Forgive me please in advance, because my copy of Goldsworthy disappeared during a recent move, as things tend to do.
Who led cohorts during post-Marian reforms (and pre late/late empire developments)? This is not mentioned in the cohort or Roman military org articles on Wikipedia and I don’t recall an answer in Goldsworth. Similarly, who led maniples pre-Marian reforms? For the later question, I assume a junior equestrian, and for the former I’m assuming a junior equestrian or an experienced centurion. But I real have no idea. OR was there no direct commander of cohorts, aside from the legatus legionis (legionary commander?)
Second question, within a cohort would centuries be directed for individual action, in the way companies have been? Or would the battalion equivalent (the cohort) effectively operate solely as single unit, with any individual century movement being undertaken in a centurion’s initiative or direct order from legionary command, thus negating the need for a cohort commander?
Thank you in advance? Also, any sources/book recommendations would be appreciated!
We don't know for sure who led individual cohorts in any given post-Marian army. I agree with Cagniart that it was most likely the senior centurion (of the six contained within the cohort). He in turn reported to whoever was directly above him with imperium (a legatus like Labienus under Caesar, for instance).
As usual, the best evidence for how armies moved around on the battlefield at the sub-legion level is Caesar, and he basically never talks about the manoeuvers of individual centuries. He barely mentions centuries at all, though he mentions centurions quite a lot. He talks about the movements of cohorts fairly often, though. For instance, in BG Book V, as the ill-fated force of the legates Sabinus and Cotta are surrounded outside the castra, Caesar tells us that individual cohorts would make attacks in attempt to break free: cum quaepiam cohors ex orbe excesserat atque impetum fecerat, hostes velocissime refugiebant ("when any cohort had moved out of the circle and made an attack, the enemy very quickly danced withdrew" 5.35). Likewise, later in that same paragraph, we see the dutiful Cotta "encouraging all the cohorts and the ranks" (omnes cohortes ordinesque adhortans). This of course isn't definitive, but it does suggest that Caesar conceptualized actions on the cohort-level, not the century level.
Having said that: there is no reason why individual centuries could not act individually under their centurion, though of course their basic mandate was to work with their five fellow centuries to present a unified force. This is the whole point of the cohort switch, after all: a larger, more cohesive force than the many maniples, better suited to face the larger enemy fronts of the 2nd and 1st centuries (like the German hordes faced by Marius).