The earliest and the southernmost leaf fossils of Dryas from the Upper Miocene Tokachihoroka Formation, eastern central Hokkaido, Japan

Abstract

A new species of mountain avens, Dryas nukabiraensis sp. nov., is described based on well-preserved leaf fossils from the Late Miocene lacustrine mudstone of the Tokachihoroka Formation distributed in Lake Nukabira area, eastern central Hokkaido, Japan. Based on the preservation of the new leaf fossils, which is consistent with predopositional transport, and the mixed physiognomic signals of the co-occurring leaf fossils, as well as the modern climate range of extant Dryas, D. nukabiraensis may have inhabited in an open, boreal to cold-temperate highland environment. The present discovery is important as this species is the earliest fossil record of the genus Dryas, extending its range to the Late Miocene. It also represents the southernmost fossil record of the genus in the Northern Hemisphere. We hypothesize that the genus first appeared at mid-latitude areas of East Asia under boreal to cold-temperate climatic conditions, and subsequently spread to Arctic/Subarctic habitats during the Pliocene and Pleistocene.