Paleogene mammals from the Iwaki Formation in Japan: Their implications for the geologic age and paleobiogeography of this formation. (15th August 2015)

• Record Type: Journal Article
• Authors: Tsubamoto, Takehisa; Koda, Yoshiki; Hasegawa, Yoshikazu; Nabana, Satoshi; Tomida, Yukimitsu
• Is Part Of: Journal of Asian earth sciences. Volume 108(2015)
• Page Start: 18
• Page End: 32
• Publication Date: 2015-08-15
• Subjects: Bothriogenys -- Entelodon -- Notomeryx -- Iwaki Formation -- Eocene -- Japan; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2015.03.049
• Languages: English
• ISSNs: 1367-9120

Abstract

Highlights: Mammalian faunal mixture between northern and southern parts of late Eocene East Asia. Ensure the reliability of Paleogene Asian land mammalian chronology. The Iwaki Formation is correlated to the upper Eocene. Abstract: The mammalian fauna and geologic age of the Iwaki Formation of the Paleogene Shiramizu Group (Iwaki, southern Fukushima, northeastern Japan) are reviewed and previously undescribed specimens are described. The Iwaki mammalian fauna consists of three artiodactyl species: Bothriogenys sp. cf. B. hui (Anthracotheriidae), Entelodon gobiensis (Entelodontidae), and cf. Notomeryx sp. (Ruminantia). These three genera indicate an Ergilian Asian Land Mamma Age (=late Eocene [Priabonian] equivalent) correlation for the Iwaki Formation, demonstrating that the Eocene–Oligocene boundary exists within the Shiramizu Group. These three genera have never co-occurred in a single formation, although in Asia they have been recorded only in the late Eocene. In Asia, Bothriogenys has been recorded in the southern and middle regions, Entelodon has been mostly recorded in the northern and middle regions with one exception from the southern region, and Notomeryx has been recorded in the southern region. The co-occurrence of these three genera in the Iwaki Formation implies that Bothriogenys, Entelodon, and perhaps also Notomeryx can be useful late Eocene indicators in terrestrial eastern Asia. It also suggests that the Iwaki mammalian fauna is paleobiogeographically located between the northern and southern late Eocene faunas of eastern Asia, showing some faunal mixture. The Iwaki fauna is also unique in comprising diverse faunas of marine sharks and seashore birds together with terrestrial mammals. The Iwaki vertebrate fauna is key for reconstructing the faunas of the eastern coastal margin of the Asian Continent during the late Eocene.