Abstract Abstract
The first fossil of the staphylinine tribe Diochini Casey is described and figured from an inclusion in mid-Eocene (Lutetian) Baltic amber. Diochus electrus sp. n. is distinguished from its congeners and the diversity of rove beetles (Staphylinidae s.l.) is summarized briefly.
Keywords: Tertiary, Eocene, Lutetian, fossil, Staphylininae, Diochini, taxonomy
Introduction
More so than any other amber deposit in the world, the fossiliferous resin from the blaue Erde of northern Europe has garnered the attention of researchers, artists, and amateurs. For literally millennia Baltic amber has been the focus, if not obsession, of innumerable individuals and as such its included flora and fauna is one of the most completely understood paleoecosystems. Despite this fascination and intense activity, there remains huge swaths of the fauna to revise and newly document. Among those groups requiring significant attention are the beetles of the family Staphylinidae (sensu Bouchard et al. 2011). Most species, largely of the subfamilies Scydmaeninae and Pselaphinae, were described more than a century ago by (Schaufuss (1888, 1890a, 1890b, 1890c, 1892, 1896) and are in need of revision and figuring, should new material eventually be located (vide Appendix). Fortunately, several new works during the last 35 years, particularly the last decade, have added significantly to this fauna and provided a more modern perspective on staphylinid diversity in Baltic amber (vide Appendix). Unfortunately, the diverse subfamily Staphylininae has not been recorded formally since Schaufuss (1888) described Bembicidiodes inaequicollis, a species more recently considered of uncertain subfamilial affinity (Herman 2001).
In this paper we describe the first fossil species of Diochus Erichson from middle Eocene Baltic amber and as the first, definitive fossil staphylinine. The tribe Diochini Casey includes the genera Antarctothius Coiffait and Saiz, Coomania Cameron, and Diochus. The tribe has not received much taxonomic attention and the boundaries between these genera are not clear. Newton (1985) suggested that Antartoctothius might be co-generic with Diochus, which is the genus with the highest number of species (40) in the tribe. Diochus has a worldwide distribution but the majority of species are found in the New and Old World tropics. There are ten species of Diochus in the Palearctic region (Smetana 2004; western Palearctic species revised by Assing 2003) and only one in the Nearctic (Smetana 1982). Smetana (1982) noted that Diochus is in dire need of systematic revision and that it is extremely hard to differentiate between species.
Material and methods
Measurements were made using an ocular micrometer on an Olympus SZX-12 stereomicroscope and all measurements refer to maximum width or length of a particular structure. Total length is measured from the anterior margin of the clypeus to the posterior margin of abdominal segment VIII. Due to the placement of the fossil in amber, not all typical measurements were possible. Photomicrographs where prepared with a Nikon D1x digital camera attached to an Infinity K-2 long-distance microscope lens.
The age, origin, and biotic diversity of Baltic amber has recently been summarized by Weitschat and Wichard (2010). Material discussed herein is deposited in the Fossil Insect Collection of the Division of Entomology, University of Kansas Natural History Museum, Lawrence, Kansas, USA.
Systematic placement
The fossil is placed in the tribe Diochini (and the genus Diochus) based on the following characters (from Smetana 1982): antennae not geniculate; maxillary palpus (P2 and P3) finely pubescent; neck narrow, only about a forth as wide as head and frons between antennal insertions truncate. The direct comparison of the fossil described here with Coomania was not possible due to the lack of Coomania specimens, however, in the published description of Coomania (Cameron 1939) the neck is much narrower than in Diochus, only a fifth as broad as the head.
Systematic paleontology
Family Staphylinidae Latreille, 1802
Subfamily Staphylininae Latreille, 1802
Tribe Diochini Casey, 1906
Genus Diochus Erichson, 1839
Diochus electrus
Chatzimanolis & Engel sp. n.
urn:lsid:zoobank.org:act:C24A1C8A-B27B-48EC-8100-2FE43C4913E6
http://species-id.net/wiki/Diochus_electrus
Figures 1–3.
Photomicrographs of holotype female of Diochus electrus Chatzimanolis & Engel, sp. n. (B-244). 1 Dorsal view 2 Details of head 3 Details of abdominal apex.
Holotype.
