History of Commensal Rodents on Ishigaki Island (Southern Ryukyus) Reconstructed from Holocene Fossils, Including the First Reli
Total Page:16
File Type:pdf, Size:1020Kb
Quaternary International xxx (2015) 1e11 Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint History of commensal rodents on Ishigaki Island (southern Ryukyus) reconstructed from Holocene fossils, including the first reliable fossil record of the house mouse Mus musculus in Japan Ai Kawamura Department of Geosciences, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan article info abstract Article history: The history of commensal rodents in mainland Japan and the Ryukyu Islands (Ryukyus) has been poorly Available online xxx understood owing to the paucity of reliable fossil records. Recent excavation of the Shiraho-Saonetabaru cave site on Ishigaki Island of the southern Ryukyus yielded a large number of rodent fossils from well- Keywords: dated sediments ranging from the Late Pleistocene to the Holocene. Some of the fossils were prelimi- Ishigaki Island narily assigned to Mus musculus and Rattus sp. They are described here to confirm their taxonomic Holocene positions. These forms are considered to be commensal rodents. Commensal rodent A history of commensal rodents on Ishigaki Island is reconstructed based on the stratigraphic position Systematics Fossil and relative abundance of the commensal forms as well as the non-commensal native rodent, Niviventer History sp., which is very abundant in most of the horizons of the sediments. Before the end of the Pleistocene, no commensal forms inhabited the island, and the rodent fauna consisted only of the non-commensal form. In the early Holocene, one of the commensal forms, M. musculus, invaded the island, but the continued abundance of the non-commensal form afterward indicates that the invasion did not affect the fauna. In the late Holocene, a second invasion, by Rattus sp., probably caused the rapid decline and extinction of the non-commensal form. Since the extinction, the rodent fauna of the island has comprised only the commensal forms. In Japan, there are no known reliable fossil occurrences of M. musculus,incontrasttoseveral occurrences of Rattus at Middle Pleistocene to Holocene fossil localities. Thus, the fossil of M. musculus described here records the first reliable occurrence of the species in Japan, and is very important for documenting the first appearance of M. musculus in the southern Ryukyus in the early Holocene. The species is considered to have appeared much later in mainland Japan and the central Ryukyus. © 2015 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction archeologists have paid little attention to Quaternary fossils of these species, and because many allocations of these fossils to Three commensal rodent species (rodents closely associated species have been incorrect. On Ishigaki Island of the Ryukyus with humans) are now distributed all over Japan. They are the (Ryukyu Islands; Fig. 1A), the current rodent fauna comprises only house mouse Mus musculus, the ship or black rat Rattus rattus, and these commensal species, and lacks any non-commensal native common or brown rat Rattus norvegicus, all of which have world- species. The commensal species must have invaded the island wide distributions. The species' histories, based on fossil records, sometime in the Quaternary, and replaced native species now have been obscure in Japan because paleontologists and extinct on the island. Until 2010, however, no reliable fossil records of the commensal species had been known from the island. In 2010, an extensive excavation was carried out at the Shiraho-Saonetabaru cave site on Ishigaki Island (Fig. 1B), because the site had yielded reliably-dated Pleistocene human bones, which had been rare in Japan (Nakagawa et al., 2010). E-mail address: [email protected]. Specifically, the excavation revealed stratigraphic sequences of http://dx.doi.org/10.1016/j.quaint.2015.01.024 1040-6182/© 2015 Elsevier Ltd and INQUA. All rights reserved. Please cite this article in press as: Kawamura, A., History of commensal rodents on Ishigaki Island (southern Ryukyus) reconstructed from Holocene fossils, including the first reliable fossil record of the house mouse Mus musculus in Japan, Quaternary International (2015), http:// dx.doi.org/10.1016/j.quaint.2015.01.024 2 A. Kawamura / Quaternary International xxx (2015) 1e11 Fig. 1. Maps showing (A) the location of Ishigaki Island and the fossil localities in mainland Japan discussed in the text, and (B) the topography of Ishigaki Island and the locations of the fossil localities discussed in the text. the site's sediments, and produced abundant collections of hu- (Fig. 1B). The northern half of the main part is largely moun- man bones, non-human mammal fossils, and artifacts (Nakaza tainous, with the highest peak 525.8 m above sea level, and is et al., 2013). The geological age of the sediments was formed primarily by pre-Neogene basement rocks comprising confirmed to range from the Late Pleistocene to the Holocene by sedimentary, igneous, and metamorphic rocks. The topography