| Method |
The extinct genus Karnimata (11.1 - 6.4 Ma) is interpreted as a member of the lineage leading to Rattus. The oldest record (11.1 Ma) is uncertain, but the next (at 10.4 Ma) is unquestionable. The early species, Progonomys hussaini (11.5 - 11.1 Ma) is interpreted as an undifferentiated basal murine antedating the common ancestor of Mus and Rattus by Jacobs and Flynn (2005), and so they place the Progonomys-Karnimata split (equivalent to the Mus-Rattus split) at not much beyond 11 Ma, ‘although it may be younger’. The dating is based on detailed field stratigraphic study of the long Siwaliks sedimentary sequence, with dating from magnestostratigraphy and radiometric dating (Johnson et al. 1985 Barry et al. 2002). The soft maximum constraint on this date is taken as the oldest record of Progonomys at 12.3 Ma. |