The first were raised before the SYW, and more were raised durin it (the 'captured' saxon battalions were formed into Prussian Fusilier Bns, not Musketeers).
These Regts were 2nd line troops (seniority below musketeer regts), and were cheaper to raise/maintain (and generaly accepted as lower training and elan than the bulk of musketeer regts).
I'd need to look at what became of these regiments by 1787 in terms of lineage, but there were certainly 'fusilier' regts well before 1787.
Daryl