Discovery, excavation and preparation records of the “Paleopara-doxiid Mizunami-Kamado specimen” from the Shukunohora Formation, Mizunami Group in Mizunami City, central Japan

A platanistoid fossil was recovered from the upper Lower Miocene Akeyo Formation, Mizunami Group, Gifu Prefecture, Japan. It consists of a right scapula, two cervical and three thoracic vertebrae, and an isolated tooth. The following key apomorphies of Platanistoidea are found in the scapula of the specimen: loss of or greatly reduced coracoids process, acromion located on the anterior edge of the scapula, and disappearance of the supraspinatus fossa on the lateral side of the scapula. This is the fourth platanistoid to be reported from Japan.

ABSTRACTA new early Miocene large castorid, Minocastor godai gen. et sp. nov., from the Dota locality, Gifu Prefecture in central Japan, is described on the basis of dentaries and teeth. The material comes from the Kani basin, where limnofluviatile clay and sandstones of the Nakamura Formation (Mizunami Group) are exposed on the southern (left) bank of the Kiso River. It represents the richest sample of a Miocene small mammal in the Japanese fossil record thus far known. Based on jaw and tooth morphology, this new castorid most likely represents a primitive anchitheriomyine. However, it lacks the marked striations on the incisors that are characteristic of the advanced large, middle Miocene anchitheriomyines like Anchitheriomys and Amblycastor. The new castorid shares this dental feature with other primitive anchitheriomyines from Asia and North America, like Propalaeocastor, Oligotheriomys, and Miotheriomys. For these genera, a new tribe, Minocastorini, is proposed as sister group to the Anchitheriomyini. The incisor enamel microstructure of the new castorid largely exhibits plesiomorphic characters but also apomorphic features such as pseudo-pauciserial Hunter-Schreger bands. Additionally, the outer portion of the enamel band is rather thick in comparison to that of other beavers. Based on the rodent taxa associated with Minocastor godai gen. et sp. nov., Dota can be correlated with European Neogene mammal units MN 3/4. Magnetostratigraphic studies and radiometric dates obtained from the Mizunami Group indicate that Dota is more likely correlated with MN 3, with an absolute age of around 18.5 Ma.http://zoobank.org/urn:lsid:zoobank:org:pub:B1886424-1759-4BDA-A5CC-D122436E1A76 Citation for this article: Mörs, T., Y. Tomida, and D. C. Kalthoff. 2016. A new large beaver (Mammalia, Castoridae) from the early Miocene of Japan. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1080720.

Identification of a nearly complete skeleton of a paleoparadoxiid (Mammalia: Desmostylia) from the Lower to Middle Miocene Shukunohora Formation, Mizunami Group in Kamado Town, Mizunami City, central Japan

Molluscan fossils from the locality of the “Paleoparadoxiid Mizunami-Kamado specimen” of the Shukunohora Formation, Mizunami Group in Mizunami City, central Japan

A petrographic study of sandstones from the Miocene Mizunami Group in Central Japan has been performed on core samples from a single borehole, in order to evaluate the provenance of the sedimentary rock. Evaluation of the provenance is based on bulk mineral, heavy mineral and plagioclase contents and on whole rock chemical compositions. The sandstones studied are divisible into three types; the first type is characterized by the occurrence of biotite and plagioclase ranging from albite to oligoclase, the second type is characterized by the dominance of amphibole and labradorite with pyroxene (clinopyroxene > orthopyroxene), and the third type is characterized by the dominance of pyroxene (orthopyroxene > clinopyroxene) and andesine with lesser labradorite, bytownite and anorthite. The first type is interpreted to be derived from the basement granite, whereas the others were derived mostly from volcanic ash, judging from their mineral compositions. The volcanic activity that supplied the volcanic ash to the Mizunami Basin occurred in two phases, distinguishable by variations in their mineralogical and geochemical compositions, an indication of change in character of the volcanic activity. This petrographic study of the sandstones in the Mizunami Group suggests that unrecognized volcanic activity occurred around the Mizunami Basin, even though potential provenance of the volcanic ash has not yet been identified.

Miocene palaeogeography of the Mizunami group of the Tono region, central Japan

Skeleton and taphonomy of the “Paleoparadoxiid Mizunami- Kamado specimen” from the Shukunohora Formation, Mizunami Group in Mizunami City, central Japan

Citation for this article: Handa, N., and S. Kawabe. 2016. Femur of Schizotheriinae (Perissodactyla, Chalicotheriidae) from the lower Miocene Hiramaki Formation of the Mizunami Group in Gifu Prefecture, central Japan. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1131163.

Fossil Ostracoda and Foraminifera from the locality of the “Paleoparadoxiid Mizunami-Kamado specimen” of the Miocene Shukunohora Formation, Mizunami Group, Mizunami City, central Japan

市道戸狩・月吉線工事現場(瑞浪市明世町)の下部中新統瑞浪層群明世層より鰭脚類の頭蓋を含む骨格化石の産出

Fission track (FT) ages were determined for 14 tuff samples from the Miocene Mizunami and Iwamura groups in southeastern Gifu Prefecture, Central Japan. On the basis of FT ages for the Mizunami Group, the Hongo Formation was deposited ca. 17 Ma, and the Akeyo Formation was deposited at ∼17—16 Ma. For the Iwamura Group, the depositional age of the Agi Formation was found to be ca. 20—18 Ma and the lower part of the Toyama Formation was deposited at ∼17—16 Ma. Depositional FT ages for the Akeyo and Toyama formations are almost 1 Myr younger than their fossil ages.

A recently discovered, incomplete dentary with preserved incisor, premolar and first molar of a minute castorid from the Dota locality, Kani Basin, early Miocene (ca. 18.5 Ma) Nakamura Formation of the Mizunami Group in central Japan, is described as a new species of the trogontheriine beaver Euroxenomys. It represents the first record of Euroxenomys in Asia and one of the oldest records of this genus. Euroxenomys nanus sp. nov. is smaller than the type species, E. minutus from the Miocene of Europe and more hypsodont, but similar in size to E. inconnexus from the Barstovian of Montana. Dota is the first Asian locality with three cooccurring castorids, Youngofiber sinensis, Minocastor godai, and E. nanus.

A new species of the genus Amia of the family Amiidae, A. godai is described based on a parasphenoid and many isolated bones and scales found from the Early Miocene Nakamura Formation of the Mizunami Group along the Kiso River in Kani City, Gifu Prefecture, Central Japan. Amia godai sp. nov. is distinguished by having a V-shaped edentulous area in the posterior part of the tooth patch of the parasphenoid. This is the first record of the genus from the Early Miocene in the world and the first record of the family from the Cenozoic in Japan.

A method for estimating paleobathymetric depth from molluscan community structure : A case study in the Miocene Mizunami Group in central Japan

Limnobiophyllum expansum (Lemnoideae, Araceae) was newly found in the lower Miocene (18.4–17.0 Ma) Hiramaki Formation of the Mizunami Group in the Kani Basin, Gifu Prefecture, central Japan. This genus was distributed widely in the Northern Hemisphere from the Late Cretaceous to the Paleocene, but a Miocene descendant (L. expansum) was reported only from Europe, in the Bohemian Basin, Czech Republic (early Miocene), Paldau, Austria (late Miocene), Schrotzburg, Switzerland (late Miocene) and Sośnica, Poland (late Miocene). Our finding is the first record of a Miocene Limnobiophyllum from an area other than Europe. The aquatic flora of Japan during the early Miocene is poorly documented, but this finding suggests a link between the aquatic floras of Europe and Asia.