinus has very distinct habitus and can be easily discriminated from other rove beetles by its bulging eyes occupying most of the lateral head margin, short clubbed antennae inserted in front of the level of anterior margin of the eyes, a deeply bifurcate labrum, and 5-5-5 tarsal formula (Newton et al., 2000; Brunke et al., 2011). Biology and detailed life cycle of Megalopinus are still largely unknown. However, at least for some species of the genus we know that they are associated with fungus-infested wood such as branches of dead standing trees, or crevices under rotten fallen logs with fungal growth (Leschen and Newton, 2003). Occasionally, adults of some species were found from fungus-infested leaf litter on the forest floor (Naomi and Nomura, 2015). In spite of the recent progress in the alpha-taxonomic study of the global species diversity of Megalopinus, no phylogenetic hypothesis for this interesting genus has ever been proposed. Puthz (2012a, 2012b), however, abandoned a pre-phylogenetic, obviously artificial subgeneric division of this genus of the earlier authors (Benick, 1917, 1952; Scheerpeltz, 1972) and divided the genus into several informal species-groups instead.
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Similarly to the lack of phylogenetic knowledge about diversification within the genus Megalopinus, the origin and sister group relationships of that lineage within the family Staphylinidae are also largely unknown. Megalopsidiinae is believed to be a monophyletic group based on the morphological evidence (Thayer, 2005; Grebennikov and Newton, 2009) that is currently placed in the informal ‘Staphylinine group’ of rove beetle subfamilies (Lawrence and Newton, 1982, 1995; Newton and Thayer, 1992; Grebennikov and Newton, 2009). However, monophyly or composition of the ‘Staphylinine group’, as well as the sister group of Megalopsidiinae are controversial issues of rove beetle phylogeny. Hansen (1997) considered Megalopsidiinae as the least derived lineage of his ‘Stenine group’ that also included sister subfamilies Steninae and Euaesthetinae. In the morphology-based phylogenetic analysis of Leschen and Newton (2003), Megalopsidiinae is a sister group to the clade (Pseudopsinae, (Steninae þ Euaesthetinae)). In the taxonand character-wise more inclusive analysis of Grebennikov and Newton (2009), Megalopsidiinae is resolved as an even more isolated lineage of rove beetles that is sister to a clade formed by eight other subfamilies of the ‘Staphylinine group’, the latter including Solieriinae and Scydmaeninae. In the recent molecular phylogenetic study of Staphyliniformia (McKenna et al., 2015), Megalopsidiinae got a perplexing position as a lineage related to the ‘Oxyteline group’ of subfamilies far away from any of the subfamilies of the ‘Stenine group’ or even a more inclusive ‘Staphylinine group’. Incongruent results from various phylogenetic analyses of the recent species may indicate, among other possibilities, high rate of extinction for lineages in question, and therefore a necessity to include stem lineages in the studies of the respective deep divergences. Although Cai and Huang (2013) mentioned some compression fossil of Megalopsidiinae from the Lower Cretaceous Lushangfen Formation in China, no any extinct fossil representative of this subfamily has ever been described. Herein, we provide the first formal description of the extinct lineage of Megalopsidiinae that is a remarkable new species based on a single well preserved specimen in Cretaceous Burmese amber (Cenomanian) from Myanmar. Although the newly discovered extinct species is different in some character states from Megalopinus, lack of a comprehensive phylogeny of that species-rich genus, or even of a global overview of its morphological diversity, urged us to describe this species as a member of Megalopinus pending proper phylogenetic study. We also place the new finding in the context of the broader knowledge of megalopsidiine evolution and ecology.
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Fig. 1. Location of the studied amber deposit in Myanmar (red star: Hukawng Valley, Kachin, northern Myanmar). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
GmbH, Wetzlar, Germany), with an attached Canon 7D digital camera (Canon Inc., Tokyo, Japan). Photographs were later stacked using the automontage software CombineZM (Alan Hadley, UK). When photographs were taken, the amber piece was immersed in clove oil (Wako Pure Chemical Industries, Ltd., Osaka, Japan; refractive index: 1.52e1.55). This oil-immersion method reduces extra light reflections on amber surface and increases visibility of , 2007; Penney and an insect specimen inside (Crighton and Carrio Green, 2010). Morphological terminology generally follows Naomi (1986), Thayer (2005), and Naomi and Nomura (2015). The measurements were given in the maximum length.
