  We report numerically exact quantum scattering calculations on magnetic
Feshbach resonances in ultracold, strongly anisotropic atom-molecule [Rb($^2$S)
+ SrF($^2\Sigma^+$)] collisions based on state-of-the-art ab initio potential
energy surfaces. We find broad resonances mediated by the intermolecular
spin-exchange interaction, as well as narrow resonances due to the
intramolecular spin-rotation interaction, which are unique to atom-molecule
collisions. Remarkably, the density of resonances in atom-molecule collisions
is not much higher than that in atomic collisions despite the presence of a
dense manifold of molecular rotational states, which can be rationalized by
analyzing the adiabatic states of the collision complex.
