The age of the root of placental mammals

The age of the root using MVS and ML branch lengths was estimated after minimizing various penalty functions with the same fossil constraints. All times are in mya, and 95% confidence intervals were estimated by the sum-of-squares method described in Materials and Methods. The times estimated by the r8s program use cross-validation and penalized likelihood methods with essentially the same penalty functions [18], but do not report comprehensive errors.