2. Materials and methods The beetle specimen is embedded in a small, flattened, semicircular piece (10.1 7.3 3.4 mm) of clear-yellow coloured Burmese amber (burmite). The sole specimen came from the Hukawng Valley (Fig. 1), southwest of Maingkhwan in the state of Kachin, northern Myanmar (Burma). Recent commercial mining of Burmese amber has been limited to “Noije Bum” (26150 N, 96 340 E) only, close to Tanai Village (Grimaldi et al., 2002; Shi et al., 2012). Burmese amber was once thought as Eocene-Miocene in age, but it is currently considered as Late Cretaceous (earliest Cenomanian, ca. 99 Ma) based on UePb zircon dating (Shi et al., 2012). The palaeofauna of Burmese amber is diverse and reviewed by Grimaldi et al. (2002) and Ross et al. (2010). SY cut and polished the amber piece for observation. The beetle specimen is very well preserved, and observations at multiple angles are possible. The holotype is housed in the American Museum of Natural History (AMNH: D. Grimaldi), New York, NY, USA. Observations and photographies were conducted using two types of stereoscopic compound microscopes (Leica M205C and Leica S8 APO: Leica Microsystems
3. Systematic palaeontology Order: Coleoptera Linnaeus, 1758 Family: Staphylinidae Latreille, 1802 Subfamily: Megalopsidiinae Leng, 1920 Genus Megalopinus Eichelbaum, 1915 Megalopinus extinctus sp. n. (Figs. 2e6) Material. Holotype, female, specimen number AMNH Bu-SY2. Locality and horizon. Myanmar, Kachin State, Hukawng Valley, Burmese amber; Upper Cretaceous, lowermost Cenomanian. Diagnosis. Distinguishable from all extant species of Megalopinus by combination of the following character states: gular sutures moderately separated, sub-parallel-sided basally but divergent anteriorly; pronotum elongate, with two pairs of longitudinal sulci dorsally; elytra with three pairs of longitudinal sulci; mesocoxae
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Fig. 2. Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2. A, dorsal habitus; B, ventral habitus. Scale bar ¼ 1.0 mm (A, B).
separated by distance larger than width of mesocoxa; metaventrite elongate, with deep median groove widening both anteriorly and posteriorly; tarsomere 1 short, as long as each of next three tarsomeres. Description. Body narrowly elongate, sub-parallel-sided, medium in size, 2.9 mm in length (from apex of clypeus to apex of abdomen), glabrous, strongly glossy. Colour uniformly dark brown; antennae, mouthparts, legs, and abdominal segments beyond VII light brown.
Fig. 3. Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2, lateral habitus. Scale bar ¼ 1.0 mm.
Head (Figs. 2AeB, 4AeB) slightly wider than pronotum, medium in size, weakly transverse 0.62 mm long (from apex of clypeus to anterior margin of pronotum) and 0.74 mm wide (including eyes), very slightly convex anteriorly, widest at middle of eyes, with rim-like strong constriction on neck; antennae inserted in front of line drawn at anterior margin of eyes, concealed under frontal shelf; dorsal surface with deep and sparse punctures. Eyes bulging laterally, large, occupying most of lateral head margin. Vertex with large hump at median portion, margined by shallow impression. Gular sutures (Fig. 5B: arrow, gs) moderately separated, sub-parallel-sided basally but divergent anteriorly. Antenna (Fig. 4D) composed of 11 antennomeres, short, as long as head width, slender but last three antennomeres forming loose club; antennomere 1 (a1) long, thick, moderately dilated; a2 long and slender, rather strongly dilated; a3 long, much longer than a2; a4 as long as a5, much shorter than a3; antennomeres 6e8 ellipsoidal, shorter than a5; a9 transverse, heavily sclerotized; a10 much wider than a9, heavily sclerotized; a11 subcylindrical in sub-basal region and subconical in distal half, with weakly pointed apical margin; approximate lengths of antennomeres from antennal base to apex: 38: 30: 36: 20: 20: 14: 14: 14: 17: 19: 35. Antennal grooves short and indistinct. Labrum (Fig. 6) deeply bifurcate, each lobe with blunt, rounded apex, much longer than wide, not exceeding apices of mandibles, sparsely setose laterally. Mandibles (Fig. 6) slightly asymmetric, strongly incurved, falciform, acutely pointed apically, right one with at least one inner tooth observable. Maxillary palpus (Fig. 6) medium in length, four-segmented; palpomere 