第 四 紀 研 究(The Quaternary Research) 37 (2) p. 117-129 May 1998 Early Pleistocene Ground Beetles (Coleoptera: Carabidae) from the Ookui Formation in Nagano Prefecture, Central Japan, and their Biogeographical and Paleoenvironmental Significance Masakazu Hayashi* Abundant fossil beetles were obtained from the Lower Pleistocene Ookui Forma- tion in Kitamimaki-mura, Kitasaku-gun, Nagano Prefecture, Central Japan. These fossils are composed of ground and aquatic beetles, such as Carabidae, Dytiscidae, Hydrophilidae, and Donaciinae of Chrysomelidae. Several fossils of ground beetles are identified with three interesting species, Hemicarabus maeander, Apotomopterus maacki, and Chlaenius gebleri. Among them, H. maeander is not distributed in Honshu where the fossil occurred, but can be found in Hokkaido, Chejudo, Sakhalin, N. E. China, Mongolia, East Siberia, and North America at the present time. The fossil finding indicates that the widely and continuous distributional range of this species seemed to become discontinuous, and extinct in Honshu after the Early Pleistocene. Thus, this species can be considered as a geographic relict species in Honshu during the Pleistocene. The paleoenvironment of the Upper member of the Ookui Formation based on beetle fossils seems that there were mainly low moor of reeds accompanied with areas of still water. These beetle assemblages, especially including H. maeander and C. gebleri, suggest presence of low moor which is similar to those found in Hokkaido during the Upper member of the Ookui Formation deposited. Key Words: Biogeography, carabid beetles, Early Pleistocene, geographical relic, Hemicarabus maeander, Ookui Formation fossil records of carabid beetle from Japan are I. Introduction poorly known. Ground beetles belonging to the family Car- The author investigated the Early Pleis- abidae of Coleoptera live in various ground tocene insect fossils from the Ookui Formation environments. Carabid beetles of subfamily in Kitamimaki-mura, Kitasaku-gun, Nagano Carabinae, especially genus Carabus possess Prefecture, Central Japan. These insect fossils remarkable geographic variation, and have include several interesting species of ground poor dispersal ability because they lack func- beetles. In this paper, I described fossil speci- tional hind wings. Therefore, many hypotheses mens of these species, and discussed their of origin, composition, and differentiation of biogeographical and paleoenvironmental signif- the present Japanese fauna of the subfamily icance. Carabinae, based on their distribution and II. Geological setting phylogenetic relations, have been proposed (e. g. Hiura,1965; Ishikawa, 1988, 1989). However, The Ookui Formation is distributed in north- these hypotheses include no fossil data, because ern to eastern marginal part (along the Chi- Received July 3, 1997. Accepted March 14, 1998. * Graduate School of Science and Technology , Niigata University. 8050 Ninomachi, Ikarashi, Niigata, 950-2181. 118 Masakazu Hayashi May 1998 kuma River) and western part of the Komoro the Ookui Formation and the Lowest Forma- Collapse Basin, and belonging to the Plio- tion of the Yachiho Group (Fossil Elephant Pleistocene Komoro Group (Yamagishi and Research Group, 1973; Koizumi and Kitami- Kosaka, 1991). This Formation has a conform- maki-mura Akebonozou Excavation Research able relationship with the overlying Nunobiki- Group, 1995). kannon Formation (Yamagishi and Kosaka, III. Fossil locality and stratigraphic 1991). This Formation is divided into the Lower horizon and Upper members (Iijima et al., 1956), and the deposits containing the fossil locality corre- Fossils of ground beetles were obtained from sponds to the Upper member in the type area. the Upper member of the Ookui Formation at The Upper member of the Ookui Formation riverbed of the Chikuma River in Hakeyama, corresponds to the Lowest Formation of the Kitamimaki-mura, Kitasaku-gun, Nagano Pre- Yachiho Group (Research Group for Mt. North fecture (36°20'32" N; 138°20'35" E: Fig. 1). Yatsugatake, 1988). Deposits of the Hakeyama route are mainly The age of the Upper member of the Ookui composed of alternating sand and silt inter- Formation assigned to Early Pleistocene is calated with gravel and tuff beds. The same based on usefull information as follows: (1) K stratigraphic horizon of the Hakeyama route is -Ar age of the Nunobikikannon Formation exposed in the Nunoshita route, situated about shows 1.4±0.6 Ma (Yamagishi and Kosaka, two kilometers up the river. The both strata of 1991). (2) K-Ar age of the Uppermost Forma- the Hakeyama and Nunoshita routes are inter- tion of the Yachiho Group shows 1.17±0.05 Ma beded in the Hakeyama tuff (Nagamori and (Kaneoka and Kawachi, 1983). (3) The Lowest Kitamimaki-mura Akebonozou Excavation Formation of the Yachiho Group is correlated Research Group, 1995) and the river terrace with the Matuyama Reversed Epoch older than deposit of the Chikuma River unconformably Jaramillo event, based on paleomagnitization covers the Ookui Formation. of volcanic rocks (Kondo, 1988). (4) Fossils of The fossil horizon, situated 70 centimeter Stegodon aurorae reported the Upper member of below the Hakeyama tuff, consists of poorly Fig. 1 Map showing the locality, Hakeyama (×), Kitamimaki-mura Using the topographic map "Veda", scale 1: 25,000 by the Geographical Survey Institute. 