Dwarf Stegolophodon from the Miocene of Japan: Passengers on sinking boats

A new species of the genus <i>Ocadia</i> (Testudines: Geoemydidae) from the middle Miocene of Tanegashima Island, southwestern Japan and its paleogeographic implications

“…It is interesting that this view is concordant with the recent molecular clock estimation which states that the separation of Ocadia from its close relatives (i.e., an ancestral lineage shared with Ocadia, Chinemys, and M. japonica) occurred in 18-23 Ma ago (the early Miocene; Barth et al 2004). In contrast, the geographic patterns of the early to middle Miocene Ocadia from Japan challenge the paleogeographic hypothesis deduced from the Early to Middle Miocene Stegolophodon (S. pseudolatidens) from Japan (Saegusa 2008). In terms of the latter inference, further discoveries of Miocene Stegolophodon are strongly desired for verification due to the paucity of specimens from southwestern Japan.…”

Anchitherium (Mammalia, Perissodactyla, Equidae) from the early Miocene Hiramaki Formation, Gifu Prefecture, Japan, and its implication for the early diversification of Asian Anchitherium

“…Finally, the nascent Japan became completely archipelagic at least by 16 Ma (Itoigawa, 1993;Ogasawara, 1994;Kano et aI., 2002). According to Saegusa (2008), the dwarfing of Japanese stegodontid proboscideans from the latest Early to early Middle Miocene (ca. 15-17 Ma) has been considered to reflect the archipelagic environment.…”

“…15-17 Ma) has been considered to reflect the archipelagic environment. Around 17 Ma, the mammal dispersal route into proto-Japan via the Korean Peninsula seems to be improbable, but the northern route via Sakhalin (Russia) and/or a route via a chain of islands in the initial Japan Sea are more likely (Saegusa, 2008). Thus, the Chinese Neogene Mammal Faunal Units (NMU, Qiu et aI., 1999), which are a framework to chronologically identify land mammal faunas in East Asia, roughly comparable to the European mammal Neogene zones (MN, Qiu et aI., 1999;Deng, 2006), should be applicable for Early Miocene mammal faunas older than 17 Ma in Japan.…”

“…18.0-18.4 Ma; the Nakamura Formation, ca. 18.4-19.6 Ma) have yielded mammal assemblages including an elephantoid proboscidean Gomphotherium annectens (Matsumoto, 1924;Okumura et aI., 1977;Saegusa, 2008), rhinocerotid perissodactyls Plesiaceratherium sp. and Brachypotherium pugnator (Matsumoto, 1921;Okumura et aI., 1977;Fukuchi, personal commun., 2009), a tapirid perisodactyl Plesiotapirus yagii (Matsumoto, 1921;Qiu et aI., 1991), a plesiosoricid insectivore Plesiosorex sp.…”

“…18.0-18.5,Ma, Lourens et aI., 2004) at the lower part, which also yielded a primitive elephantoid proboscidean, Gomphotherium annectens (Matsumoto, 1924(Matsumoto, , 1926Okumura et aI., 1977). Saegusa (2008) considered that the stratigraphic horizon of Gomphotherium can be roughly correlated to chron C5En, based on stratigraphic correlation to contemporaneous marine sediments in the adjacent Mizunami Basin.…”