Chikubetsu (Miocene of Japan)

Where: Hokkaido, Japan (44.4° N, 141.9° E: paleocoordinates 45.3° N, 139.8° E)

• coordinate stated in text

When: Sankebetsu Formation, Aquitanian (23.0 - 20.4 Ma)

• The age of the Sankebetsu Formation was estimated based on fission-track (FT) dating, marine molluscs, and diatom fossils (Kurita et al., 1992; Noda, 1992; Kafanov et al., 2005). FT ages for the upper part and base of the formation were reported as 20.6±1.0 Ma and 23.8±1.5 Ma, respectively (Kurita et al., 1992). The molluscan fauna (e.g. Mytilus tichanovitchi, Macoma osakaensis, Megayoldia (Hataiyoldia) tokunagai, and Neilonella (Borissia) sakhalinensis) indicates that the formation was deposited in the early Miocene (Kafanov et al., 2005). The diatoms indicate ages from 24.0 Ma to 20.3 Ma (Thalassiosira praefraga zone; Hata et al., 1988; Kurita et al., 1992), consistent with the FT ages. The locality of the present specimen is more upstream than the sampling point for the FT analysis. The float’s age is likely older than the FT ages, as the ages of strata become older upstream in this area. In conclusion, the possible age of the present specimen can be constrained between 25.3 Ma (oldest estimate based on FT, including the possible error of 20.6±1.0) and 20.3 Ma (youngest estimate based on diatoms).

• formation-level stratigraphic resolution

Environment/lithology: marine; gray sandstone

• The Sankebetsu Formation consists of massive, tuffaceous, fine- to medium- grained gray sandstone.

Size class: macrofossils

Primary reference: K. Matsui and S. Kawabe. 2015. The Oldest Record of Paleoparadoxia from the Northwest Pacific with an Implication on the Early Evolution of Paleoparadoxiinae (Mammalia: Desmostylia). Paleontological Research 19(3):251-265 [M. Uhen/M. Uhen]more details

Purpose of describing collection: general faunal/floral analysis

PaleoDB collection 171611: authorized by Mark Uhen, entered by Mark Uhen on 14.07.2015

Creative Commons license: CC BY (attribution)

Taxonomic list

 Perissodactyla - Paleoparadoxiidae
Paleoparadoxia sp. Reinhart 1959 desmostylian