Historical Biology An International Journal of Paleobiology ISSN: 0891-2963 (Print) 1029-2381 (Online) Journal homepage: https://www.tandfonline.com/loi/ghbi20 The extant telephone-pole beetle genus Micromalthus discovered in mid-Cretaceous amber from northern Myanmar (Coleoptera: Archostemata: Micromalthidae) Shûhei Yamamoto To cite this article: Shûhei Yamamoto (2019): The extant telephone-pole beetle genus Micromalthus discovered in mid-Cretaceous amber from northern Myanmar (Coleoptera: Archostemata: Micromalthidae), Historical Biology, DOI: 10.1080/08912963.2019.1670174 To link to this article: https://doi.org/10.1080/08912963.2019.1670174 Published online: 06 Oct 2019. Submit your article to this journal Article views: 123 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=ghbi20 HISTORICAL BIOLOGY https://doi.org/10.1080/08912963.2019.1670174 ARTICLE The extant telephone-pole beetle genus Micromalthus discovered in mid-Cretaceous amber from northern Myanmar (Coleoptera: Archostemata: Micromalthidae) Shûhei Yamamoto Integrative Research Center, Field Museum of Natural History, Chicago, IL, USA ABSTRACT ARTICLE HISTORY The telephone-pole beetle family Micromalthidae has attracted the attention of entomologists and Received 19 August 2019 biologists because of its enigmatic morphology, systematic position, and complex life cycle. With only Accepted 17 September 2019 a single extant and four extinct species, the micromalthid beetles are a small but important lineage KEYWORDS ff within the primitive suborder Archostemata. Fossil micromathids, known mainly from di erent amber Micromalthus; deposits, are not commonly found. Here, I report the first Mesozoic fossil of the sole extant micro- Micromalthidae; malthid genus Micromalthus in the mid-Cretaceous Kachin amber from northern Myanmar. Due to its Archostemata; Burmese rather poor preservation, this provisional new species remains unnamed, tentatively identified as amber; Cenomanian; fossil Micromalthus sp. The newly found specimen is about 46 Ma older than an Eocene Micromalthus fossil from the Oise amber of France. My study greatly expands our knowledge of the origin and early evolution of Micromalthus beetles. Introduction some specific areas in the world (as summarised in Ruzzier and Colla 2019: Figure 2). The native range is thought to be With nearly 400,000 described species, Coleoptera (beetles) is the eastern part of the USA and possibly also Central America by far the largest order of organisms in terms of species (Philips 2001; Philips and Young 2001). This current wider richness, demonstrating remarkable morphological and eco- distribution of M. debilis is considered to be the result of logical diversity (Crowson 1981; Grimaldi and Engel 2005). human activities, globalisation, and the international timber The majority of this diversity is in Polyphaga, one of the four trade, rather than merely dispersal events (e.g. Ruzzier and suborders of Coleoptera, which accounts for over 90% of all Colla 2019). beetle species. By contrast, Archostemata is a small relict In general appearance, Micromalthus beetles are quite dif- group comprised of four (Lawrence 2016)orfive families ferent from the much more speciose, core archostematan (Hörnschemeyer 2016, including Jurodidae) with only about families Cupedidae and Ommatidae. Nonetheless, the phylo- 40 extant species (Yavorskaya et al. 2018). However, there are genetic affinity of M. debilis with Ommatidae is supported by diverse and abundant fossil records from the Mesozoic for morphological characters (Hörnschemeyer 2009) and mole- this group; thus, it is apparent that the archostematans were cular evidence (McKenna et al. 2015). The adults of M. debilis much more diverse than they are now. The systematic posi- are very small (~2.5 mm), narrowly elongated, and only tion of Archostemata remains unresolved, and morphological weakly sclerotised; they have smooth and shortened elytra, and molecular studies have yielded conflicting results (e.g. and superficially resemble some rove beetles (Staphylinidae) Lawrence et al. 2011; McKenna et al. 2015; Beutel et al. (Paterson 1938; Philips and Young 2001; Yan et al. 2019). The 2019). Nevertheless, it has retained many ancestral features larvae of M. debilis are wood borers that feed on, or develop and constitutes an important subgroup of Coleoptera (e.g. in, decaying oaks, chestnuts, hemlock, and others (Philips and Beutel et al. 2008; Friedrich et al. 2009). Therefore, it is clearly Young 2001; Grimaldi and Engel 2005). M. debilis has the a key taxon for understanding the early evolution of the most complicated and idiosyncratic life cycle of all beetles, mega-diverse beetles (Yan et al. 2019). including