Estimated rates of molecular evolution over time, in assessment of possible episodic evolution. Standardized inferred rate of sequence evolution (per data partition) is plotted against inferred age for internal nodes on the optimal mtDNA tree reconstruction (TOptimal) using Multidivtime. Time is given in millions of years before present. No support is shown for an accelerated rate accompanying initial avian diversification or following the K-Pg boundary (vertical dashed line).
Brown et al. BMC Biology 2008 6:6 doi:10.1186/1741-7007-6-6