  We present the first study of spatially integrated higher-order stellar
kinematics over cosmic time. We use deep rest-frame optical spectroscopy of
quiescent galaxies at redshifts z=0.05, 0.3 and 0.8 from the SAMI, MAGPI and
LEGA-C surveys to measure the excess kurtosis $h_4$ of the stellar velocity
distribution, the latter parametrised as a Gauss-Hermite series. Conservatively
using a redshift-independent cut in stellar mass ($M_\star = 10^{11}\,{\rm
M}_\odot$), and matching the stellar-mass distributions of our samples, we find
7 $\sigma$ evidence of $h_4$ increasing with cosmic time, from a median value
of 0.019$\pm$0.002 at z=0.8 to 0.059$\pm$0.004 at z=0.06. Alternatively, we use
a physically motivated sample selection, based on the mass distribution of the
progenitors of local quiescent galaxies as inferred from numerical simulations;
in this case, we find 10 $\sigma$ evidence. This evolution suggests that, over
the last 7 Gyr, there has been a gradual decrease in the rotation-to-dispersion
ratio and an increase in the radial anisotropy of the stellar velocity
distribution, qualitatively consistent with accretion of gas-poor satellites.
These findings demonstrate that massive galaxies continue to accrete mass and
increase their dispersion support after becoming quiescent.
