  We report on the observation of heteronuclear magnetic Feshbach resonances in
several isotope mixtures of the highly magnetic elements erbium and dysprosium.
Among many narrow features, we identify two resonances with a width greater
than one Gauss. We characterize one of these resonances, in a mixture of
$^{168}$Er and $^{164}$Dy, in terms of loss rates and elastic cross section,
and observe a temperature dependence of the on-resonance loss rate suggestive
of a universal scaling associated with broad resonances. Our observations hold
promise for the use of such a resonance for tuning the interspecies scattering
properties in a dipolar mixture. We further compare the prevalence of narrow
resonances in an $^{168}$Er-$^{164}$Dy mixture to the single-species case, and
observe an increased density of resonances in the mixture.