1 (mp1) small; mp2 long, slender, curved gently; mp3 dilated, moderately wider than mp2, much shorter than mp2; mp4 elongate, narrowing distally from middle to pointed apex, as wide as mp3, much longer than mp3. Labial palpus (Fig. 6) medium in length, three-segmented; palpomere 2 (lp2) small and short; palpomere 3 (lp3) large, much longer than lp2, spindle-shaped, widest at basal third. Pronotum (Figs. 2A, 4C) narrowly elongate (0.59 mm wide, 0.67 mm long; width/length ¼ 0.88), moderately narrower than head and elytra, widest around anterior third; apical pronotal corner nearly right-angled and sharply pointed; lateral margins sinuate, with two pairs of setae; dorsal surface sulcate and foveolate, with two pairs of longitudinal sulci; hypomera fused with prosternum. Procoxal cavities elongate oval, contiguous, small. Mesoventrite with pair of foveae basally. Mesocoxae widely separated by distance larger than width of mesocoxa. Intercoxal region not clearly visible, including border between mesoventrite and metaventrite. Metacoxae moderate in size, contiguous. Mesoscutellum trapezoidal, weakly transverse. Elytra (Figs. 2A, 4C, 4E) unicolourous, rather slender (each 0.62 mm long, from posterior margin of pronotum to anterior margin of elytron, 0.34 mm wide); hind margin almost truncate; dorsal surface with three pairs of longitudinal sulci, with sinuate-transverse impression at base; elytral humeral area obtuse-angled, with small pointed humeral denticle; elytral epipleuron (Fig. 4E) distinct but barely visible from above; acute in shape, narrowing posteriorly. Metaventrite elongate, with median groove divergent both anteriorly and posteriorly (Fig. 5B: arrow). Legs (Figs. 2B, 3, 4F, 5B) relatively long and slender, moderately setose; procoxae conical, protrochanters small; profemora slender, clavate; protibiae slender, slightly longer than profemora; protarsi short, five-segmented; protarsomeres 1e4 short, almost in same shape and size; fifth tarsomere moderately longer than third and fourth tarsomeres combined; mesocoxae approximately fusiform, mesotrochanters elongate; mesofemora clavate, slender; mesotibiae slender; mesotarsi fivesegmented; mesotarsomeres 1e4 short, almost in same shape and size; fifth tarsomere much longer than third and fourth tarsomeres combined; metacoxae acutely narrowing laterally;
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Fig. 4. Body parts of Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2. A, dorsal view of head; B, ventral view of head; C, dorsal view of head and pronotum; D, lateral view of head and antennae; E, lateral view of elytron; F, hind legs, showing metatarsomeres. Abbreviations: a, antennomere; t, tarsomere. Scale bars ¼ 0.5 mm (AeD), 0.3 mm (E, F).
metafemora as long as mesofemora, clavate; metatrochanters small, oval-elongate; metatibiae slender, as long as mesotibia (0.56 mm long); metatarsi five-segmented; metatarsomeres 1e4 short, almost in same shape and size; fifth tarsomere much longer than third and fourth tarsomeres combined. Claws simple and equal, without empodium. Abdomen (Figs. 2e3, 5) narrow, rather sub-parallel-sided, widest around segments IV and V, slightly narrower than elytra, gradually tapered posteriorly; tergites and sternites IIIeVI strongly transverse but those of segment VII less transverse; tergite III with five foveae along the basal line; tergite IV also with foveae but middle one inconspicuous; tergite V with five foveae with middle one indistinct; tergite VI with pair of small foveae, situated laterally; tergite VII lacks any impression, with very weakly sinuate, almost truncate, posterior margin; tergite VIII smooth, with rounded posterior margin; sternite III with several foveae along basal line (difficult to observe); sternite IV with several foveae (difficult to observe); sternite V with approximately ten foveae (difficult to observe); sternite VI with approximately ten foveae (difficult to observe); sternite VII with pair of small foveae, situated laterally; tergite VIII smooth, with rounded, rather pointed, posterior margin; sternite IX, narrowly elongate, each lobe-like. Lateroventrites consist of two pairs in each of third to seventh abdominal segments. Etymology. The epithet of the new species is the Latin adjective ‘extinct’ that is self-explanatory for an old fossil lineage.
