  We report on the observation of a large anisotropy in the rethermalization
dynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our
system consists of an ultracold sample of strongly magnetic $^{167}$Er
fermions, spin-polarized in the lowest Zeeman sublevel. In this system, elastic
collisions arise purely from universal dipolar scattering. Based on
cross-dimensional rethermalization experiments, we observe a strong anisotropy
of the scattering, which manifests itself in a large angular dependence of the
thermal relaxation dynamics. Our result is in very good agreement with recent
theoretical predictions. Furthermore, we measure the rethermalization rate as a
function of temperature for different angles and find that the suppression of
collisions by Pauli blocking is not influenced by the dipole orientation.
