We present GTC/OSIRIS optical spectra of 4 of the most compact and massive early-type galaxies at redshift $z\sim1$, with effective radii $\Reff=0.5 - 2.4$ kpc and photometric stellar masses $\Mstar=1.2 - 4\times10^{11} \Msun$. We find these galaxies have velocity dispersions $\sigma = 156 - 236$ \kms. We find that: i) the dynamical masses of these galaxies are systematically smaller by a factor of $\sim$6 than the previously published stellar masses; ii) when estimating stellar masses as 0.7$\times$\Mdyn, a combination of passive luminosity fading with mass/size growth due to minor mergers can plausibly evolve our objects to match the properties of the local population of early-type galaxies.