4. Discussion The remarkable new species can be clearly assigned to the subfamily Megalopsidiinae based on the following character combination: large bulging eyes, antennae inserted in front of eyes, with distinct 3-segmented club, foveated dorsal surface of the body, 5-5-5 tarsal formula, and deeply bilobed labrum. It can be easily distinguished from the subfamilies Steninae or Euaesthetinae (two other members of the ‘Stenine group’ of Hansen, 1997) by deeply bilobed labrum and by foveated dorsal surface of the body. Additionally, from Steninae, M. extinctus differs in normal labium nonmodified into very long specialized prey-capture apparatus (absent only in a few Steninae), and more anterior antennal insertion (antennae inserted between eyes in Steninae). Additionally from some Euaesthetinae, it differs in 3-segmented antennal club (2segmented in many euaesthetines), and 5-5-5 tarsal formula (4-4-4 or 5-5-4 in some euaesthetines). At the same time M. extinctus shows a number of character states that are unusual in most species of Megalopinus, and based on which it can be easily distinguished from extant congeners. Those character states form the diagnosis of the new extinct species (see above). Also, an overall body shape of M. extinctus is much more slender compared to any other extant species of Megalopsidiinae. Many Megalopinus species have much wider elytra that are more or less projecting laterally, while in M. extinctus the elytra are much more slender, nearly parallel-sided, with pointed humeral angles. Also, in M. extinctus the elytra are unicolourous, while most (but not all) extant megalopsidiines
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Fig. 7. Extant species of Megalopsidiinae, Megalopinus sp., from Sulawesi Is., Indonesia. Scale bar ¼ 1.0 mm.
Fig. 5. Line drawings of Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2. A, dorsal habitus; B, ventral habitus. Abbreviation: gs, gular suture. Scale bar ¼ 1.0 mm.
usually have some colour pattern formed by few prominent yellow to reddish or orange spots on their elytra (Fig. 7) that is used for species identification in Megalopinus (e.g. Puthz, 2012a, 2012b; Naomi and Nomura, 2015). These peculiar characters of M. extinctus may well be apomorphies of a new species of Megalopinus. Without broad comparative morphological study and phylogenetic analysis of Megalopinus, however, we cannot be sure
Fig. 6. Mouthparts of Megalopinus extinctus sp. n., holotype, specimen number AMNH Bu-SY2. A, photograph of enlarged mouthparts; B, line drawing of enlarged mouthparts. Abbreviations: lp, labial palpomere; mp, maxillary palpomere. Scale bar ¼ 0.1 mm (A, B).
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whether these differences indicate sister-group relationship of the new extinct species with the monophylym of all extant Megalopinus, or they are derived features of the extinct lineage nested within that genus in current sense. Thus, we regard and describe this species as a member of Megalopinus pending proper phylogenetic study of that genus. Highly specialized structures of mouthparts of M. extinctus, shared with those of extant Megalopinus, also support such solution. These specialized mouthparts of the fossil species including deeply bifurcate labrum that look exactly as in recent Megalopinus are particularly noteworthy. In combination with big eyes and other features shared with recent Megalopinus, such mouthparts structure suggest that M. extinctus perhaps had the same (or similar) predatory feeding mode and association with mesic habitats as those observed in recent Megalopinus. Feeding mode of extant Megalopinus involves a rotary mill or preoral sieving process which may act primarily as an efficient filtering mechanism developed in adults for predaceous feeding (Leschen and Newton, 2003). The peculiar shape of labrum acts like a sieve and strains digestible tissue from indigestible cuticle (Leschen and Newton, 2003). A striking similarity between the mouthpart structure of recent Megalopinus and M. extinctus could indicate about 100 million years of the evolutionary stasis in the feeding mode of Megalopsidiinae. Among rove beetles, based on fossil findings, remarkable evolutionary stasis has been suggested so far for the peculiar small subfamily Olisthaerinae known since Middle Jurassic (Cai et al., 2015), or for the Euaesthetinae genus Octavius known since Late Cretaceous (Clarke and Chatzimanolis, 2009). Clarke and Chatzimanolis (2009) also provided an overview of other examples of bradytely (slow rate of morphological evolution) among beetle and insect taxa. One of their conclusions is that at least in the reviewed beetle groups persistence of stable mesic habitats through the Earth history allowed some taxa confined to those habitats to remain unchanged through tens of millions of years of evolution. Also they mentioned ecological generality (lack of narrow specializations), or protection in ‘cloistered habitats’ (for example subcortical microhabitats for beetles) as some earlier proposed explanations for bradytely. Finally, they stressed lack of a uniform species diversity patterns among bradytelic taxa since the latter comprise both species-rich and species-poor lineages. In this respect, M. extinctus is very interesting since Megalopsidiinae is indeed a lineage