Stuttgarter Beiträge zur Naturkunde

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Stuttgarter Beiträge zur Naturkunde
Serie B (Geologie und Paläontologie)
Herausgeber:
Staatliches Museum für Naturkunde, Rosenstein 1, D-70191 Stuttgart
Stuttgarter Beitr. Naturk.
Ser. B
Nr. 345
6 pp., 3 figs.
Stuttgart, 15. 4. 2004
A new fossil staphylinid genus and species from
Baltic amber (Coleoptera, Staphylinidae,
Aleocharinae, Gymnusini)
KARIN WOLF-SCHWENNINGER
Abstract
A new extinct genus and species, Electrogymnusa baltica (Coleoptera, Staphylinidae, Aleocharinae, Gymnusini), from Baltic amber is described. Electrogymnusa differs from all extant
species of the tribe Gymnusini in body size, length and shape of labrum, length proportion of
first and second antennal segments and in having prominent abdominal setae.
Keywords : Staphylinidae, Aleocharinae, Gymnusini, new genus, new species, Eocene,
Baltic amber.
Zusammenfassung
Eine neue ausgestorbene Gattung und Art, Electrogymnusa baltica (Coleoptera, Staphylinidae, Aleocharinae, Gymnusini), wird aus dem Baltischen Bernstein beschrieben. Electrogymnusa unterscheidet sich von allen rezenten Arten des Tribus Gymnusini durch die Körpergröße, Länge und Form des Labrums, Längenproportion der ersten beiden Antennenglieder und durch die Beborstung des Abdomens.
1. Introduction
Up-to-date ten extant species of the genus Gymnusa are described, some of which
may be distinguished only by the structure of the male copulatory organ (KLIMASZEWSKI 1979, NAOMI 1994), but no description of extinct members of the tribe
Gymnusini from amber existed until now. Recently a new species of the sister group
Deinopsini, Adinopsis groehni, was described from Baltic amber (ZERCHE 1999).
In the amber collection of the Staatliches Museum für Naturkunde Stuttgart
(SMNS) there is a specimen, which can be assigned to the tribe Gymnusini based on
the following characters (KLIMASZEWSKI 1979): elongated labrum, protruding
mouthparts, dorsum of head with 6 setigerous pores, all tarsi 5-segmented, tibia with
irregularly distributed stout spines (Fig. 1).
This beetle is well-preserved but an extensive part of the body is covered with a
white cloudy material, consisting of micro-bubbles (“Verlumung”) which is fre-
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quently found in Baltic amber inclusions. Though several important diagnostic features cannot be identified, the specimen is described, because it seems to be an interesting extinct species in respect of aleocharine phylogeny.
Acknowledgements
I am very grateful to the following persons: ISTVAN ACSAI (Dipperz) for donating the amber specimen to the SMNS, Dr. CHRISTIAN NEUMANN (Museum für Naturkunde Berlin) for
loaning two specimens from the collection BERENDT, Dr. ALEXANDER G. KIREJTSHUK (Zoological Institute, Russian Academy of Sciences, St. Petersburg) for loan of Gymnusa inexspectata paratype, BRIAN L. BEATTY (Snow Entomology Collection, University of Kansas Natural History Museum) for loan of Gymnusa grandiceps holotype, Dr. GÜNTER BECHLY and JOHANNES REIBNITZ (SMNS) for making digital photographs, Dr. GÜNTER BECHLY (SMNS) and
Dr. VOLKER ASSING (Hannover) for critically reading the manuscript.
2. Systematic palaeontology
Order Coleoptera LINNAEUS, 1758
Family Staphylinidae LATREILLE, 1802
Subfamily Aleocharinae FLEMING, 1821
Tribe Gymnusini HEER, 1839
Genus Electrogymnusa n. gen.
Type species: Electrogymnusa baltica n. sp.
Etymology: The generic name Electrogymnusa is formed from “elektron”, the Greek
word for amber, and Gymnusa.
Diagnosis: – This extinct genus resembles the extant genus Gymnusa, from
which it can be distinguished by the following diagnostic features: size somewhat
larger, about 7 mm (incl. head), compared to 4.2–6.5 mm in Gymnusa (KLIMASZEWSKI 1979); elongated labrum, 1.3 times longer than wide, narrowly rounded (only
0.6–0.8 times as long as wide and broadly rounded in Gymnusa, Fig. 2 A, B, C); labial palpi and glossae remarkably longer, widely protruding beyond the labrum;
length of antennal segments I and II at a ratio of about 1.7:1 (max. 1.5:1 in Gymnusa),
abdomen with prominent setae (Fig. 3) (no prominent abdominal setae in Gymnusa).
