to become part of the field population. For a majority of clusters in the galaxy, the latter is the common outcome . However, recent discussions consider that cluster morphology is more heterogeneous [@Bressert:2010fk; @de-Grijs:2011rt]. Numerical studies suggest that small groups of stars may be abundant [@Adams:2001aa] and they may either merge to form clusters or disrupt rapidly into the field. According to studies like that of @Kruijssen:2012ve, star clusters may assemble from sub-clusters that merge into larger entities after the gas from which they formed is both disrupted by stellar feedback and torn apart by tidal shocks from the surrounding cloud (the so called “cruel cradle" effect).

Unfortunately, the dynamical picture of cluster evolution provided by numerical studies is difficult to directly compare with observations. On one hand, the initial conditions of cluster formation, a key requirement for realistic simulations, are still under debate. On the other hand, young cluster evolution from observations, would require of additional information on the kinematics of stars (e.g. radial velocities), and spectroscopic age estimations of individual sources to infer the progression of formation. Such studies are only beginning to arise from surveys like APOGEE[^1] [e.g. @cottaar:2014aa], and are limited to nearby ($d<1$ kpc) regions. 