confined to mesic habitats, and, as far as known, mostly associated with crevices of dead wood. Megalopinus is a species-rich genus with pan-tropical disjunct geographic distribution that, indirectly point to the antiquity of this genus. Whether its peculiar mouthparts indicate some narrow feeding specialization or, on the contrary, general adaptation for efficient predation on a variety of prey, remains unknown. Among other lines of evidence, potential bradytely of Megalopsidiinae and peculiar mouthparts shared by the extant Megalopinus and this new extinct species, urged us to downgrade some differences among the former and M. extinctus, and to consider them congeneric. A phylogenetic analysis of the extant and extinct Megalopsidiinae would be highly desirable to shed more light on the sister-group relationships and thus on the corresponding taxonomic status of M. extinctus. 5. Conclusions Megalopinus extinctus sp. n. is the first formally described fossil species belonging to the rove beetle subfamily Megalopsidiinae. Its discovery in the Upper Cretaceous amber along with the earlier brief mention of an undescribed compression fossil of megalopsidiine from the Lower Cretaceous Lushangfen Formation in China (Cai and Huang, 2013) indicate a long evolutionary history of
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this group dating back to the Mesozoic, and a probability for more fossils to be discovered. A possible pre-Cretaceous origin of the Megalopsidiinae, corroborated by both of these fossils, is consistent with the inferred age for other potentially closely related subfamilies of Staphylinidae (Grebennikov and Newton, 2012), some of which Mesozoic fossils are already known or are being recently discovered. Although M. extinctus possesses characters allowing to clearly place it in Megalopsidiinae, its morphology shows some unique features. Similar habitus and a number of distinct characters shared by M. extinctus with extant species of Megalopinus, especially characteristic mouthparts, as well as lack of any knowledge of the phylogeny of the presumably ancient and species-rich genus Megalopinus, urge us to consider the former as a congener of the latter. In its body shape more elongate than in extant Megalopinus, longer antennae with lesser pronounced club, and in shape of tarsi without elongate t1, M. extinctus shows some resemblance with Euaesthetinae. At the same time, in the body shape, large eyes and shape of antennae it somewhat resembles Steninae. In any case M. extinctus represents a stem lineage whose morphology should be used in the phylogenetic analysis along with relevant extant taxa, to infer its systematic position more rigorously, shed light on the early evolution of Megalopsidiinae, and to further test the hypothesis of Hansen (1997) of the close phylogenetic relationship of Megalopsidiinae with Euaesthetinae and Steninae. Since we are aware of at least three other stem and crown groups relevant for the study of the sister group relationships of these three subfamilies that are currently being studied, we postpone such character analysis until those taxa are named and their formal descriptions are published. Apart from the obvious phylogenetic significance of M. extinctus for rove beetle researchers, its exceptionally well preserved mouthparts showing the same morphological specialization as in recent Megalopinus are important for the reconstruction of the palaeoecology of Megalopsidiinae and understanding rates of evolution of the presumed bradytelic lineages. Acknowledgements We express deep gratitude to Dr. V. Puthz (Burgmuseum Schlitz, Germany) for giving his opinion about our fossil specimen. SY is grateful to Dr. T. Hirowatari (Kyushu University, Fukuoka, Japan) for critically reading and commenting on an earlier version of the _ manuscript, as well both of us acknowledge Dr. D. Zyła (Natural History Museum of Denmark) for her useful comments on the final version. SY also thanks Dr. S. Hosoishi (Kyushu University) for allowing SY to use a microscopic device for our study. Special thanks are also dedicated to Dr. D. Grimaldi (AMNH) for the acquisition of specimen number. We are grateful to two anonymous reviewers who provided helpful comments on the original version of this paper. This study was partially supported by the Grant-inAid for JSPS Fellows (14J02669) to SY from the Japan Society for the Promotion of Science. This is a contribution from the Entomological Laboratory, Faculty of Agriculture, Kyushu University, Fukuoka, Japan (Ser. 7, No. 21). References Benick, L., 1917. Neuer Beitrag zur Kenntnis der Megalopinen und Steninen (Col., Staphyl.). Entomologische Bl€ atter 13 (189e195), 291e314. Benick, L., 1952. Spezielles und Allgemeines über die Subfam. Megalopsidiinae (Col. €fer 47 (1951), Staph.). Entomologische Bl€ atter für Biologie und Systematik der Ka 58e87. Brunke, A., Newton, A.F., Klimaszewski, J., Majka, C., Marshall, S., 2011. Staphylinidae of eastern Canada and adjacent United States. Key to subfamilies; Staphylininae: tribes and subtribes, and species of Staphylinina. Canadian Journal of Arthropod Identification 12, 1e110. http://dx.doi.org/10.3752/cjai.2011.12. Cai, C.-Y., Huang, D., 2013. Mesozoic rove beetles from northeastern China
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