English: This figure shows the profile of the cost function with respect to the age of the root estimated by three different cost functions. Because the root age estimated by function FADD was going to infinity, it was set to 200 mya for illustrative purposes. Figure A is a single example from a tree simulated under the scenario of random auto-correlated changes of rate moving towards the tips, strongly biased towards a deceleration of evolutionary rates as time progresses (from the set of simulations used for Table 3). The true age of the root was 100 mya. Figure B shows the results using the MVS tree derived from the mitochondrial sequences of placental mammals. The dotted line indicates the 95% confidence interval of the estimated age of the root using the sum-of-squares approach described in Materials and Methods.