  Interpreting the scaling relations measured by recent large kinematic surveys
of $z < 1$ galaxies has remained hampered by large observational scatter. We
show that the observed ISM and morpho-dynamical properties along the average $z
\sim 0.6$ major merger describe a very self-consistent picture in which star
formation is enhanced during first passage and fusion as a result of
gravitational perturbations due to the interaction, while the gas velocity
dispersion is simultaneously enhanced through shocks that convert kinematic
energy associated with bulk orbital motions into turbulence at small scales.
Angular momentum and rotation support in the disc are partly lost during the
most perturbing phases, resulting in a morphologically compact phase. The
fractions of present-day E/S0 versus later type galaxies can be predicted
within only a few per cent, confirming that roughly half of local discs were
reformed in the past 8-9 Gyr after gas-rich major mergers. Major mergers are
shown to strongly scatter scaling relations involving kinematic quantities
(e.g. the Tully-Fisher or Fall relations). Selecting high-z discs relying only
on $V/{\sigma}$ turns out to be less efficient than selecting discs from
multiple criteria based on their morpho-kinematic properties, which can reduce
the scatter of high-z scaling relations down to the values measured in local
galaxy samples.