1998年5月 Early Pleistocene ground beetles from the Ookui Formation 119 Table 1 Fossils of beetle from the Ookui Formation IV. Fossil beetles from the Ookui Formation Fossil beetles obtained from the locality, are composed of 16 species in five families (Table 1). Modes of occurrence of fossil beetles are characterized by separate of fragmentary exo- skeleton. Fig. 2 Columnar sections at Hakeyama and The fossil assemblages are occupied by Nunoshita routes ground and aquatic beetles. Ground beetles are identified as A potomopterus maaccki, Hemica- sorted muddy sand and gravel (Fig. 2). This rabus maeander, Chlaenius gebleri, Pterostichus horizon yields disarticulated skeleton of sp. cf. P. planicollis etc. Aquatic beetles include Stegodon aurorae (Koizumi and Kitamimaki- Dytiscidae, Hydrophilidae, Donaciinae of Chry- mura Akebonozou Excavation Research somelidae, and others are Curculionidae. Group, 1995). Many hollows are observed at V. Description of some fossil several horizons and can be considered as foot- specimens prints of S. aurorae (Nagamori and Kita- mimaki-mura Akebonozou Excavation Re- Order Coleoptera search Group, 1995). Family Carabidae Subfamily Carabinae 120 Masakazu Hayashi May 1998 Table 2 A list of living specimens the author examined Genus Apotomopterus Hope Apotomopterus maacki (Morawitz) (Plate I-C) Material: Left elytron (basal area) [OMF・ 970314・001]. (collection of the OMNH: Osaka Museum of Natural History, Nagai Park 1-23, Higashisumiyoshi-ku, Osaka, 546-0034, Japan) Description: Elytron entirely black, more or less greenish. Sutural and basal margin nitid; primary intervals colliculate; secondary inter- vals swollen and shiny; tertiary intervals indis- tinct, irregularly granulate ; anterolateral mar- gin not dentate. Measurements: Left elytron [OMF・970314・ 001]. Length 8.4mm+, Width 4.0mm. Comparisons: Specimen of this species can not Fig. 3 Fossil of Hemicarabus maeander from be distinguished from living specimens in exter- the Ookui Formation nal morphology, but smaller than general size in elvtra. Remarks: This specimen is identified with A. maacki on the basis of two swollen secondary Genus Hemicarabus Gehin intervals. Hemicarabus maeander (Fischer) Specimens examined: Ten living specimens (Figs. 3-a, b, Plate I-A, B) from Japan were examined (Table 2). Materials: Left elytron (basal to middle area) Fossil records: In Japan, fossils of A. maacki [OMF・940632・001]. Right elytron (apical area) have not been reported from any other forma- [OMF・950632・001]. (OMNH) tions yet. Description: Elytra entirely metallic green or 1998年5月 Early Pleistocene ground beetles from the Ookui Formation 121 greenish yellow, primary and secondary inter- Material: Pronotum [OMF・951106・001] vals black. Sutural and lateral margin nitid; (OMNH) primary intervals swollen acinose; secondary Description: Pronotum entirely metallic black. intervals swollen, but apical area indistinct; General outline more or less trapezoid; lateral tertiary intervals indistinct, irregularly granu- margin entirely rounded, narrowed towards late; all intervals with microsculpture; anter- front; front and hind margin paralle; median olateral margin finely dentate. line fine; basal fovea and lateral parts coarsely Measurements: punctate, and others shiny but sparsely pun- Left elytron [OMF・940632・001]. Length 6.9 ctate. mm+, Width 3.0mm. ]Measurements: Pronotum [OMF・951106・001] Righte lytron [OMF・950632・001]. Length Length 3.0mm, Width 4.0mm, L: W ratio 0.65. 7.3mm+, Width 3.9mm. Comparisons: Specimen of this species can not Comparisons: Specimens of this species can not be distinguished from living specimens in exter- be distinguished from living specimens in exter- nal morphology, but smaller than general size in nal morphology, but fossils possess no coppery pronotum. red coloration. Remarks: This specimen is identified with C. Remarks: These specimens are identified with gebleri on the basis of trapezoid-shaped prono- on the basis of finely dentate anterolateral tum. margin of elytron (Fig. 3-a). Coloration of fos- Specimens examined: Sixteen living specimens sil specimens were considered to have been from Japan were examined (Table 2). changed by fossilization.