SignificanceA single family of cressdnaviruses is known to infect vertebrates, theCircoviridae. Here, we identified a second that has historically infected saurians, naming them theDraupnirviridae. The initial clue was that some draupnirviruses donated theirRepgene to poxviruses exclusively infecting birds and their relatives. Since this implied the donors also infected vertebrates, a search for draupnirvirus-derived endogenous viral elements was done in ~25,000 eukaryotic genome assemblies. This confirmed that some draupnirviruses infected saurian vertebrates as long ago as the Cretaceous Period, over 100 million years before present, and they still circulate today. We propose that their evolutionary path likely began with protist-infecting ancestors, followed by emergence in insects, and eventual transfer to vertebrates by blood feeders.