The monotypic extant genus Stylogymnusa HAMMOND differs from the fossil by
smaller body size (3.8–4.6 mm), a more elongated (twice as long as wide) and apically pointed labrum, a shorter antennal segment I (only 1.4 times as long as segment II)
and the lack of prominent abdominal setae (see HAMMOND 1975). Moreover the anterior tibiae of Stylogymnusa are characterised by a pre-apical ctenidium in a deep
excavation, whereas the ctenidium of both Gymnusa and the fossil genus is in a shallower depression.
Electrogymnusa baltica n. sp.
Figs. 1, 2C, 3
Holotype: Specimen no. SMNS BB-2380 in the amber collection of the Staatliches Museum für Naturkunde Stuttgart, Germany; donation from ISTVAN ACSAI, Dipperz.
Paratypes: two specimens in the amber collection of the Museum für Naturkunde Berlin
(coll. number MB.I.2256 a+b).
Type locality: Baltic
Type horizon and age: Baltic amber, Lower Eocene (40–50 my bp)
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Fig. 1. Electrogymnusa baltica n. gen. n. sp., holotype (SMNS BB-2380, amber collection of
the Staatliches Museum für Naturkunde Stuttgart) (photo BECHLY). Scale: 1 mm.
Fig. 2. Head in frontal view of A: Gymnusa grandiceps CASEY, holotype (Snow Entomology
Collection, University of Kansas Natural History Museum), B: Gymnusa inexspectata KLIMASZEWSKI, paratype (Zoological Institute, Russian Acad. Sci., St. Petersburg) and C: Electrogymnusa baltica n. gen. n. sp., holotype (SMNS BB-2380) (photos REIBNITZ). Scale: 0.5 mm.
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Etymology: The species name baltica refers to the origin from Baltic amber.
Diagnosis: – Electrogymnusa baltica is distinguished from the species of Gymnusa and Stylogymnusa by the characters of the genus.
Description: – Body length (anterior margin of pronotum to abdominal apex)
6.3 mm. Head with 6 setigerous pores which are arranged as in Gymnusa: 3 on each
side of the vertex (one above antennal insertion, one at internal margin of the eye,
and one behind eye). Size of eyes is not measurable (due to turbid deposit, i. e. “Verlumung”). Labrum elongated, 0.44 mm long and 0.34 mm wide and narrowly rounded at apex. Labial palpi and glossae widely protruding beyond the labrum. Segment
I of maxillary palpus inconspicuous, segments II and III apparently subequal in
length and each about 1.25 times as long as antennal segment I. Filiform antenna
with 11 segments, all segments longer than wide, segment I about 1.7 times as long
as segment II. As a result of the “Verlumung” it is not possible to ascertain if there is
an emargination of the outer posterior angle of the elytra and a pectination at the
posterior margin of abdominal segments III–VI. Abdomen pubescent with prominent setae. Tarsomere I of all legs longer than tarsomeres II and III combined.
Two fossil inclusions from the amber collections of the Museum für Naturkunde
Berlin were also examined. These specimens were originally in the collection
BERENDT and have been deposited in the Berlin museum since 1873. Because of their
poor condition (the amber is darkened and the surface is cracked open) it is not possible to prepare proper photographs or drawings. One specimen is labelled as
“Gymnusa proboscoidea” (unpublished designation by SCRIBA or KIESENWETTER,
see HIEKE & PIETRZENIUK 1984), both are identified as Gymnusa sp. by UHLIG 1983.
They are affected by a more ore less strong “Verlumung” on the abdomen or on head
and thorax. One inclusion shows a uniform pectination of the posterior margins of
tergites I–IV and an emargination of the outer posterior angle of the right elytron.
Both specimens share the following characters with the holotype: body size large
(7–8 mm), abdomen with prominent setae (even though less visible than in the holotype) and strongly elongated mouth parts, i. e. distance from antennal insertion to
apical margin of labrum about 0.95 mm (only 0.64 mm on average in extant Gymnusa spp.). The unpublished species name “proboscoidea” refers to this unusual feature within the genus Gymnusa, which already had been recognized by SCRIBA or
KIESENWETTER. Antennal segment I seems to be fairly longer than antennal segment
II but as a result of the poor preservation measurements are not possible.
Due to the similarities with the holotype the specimens from the Museum für
Naturkunde Berlin are considered as paratypes.
Discussion: – Unlike that of any extant Gymnusa species the labrum of the fossil holotype is elongated. It is 1.3 times as long as wide, whereas the labrum of the
compared Gymnusa species is transverse. There is only one member of extant Gymnusini, Stylogymnusa subantarctica HAMMOND, which has an elongated labrum. But
the labrum of Stylogymnusa is distinctly longer (twice as long as wide) than in Electrogymnusa and has another shape (pointed apex).