♀; KU-NHM-ENT, B-244 (Fig. 1); with labels: “Amber: Baltic, middle Eocene (Lutetian), blaue Erde, Northern Europe, KU-NHM-ENT-B244” // “HOLOTYPE Diochus electrus Chatzimanolis and Engel, des. Chatzimanolis and Engel 2011”. Deposited in Fossil Insect Collection, Division of Entomology, University of Kansas Natural History Museum, Lawrence.
Diagnosis.
Diochus electrus can be distinguished from otherwestern Palearctic species of the genus by the differences in the relative proportion of elytra to pronotum (elytra longer than pronotum in Diochus electrus; shorter than elytra in other species) and the proportions of the head (head much more elongate in the extant species than in Diochus electrus).
Description.
Total length 3.5 mm; body coloration brown to black except antennae somewhat orange and abdominal segment VIII light brown. Head ovoid, length 0.56 mm, width 0.48 mm, slightly longer than wide (Fig. 2); compound eye length 0.18 mm, postoccular region convex, about twice as long as compound eyes; head with large macrosetae near posterior margin; head with transverse microsculpture and sparse small punctures. Antennomeres 1–5 longer than wide; antennomeres 6–10 subquadrate, antennomere 11 longer than wide; antennomere 1 as long as twice length of antennomere 2; antennomere 3 1.5 times longer than antennomere 2; antennomere 4 slightly shorter than antennomere 3; antennomere 5 slightly shorter than antennomere 4; antennomeres 6–9 subequal in length; antennomere 10 slightly longer than previous antennomeres but shorter than antennomere 11. Mouthparts not visible except right maxillary palp; maxillary palpomere I (P1) not visible, P2 longer than wide, club-like, about as long as P3; P3becoming wider distally; P4 extremely small, slender, conical, about seven times smaller than P3. Pronotum subquadrate, wider than head; pronotal length 0.64 mm, width 0.49 mm; anterolateral corners curved ventrally and not visible from above; pronotum smooth with sparsely scattered small, shallow punctures.Elytra longer than pronotum; elytra length 0.75 mm, elytra width 0.67 mm; elytra with dense macrosetae, expanding posteriorly; elytra sculptured as on pronotum. Legs (forelegs not visible) with slender tibiaecovered in long spurs distally; tarsi elongate, metatarsi almost as long as metatibia; metatarsomeres I and II greatly expanded. Abdomen with dense macrosetae (Figs 1, 3); segment VI longer than preceding segments; segment VII about twice as long as segment V; sternum VIII without any secondary sexual structures.
Etymology.
The specific epithet is an adjective derived from the Latin noun for amber (electrum).
Supplementary Material
Acknowledgements
We thank two anonymous reviewers and the editor for comments that improved this manuscript. Financial support was provided by US National Science Foundation grant DEB-0741475 (to S.C. and M.S.E.).
Appendix
Checklist of described Baltic (including Bitterfeld and Rovno) amber Staphylinidaearranged by subfamily (sensu Bouchard et al. 2011); older records also exist for the subfamilies Euaesthetinae, Micropeplinae, Osoriinae, Oxytelinae, Phloecharinae, Proteininae, and Scaphidiinae but based on unidentified or undescribed material (e.g., Klebs 1910; Larsson 1978; Spahr 1981, Puthz 2006, 2008).
