New and Mesozoic-relict mollusks from Paleocene wood-fall communities in Urahoro Town, eastern Hokkaido, northern Japan

Abstract

AbstractFive species of bivalves and two species of gastropods are described from late Selandian to earliest Thanetian wood-fall communities from the Katsuhira Formation in Urahoro Town, eastern Hokkaido, northern Japan. Three bivalves and two gastropods are new to science:Thyasira(Thyasira)oliveriAmano and Jenkins, new species,Astarte(Astarte)paleocenicaAmano and Jenkins, new species,Poromya katsuhiraensisAmano and Jenkins, new species,Neverita majimaiAmano and Jenkins, new species, andBiplica paleocenicaAmano and Jenkins, new species.Poromya katsuhiraensisn. sp. andNeverita majimain. sp. are the earliest records of their genus.Astarte paleocenican. sp. is the last species before the genus disappeared from the northern Pacific region during the Eocene, only to reappear with the opening of the Bering Strait during the latest Miocene. Moreover, two bivalve species and one gastropod genus are Cretaceous relict forms:Propeamussium yubarense(Yabe and Nagao, 1928),Myrtea ezoensis(Nagao, 1938), andBiplicaPopenoe, 1957. These species and other relict protobranch bivalves had wide geographical ranges in the deep sea during the Cretaceous, which helped them to survive the end-Cretaceous mass extinction. The chemosynthesis-based speciesBathyacmaea? sp.,Myrtea ezoensis, andThyasira oliverin. sp. were recovered, but small bathymodioline mussels have not been found. This confirms that the small deep-sea mussels did not appear in the wood-fall communities at least by the earliest Thanetian.UUID:http://zoobank.org/125bd4ab-b172-43d9-80b9-57b75a805150