While all extant species of Gymnusa are distributed in the Holarctic regions, Stylogymnusa subantarctica is endemic to the Auckland Islands and is considered as the
most primitive member of the Gymnusini (HAMMOND 1975). LESCHEN et al. (2002)
argue that Stylogymnusa subantarctica, like Baeostethus chiltoni BROUN, another
Subantarctic aleocharine beetle, is a Pangean relic. While this species appears to have
remained phylogenetically conservative on the Auckland Isles, the other members of
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Fig. 3. Electrogymnusa baltica n. gen. n. sp., holotype (SMNS BB-2380), abdomen with
prominent setae (photo REIBNITZ). Scale: 0.5 mm.
Gymnusini (and the Deinopsini) have been subject to considerable evolutionary
change.
ASHE (2000) studied the mouthparts of Stylogymnusa subantarctica and analysed
the phylogenetic position of this genus. He found only weak evidence for a sister
group relationship between Gymnusa and Stylogymnusa but hypothesized a monophyletic lineage consisting of Stylogymnusa, Gymnusa and the Deinopsini. As the
mouthpart structure of amber inclusions cannot be analysed it is not possible to carry out comparisons with ASHE’s descriptions.
The antennal segment I of the fossil specimen is remarkably long (ratio of lengths
of antennal segments I and II about 1.7:1). In Stylogymnusa, the length of antennal
segment I is about 1.4 times as long as segment II (HAMMOND 1975). Except for
Gymnusa grandiceps CASEY, in which the length of antennal segment I is about 1.5
times as long as segment II, in all extant Gymnusa species the antennal segments I
and II are almost subequal in length. According to the phylogenetic tree of KLIMASZEWSKI (1979), Gymnusa grandiceps represents the most basal species in the
genus Gymnusa.
Electrogymnusa baltica is the first fossil record of a representative of the tribe
Gymnusini. The species demonstrates that the gymnusine staphylinids have a minimum age of 40 to 50 million years. Based on the above-mentioned characters there is
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evidence suggesting that this amber fossil takes an ancestral position in the evolution
of the tribe Gymnusini.
All extant species of the tribe Gymnusini are associated with swampy or shore
habitats (KLIMASZEWSKI 1979). From the frequent occurrence of aquatic insects (e. g.
Scirtidae) in Baltic amber it is known that the Tertiary amber forests were rich in
streams and standing water bodies (WEITSCHAT & WICHARD 1998). Thus we may assume that Electrogymnusa baltica, like the extant species, lived in wet habitats.
3. References
ASHE, J. S. (2000): Mouthpart structure of Stylogymnusa subantarctica HAMMOND, 1975
(Coleoptera: Staphylinidae: Aleocharinae) with a reanalysis of the phylogenetic position of the genus. – Zoological Journal of the Linnean Society, 130: 471–498; London.
HAMMOND, P. (1975): The phylogeny of a remarkable new genus and species of gymnusine
staphylinid (Coleoptera) from the Auckland Islands. – Journal of Entomology, Series
B, 44: 153–173; London.
HIEKE, F. & PIETRZENIUK, E. (1984): Die Bernstein-Käfer des Museums für Naturkunde,
Berlin (Insecta, Coleoptera). – Mitteilungen aus dem Zoologischen Museum Berlin, 60:
297–326; Berlin.
KLIMASZEWSKI, J. (1979): A revision of the Gymnusini and Deinopsini of the world. – Agriculture Canada Monograph, 25: 169 pp.; Ottawa.
LESCHEN, R. A. B., BULLIANS, M. S., MICHAUX, B. & AHN, K.-J. (2002): Systematics of
Baeostethus chiltoni, a subantarctic liparocephaline (Coleoptera: Staphylinidae: Aleocharinae): a Pangean relic or a more recent immigrant? – Journal of the Royal Society
of New Zealand, 32: 189–201; Wellington.
NAOMI, S.-I. (1994): Description of a new species of genus Gymnusa GRAVENHORST
(Coleoptera: Staphylinidae) from Hokkaido, Japan. – Natural History Research, 3:
47–50; Chiba.
WEITSCHAT, W. & WICHARD, W. (1998): Atlas der Pflanzen und Tiere im Baltischen Bernstein.
256 pp.; München (Verlag Dr. Friedrich Pfeil).
ZERCHE, L. (1999): Eine neue Art der Gattung Adinopsis CAMERON aus dem Baltischen Bernstein (Coleoptera: Staphylinidae, Aleocharinae, Deinopsini). – Beiträge zur Entomologie, 49: 97–105; Berlin.
Address of the author:
Dr. Karin Wolf-Schwenninger, Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1,
70191 Stuttgart, Germany.
E-Mail: [email protected]
Manuscript received: 9. 12. 2003, accepted: 18. 2. 2004.
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ISSN 0341-0153
Autoren-Richtlinien: http://www.naturkundemuseum-bw.de/stuttgart/schriften
Schriftleitung: Dr. Ronald Böttcher, Rosenstein 1, 70191 Stuttgart
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