Correlation chart relating Subathu Formation stratigraphy to the Eocene time scale and showing evidence constraining the geological age of H. subathuensis. Time scale, planktonic zonations (P and NP), and radiometric calibration are from Berggren et al. (10) as correlated with sea-level sequence stratigraphy by Hardenbol et al. (11). Shallow-benthic foraminiferal zonation (SB) is from Serra-Kiel et al. (12). Note low sea stands and the positions of major unconformities (U) just before and after the Ypresian–Lutetian early-to-middle Eocene boundary. The Kuldana-Kalakot faunal zone that yields Pakicetus in Kashmir and Pakistan (box with arrow) overlies beds with Assilina exponens and Assilina spira of shallow benthic zones SB13–14 here (9, 12) and beds with Orbitolites complanatus of shallow benthic zone SB12 elsewhere (12, 13), indicating that they are early middle Eocene in age. The Subathu zone IIIc marine fauna with H. subathuensis (box with arrow) is associated with Nummulites atacicus of shallow benthic zone SB8 (9, 12), indicating that Himalayacetus is middle early Eocene in age.