Spelling conventions in the usage of "-alis".

I have recently noticed something about a seeming shift in the way the adjectival suffix -alis was used over time. Earlier (that is, "Classical and earlier") formations such as aeternalis and nervalis displayed a dropping of the nominal/adjectival suffix, -us, from the stem (aetern- and nerv-, respectively) in suffixing with -alis. In later (Post-Classical) formations, however, such as Late Latin actualis and Medieval gradualis, there...

Spelling conventions in the usage of "-alis".