thelytoky, arrhenotoky, vivipary, matriphagy, The archostematan family Micromalthidae, or telephone- hypermetamorphosis, and paedogenesis, with several mark- pole beetles, represents a tiny fraction within the suborder edly different larval types (Philips and Young 2001; Pollock Archostemata. In fact, Micromalthus debilis LeConte, 1878 is and Normark 2002; Normark 2013; Hörnschemeyer 2016; the only extant species in this family. Nevertheless, M. debilis Perotti et al. 2016). Micromalthidae (M. debilis) is the only has attracted the attention of entomologists and biologists, family of Coleoptera defined by the presence of haploid mainly because of its unusual, distinct morphology, ancestral males, although such males are found in some bark beetles position, and highly complex life cycle. This species is cur- (Curculionidae: Scolytinae) within Coleoptera (Normark rently distributed globally, but it has been limited only to 2003). CONTACT Shûhei Yamamoto [email protected] Field Museum of Natural History, Integrative Research Center, 1400 S Lake Shore Drive, Chicago, IL 60605, USA © 2019 Informa UK Limited, trading as Taylor & Francis Group Published online 06 Oct 2019 2 S. YAMAMOTO Another interesting feature of M. debilis is that it is a ‘living believed to have been tropical (Grimaldi et al. 2002). It is fossil’; a presumed-extinct Micromalthus species (Perkovsky currently considered that the amber-producing forests were 2007) in the early Middle Miocene Dominican amber (ca. located near a seashore or coastline (Mao et al. 2018;Yu 16 Ma) was later regarded as the same taxon as M. debilis et al. 2019). The beetle inclusions in Kachin amber are (Hörnschemeyer et al. 2010). Like other extant archostematans, remarkably diverse, comprising 207 species in 159 genera the occurrence of M. debilis is rare and sporadic (Philips and and 80 families as of the end of 2018 (Ross 2019). Young 2001; Yavorskaya et al. 2018). Extinct micromalthids The original amber piece was spherical, but the author are also rare in spite of much diverse and abundant taxa of the (SY) later polished the specimen using emery papers differing other extinct archostematan families and also despite its pecu- in grain size and a plastic buffing cloth. This process yielded liar body form, which attracts palaeontologists and entomolo- a thin, flattened amber piece, allowing detailed observations. gists. However, its small size and weak sclerotisation make When it was observed or photographed, the amber was com- fossilisation difficult, particularly with respect to impression pletely submerged in clove oil (Wako Pure Chemical fossils (Yan et al. 2019). All but one micromalthid fossils are Industries, Osaka, Japan; refractive index, 1.52–1.55), to either Cenozoic or Mesozoic amber inclusions, which include avoid extra reflections and improve the visibility of the beetle larval and adult forms in the Middle Miocene Dominican fossil from multiple angles. Observations were made using amber (Lawrence and Newton 1995; Perkovsky 2007; a Leica MZ16 stereomicroscope (Leica Microsystems, Hörnschemeyer et al. 2010), a larval form in the Miocene Wetzlar, Germany). Photographs (Figures 1, 2, 3(e), 4) were Mexican amber (Rozen 1971), larval and adult forms in the taken using an 80D digital camera (Canon, Tokyo, Japan) Upper Eocene Rovno amber (Perkovsky 2016), a larval form in with an MP-E 65 mm macro lens (F2.8, 1–5 ×; Canon) and an the Upper Eocene Baltic amber (Lawrence and Newton 1995), MT-24EX Macro Twin Lite Flash (Canon). Additional photos an adult form in the Lower Eocene Oise amber from France (Figures 3(a–d), 5, 6) were obtained with the Dun Ink BK (Kirejtshuk et al. 2010), and a larval form in the Lower PLUS Lab System (Dun, Palmyra, VA, USA) mounted on Cretaceous Lebanese amber (described as an extinct genus; a 6D digital camera (Canon) with a 10 × lens. The images Kirejtshuk and Azar 2008). Recently, the oldest micromalthid were stacked using the automontage software Helicon Focus fossil was found in the Upper Permian Babiy Kamen’ locality 7.5.4 (Helicon Soft, Kharkiv, Ukraine). All images were edited in Siberia, and was described as a second extinct genus in the and arranged with Photoshop® Elements 15 (Adobe Systems, family (Yan et al. 2019). Consequently, a total of four extinct San Jose, CA, USA). The sole specimen is deposited in the micromalthid species has been described, namely two extinct entomological collection of the Gantz Family Collections Micromalthus species (Perkovsky 2007, 2016; Hörnschemeyer Centre, Field Museum of Natural History (FMNH), Chicago et al. 2010; Kirejtshuk et al. 2010) and two monotypic extinct genera (Kirejtshuk and Azar 2008; Yan et al. 2019). Nevertheless, very little is known about