Subfamily Aleocharinae Fleming
Adinopsis groehni Zerche, 1999
Aleochara (Aleochara) baltica Paśnik & Kubisz, 2002
Atheta (Datomicra) jantarica Paśnik, 2005
Baltioligota electrica Paśnik, 2005
Dictyon antiquus Paśnik & Kubisz, 2002
Electrogymnusa baltica Wolf-Schwenniger, 2004
Leptusa (Protoleptusa) defuncta Semenov et al. 2001 [Rovno]
Phymatura electrica Paśnik & Kubisz, 2002
Subfamily Omaliinae MacLeay
Pseudolesteua insinuans Schaufuss, 1890b
Subfamily Oxyporinae Fleming
Oxyporus blumenbachii Gravenhorst, 1806
Subfamily Paederinae Fleming
Lathrobium ambricum Paśnik & Kubisz, 2002
Lathrobium balticum Paśnik & Kubisz, 2002
Lathrobium jantaricum Paśnik & Kubisz, 2002
Lathrobium succini Paśnik & Kubisz, 2002
Lathrobium (Palaeolobrathium) whitei Abdullah & Abdullah, 1968
Subfamily Pselaphinae Latreille
Barybryaxis lata Schaufuss, 1890a
Batrisus antiquus Schaufuss, 1890a
Batrisus pristinus Schaufuss, 1890a
Bythinus foveopunctatus Schaufuss, 1890a
Bythinus schaufussi Reitter, 1891 (nom. n. proB. caviceps Schaufuss, 1890a)
Bythinus tenuipes Schaufuss, 1890a
Bythinus typicus Schaufuss, 1890a
Ctenistodes claviger Schaufuss, 1890a
Cymbalizon tyroides Schaufuss, 1890a
Dantiscanus costalis Schaufuss, 1890a
Deuterotyrus redivivus Schaufuss, 1890a
Euplectus lentiferus Schaufuss, 1890a
Euplectus mozarti Schaufuss, 1890a
Euplectus quadrifoveatus Schaufuss, 1890a
Euspinoides glabrellus Motschulsky, 1856
Faronus porrectus Schaufuss, 1890a
Faronus tritomicrus Schaufuss, 1890a
Greys conciliator Schaufuss, 1890a
Hagnometopias pater Schaufuss, 1890a
Hetereuplectus retrorsus Schaufuss, 1890a
Monyx spiculatus Schaufuss, 1890a
Nugaculus calcitrans Schaufuss, 1890a
Nugator stricticollis Schaufuss, 1890a
Pammiges spectrum Schaufuss, 1890a
Pantobatrisus cursor Schaufuss, 1890a
Rybaxis glabrella (Schaufuss, 1890a)
Rybaxis patris (Schaufuss, 1892)
Rybaxis veterum (Schaufuss, 1890a)
Tmesiphoroides cariniger Motschulsky, 1856
Tychus avus Schaufuss, 1890a
Tychus radians Schaufuss, 1890a
Tyrus electricus Schaufuss, 1890a
Subfamily Scydmaeninae Leach
Aenictosoma doenitzi Schaufuss, 1892
Clidicus balticus Schaufuss, 1896
Cryptodiodon corticaroides Schaufuss, 1890c
Electroscydmaenus pterostichoides Schaufuss, 1890c
Euconnus fossilis Franz, 1976
Euconnus liedtkei Franz, 1976
Euconnus sucini Franz, 1976
Euconnus wunderlichi Franz, 1983
Hetereuthia elegans Schaufuss, 1890c
Heuretus coriaceus Schaufuss, 1890c
Neuraphes fossilis Franz, 1983
Palaeomastigus helmi Schaufuss, 1890c
Palaeothia tenuitarsis Schaufuss, 1890c
Scydmaenoides nigrascens Motschulsky, 1856
Semnodioceras halticaeforme Schaufuss, 1890c
Stenichnus (Cyrtoscydmus) capucinus (Schaufuss, 1890c)
Stenichnus (Cyrtoscydmus) carinulatus (Schaufuss, 1890c)
Stenichnus (Cyrtoscydmus) laticlavus (Schaufuss, 1890c)
Stenichnus (Cyrtoscydmus) titubans (Schaufuss, 1890c)
Subfamily Staphylininae Latreille
Bembicidiodes inaequicollis Schaufuss, 1888 (subfamily questioned: Herman 2001)
Diochus electrus Chatzimanolis & Engel, sp. n.
Subfamily Steninae MacLeay
Stenus (Hemistenus) priscus Benick, 1943
Stenus abraham Puthz, 2010
Stenus archetypus Puthz, 2010
Stenus atavus Puthz, 2010
Stenus avus Puthz, 2010
Stenus groehni Puthz, 2010
Stenus ketura Puthz, 2010
Stenus methusalem Puthz, 2010
Stenus noach Puthz, 2010
Subfamily Tachyporinae MacLeay
Bolitobius groehni Schülke, 2000
Palaeosepedophilus succinicus Paśnik & Kubisz, 2002
Sepedophilus balticus Paśnik & Kubisz, 2002
Tachyporus bicoloratus Paśnik, 2005
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