SignificanceSevere coronavirus (CoV) infections have been responsible for hundreds of deaths. Since the emergence of severely pathogenic CoVs, namely the severe acute respiratory syndrome (SARS) virus in 2003, the Middle East respiratory syndrome (MERS) virus in 2012, and the SARS-CoV-2 in 2019, no licensed vaccine or effective antiviral treatment has been developed. Bats are reservoir hosts for many human viruses, including SARS and MERS. The protein relationship between human betacoronaviruses and their bat-specific ancestors is still unknown. This work includes a detailed structure-function analysis of a bat viral macrodomain and provides key insights into features relevant in determining conserved protein functions. This information is vital to the design of macrodomain inhibitors and antiviral therapies.