Where: Hokkaido, Japan (43.3° N, 143.8° E: paleocoordinates 44.6° N, 141.4° E)

• coordinate estimated from map

When: Upper tuffaceous silstone Member (Morawan Formation), Chattian (28.1 - 23.0 Ma)

• Biostratigraphy indicates a mid-Rupelian age for the lowermost (Lower Hard Shale) member of the Morawan Formation [33, 34], as well as an earliest Chattian age for the bottom of the overlying Kiroro Formation [35, 36]. Together, these estimates constrain the age of A. polydentatus to the latest Rupelian or earliest Chattian. However, this is difficult to reconcile with markedly younger radiometric estimates, which suggest an age of 23.3 ± 0.7 Ma for the bottom of the Kiroro Formation, 28.6 ± 0.7 Ma for the Honbetsuzawa Formation underlying the Morawan Formation, and 26.1 ± 0.7 Ma for the upper part of the Middle Hard Shale Member of the Morawan Formation, which underlies the UTS [37, 38]. Until further data are available to resolve this issue, the age of A. polydentatus is therefore here assumed to be 26.1–23.3 Ma (early–late Chattian). (Marx & Fordyce, 2015)

• member-level stratigraphic resolution

Environment/lithology: basinal (siliceous); siltstone

Size class: macrofossils

Preservation: original phosphate

Collection methods: surface (float),

Primary reference: L. G. Barnes, M. Kimura, H. Furusawa and H. Sawamura. 1995. Classification and distribution of Oligocene Aetiocetidae (Mammalia; Cetacea; Mysticeti) from western North America and Japan. The Island Arc 3(4):392-431 [M. Uhen/M. Uhen/M. Uhen]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 45786: authorized by Mark Uhen, entered by Mark Uhen on 01.12.2004

Creative Commons license: CC BY (attribution)