Estimating the age of the subfamily Orthocoronavirinae using host divergence times as calibration ages at two internal nodes

Viruses of the subfamily Orthocoronavirinae can cause mild to severe disease in people, including COVID-19, MERS and SARS. Their most common natural hosts are bat and bird species, which are mostly split across four virus genera. Molecular clock analyses of orthocoronaviruses suggested the most recent common ancestor of these viruses might have emerged either around 10,000 years ago or, using models accounting for selection, many millions of years. Here, we reassess the evolutionary history of these viruses. We present time-aware phylogenetic analyses of a RNA-dependent RNA polymerase locus from 123 orthocoronaviruses isolated from birds and bats, including those in New Zealand, which were geographically isolated from other bats around 35 million years ago. We used this age, as well as the age of the avian-mammals split, to calibrate the molecular clocks, under the assumption that these ages are applicable to the analyzed viruses. We found that the time to the most recent ancestor common for all orthocoronaviruses is likely 150 or more million years, supporting clock analyses that account for selection.