a number of radiocarbon dates as well as archeological analyses and geology continue along the peninsula. In contrast, the of the artifacts. southern half of the main part is mostly hills and terraces, and is Among the mammal fossils collected, those of small mam- formed primarily by Pleistocene limestone and clastic sediments, mals were especially abundant, and were preliminarily studied collectively named the Ohama Formation by Nakagawa et al. by Kawamura and Kawamura (2013). Some of the fossils studied (1982). They overlie the basement rocks. The Shiraho- are referable to M. musculus and Rattus sp., and are considered Saonetabaru cave site is located in the northeastern area of the to record the presence of commensal rodents on this island. In southern half, about 0.7 km inland (24 240100N, 124 1404500 E; this paper, detailed systematic descriptions are given to the Fig. 1B). fossils referred to these two forms, to confirm their taxonomic Around this site, long and largely horizontal caves have positions. Using taxonomy and the chronological distributions of developed in the limestone of the Ohama Formation along the all the rodent forms from the site, this paper reconstructs a unconformable boundary between the limestone and meta- history of the commensal rodents on Ishigaki Island, and relates morphic basement rocks, the latter named the Tomuru Forma- it to the extinct native rodent form that was assigned to tion by Foster (1965). The site is situated in one of the caves, Niviventer sp. by Kawamura and Kawamura (2013). Furthermore, called Shiraho-Saonetabaru Cave by Nakagawa et al. (2010). this paper discusses the significance of the M. musculus fossil Yamasaki and Nakazato (2013) inferred that the ceiling of this from the site, the first reliable fossil record of this species in cave had collapsed with the enlargement of the cave, thereby Japan. forming a doline-like depression in which sediments had been continuously deposited from the Late Pleistocene to modern times. 2. Geographical and geological settings The generalized stratigraphic sequence of the sediments is described by Katagiri and Yamasaki (2013), and is outlined in Ishigaki Island is situated in the southwestern part of the Table 1. The sediments are divided into five layers: 0 to IV, in Ryukyu Islands, which form an island arc between Kyushu and descending order. Layers III and IV are subdivided into Layers IIIA Taiwan (Fig. 1A). The island is closer to Taiwan than to Okinawa to IIIE and Z, and Layers IVA and IVB, respectively. Among the Island, the largest central island of the arc. Ishigaki Island consists layers, Layer 0 represents the topmost artificial sediments of of a square-like main part and a northeast-extending peninsula modern times. Layer I is composed of dark brown sandy mud Please cite this article in press as: Kawamura, A., History of commensal rodents on Ishigaki Island (southern Ryukyus) reconstructed from Holocene fossils, including the first reliable fossil record of the house mouse Mus musculus in Japan, Quaternary International (2015), http:// dx.doi.org/10.1016/j.quaint.2015.01.024 not shown in representative of soricomorphs in the fauna of this site, but is from bution of each form and its relative abundance, based on data circle in or comparable to the speciescle now in inhabiting Ishigaki Islandprobably (open became extinct sometime innot the have late comparable Holocene (solid species cir- now inhabiting Ishigakisequence Island, in and bution in the site, and is uncertainrence in of correlationforms, with the sp.), and one isforms a described domestic species andfi ( discussed hereNamiki ( (2013) layers except Layer 0. 3. Faunal setting uncalibrated radiocarbon dates. mainland Japan, respectively,roughly and correspond numerical to the ages 14th toYamasaki represent (2013) 17th centuries, estimated and ranges the cave Heian of to site, Yayoi Periods with in lithology,Generalized geological stratigraphic sequence age, of andTable 1 the the sediments age in estimation the by Shiraho-Saonetabaru dates). tained dates rangingcarbon from method ca. 0.3 usingdated ka a accelerator to number mass ca.Layer of 24 IV spectrometry, samples ka is and fromlimestone (uncalibrated also Layers ob- breccia composed I bed ofsponding to interposed brown to IVB the mud. between Late by Jomonments Layers the Period IIIE in radio- indicative mainland and Japan.brown Layer IVA. of mud. Z Its is the a uppermostorigin. part Layer Shimotabaru III, (L exceptabundant Period fossils its of lowest roughly marine partLayer organisms, (Layer corre- and II Z), is probably is isyielding of composed artifacts tsunami a of of the characteristic Nakamori Period brown (14th sand to 17th centuries). and gravel layer with dx.doi.org/10.1016/j.quaint.2015.01.024 Holocene fossils, including the Please cite this article in press as: Kawamura, A., History of commensal rodents on Ishigaki Island (southern Ryukyus) reconstructed from ve are Holoceneage ModernGeological Layer 0 Arti Late Pleistocene ca.16 Among the 12 forms, Fossils of land mammals including humans occur in all the Table 2 Doi et al.