  Exploiting the sensitivity and spatial resolution of the Atacama Large
Millimeter/submillimeter Array (ALMA), we have studied the morphology and the
physical scale of the interstellar medium - both gas and dust - in SGP38326, an
unlensed pair of interacting starbursts at $z= 4.425$. SGP38326 is the most
luminous star bursting system known at $z > 4$ with an IR-derived ${\rm SFR
\sim 4300 \,} M_\odot \, {\rm yr}^{-1}$. SGP38326 also contains a molecular gas
reservoir among the most massive ever found in the early Universe, and it is
the likely progenitor of a massive, red-and-dead elliptical galaxy at $z \sim
3$. Probing scales of $\sim 0.1"$ or $\sim 800 \, {\rm pc}$ we find that the
smooth distribution of the continuum emission from cool dust grains contrasts
with the more irregular morphology of the gas, as traced by the [CII] fine
structure emission. The gas is also extended over larger physical scales than
the dust. The velocity information provided by the resolved [CII] emission
reveals that the dynamics of the two components of SGP38326 are compatible with
disk-like, ordered rotation, but also reveals an ISM which is turbulent and
unstable. Our observations support a scenario where at least a subset of the
most distant extreme starbursts are highly dissipative mergers of gas-rich
galaxies.
