The first generation games were pretty much a scaffold holding the combat system to Character generation and/or advancement. Most were pretty close to Minis games with permission to go beyond the rules. D&D, V&V, EPT, Metamorphosis Alpha, Gamma World.
While CT may be 1977, it and RuneQuest (1978) are pretty much the early versions of the second generation: the character has backstory and advancement along a pseudo-Campbellian monomyth is usually absent. Skills take over in their generation - which lasts to about 1983, really...
A third wave of approach was the skills by class & Level approach of a number of 1979-1985 introductions: Palladium's Mechanoids and Palladium FRPG; Bard Games' The Arcanum; ICE's Rollmaster, Spacemaster, MERP, and the later Cyberspace (1989); and the later Justifiers (StarChilde 1988). These games also tend to either have a unified resolution system, or two - combat vs non-combat.
A fourth wave, which starts early, but really doesn't hit stride until later, are the point-builders: TFT, Champions, GURPS, several smaller superhero games, Mechwarrior 1E. Again, most of these have either one or two resolution systems, used consistently.
The 5th wave tends to be the dice pool games of the late 1980's onward. WEG Star Wars; WWG's VTM, WWTA, MTA, WTO, CTD; FASA's Shadowrun. Mostly, these continue the unified resolution mechanic.
An alternate identity for 5th wave is priorities based character design. Mechwarrior 2E, all the WWG games, Shadowrun...
the 6th wave is mid-90's... the rise of the Story-Game. Many RPGers don't encounter them until the early 00's... mechanics become less about simulating a (sur)reality and more about guiding the story. These rise out of reactions to (most especially)
The 7th wave is d20... Further despondence sayeth not.
The 8th wave is the Retroclones (S&W) and Pseudoclones (C&C) - games aiming for the feel of the first gen, but with smoothed mechanics.
After that, the model breaks, because all the prior waves continue to have market presence. Rifts is still skills by class and level. HARP is a lighter version of Rolemaster... but RMSS is still available for the hardcore.
Some games are hard to fit...
RTG's Cyberpunk is class providing one unique skill, lifepath providing background, and points spent for everything else; other interlock games vary from starting skill package to just spend the points...
FASA Trek is a skills and background, but is a cadet of RuneQuest... essentially, a bunch of Traveller Grogs used a traveller like lifepath with a Chaosium style skill system, and Snapshot-like combat system...
The first skill driven (rather than class & level driven) game really seems to be Traveller. Chaosium's RuneQuest is second.
Hero System is the best known point-builder of the early 1980s... but it wasn't the only one.
TFT can be seen as a point builder - atts are race base plus X points, and talents are by filling "slots" equal to IQ; more talents needed? Get more IQ. The new edition is changing that...
Twilight 2000 1E is skill driven, feels earlier than it's mid 80's writing date, and is a unified skill mechanic. It feels very much like what FASA did with Star Trek... Traveller CG mode, and RQ skills and action resolution mode.
T2K 2E goes to lifepath earns points to spend on skills.
Later Traveller: MT is pretty much CT+Task System; unification of the mechanic, but still being predominantly a 2nd wave game. T2300, however, is a hybrid lifepath and point builder. TNE is T2K 3e... in the remnants of the OTU. T4 is, like MT, CT with a task system, but with a change in how many skills, and a bunch of "You may pick instead" options on the tables.
T20 is the D20 system flavor.
GT is the GURPS system flavor.
HT is the Hero System flavor.
MGT is a pseudoclone. It wasn't trying to be the original, but to be compatible enough, yet while having a unified mechanic.
The Big Caveat:
Any such cladistic analysis ultimately fails to capture the whole of the gaming ecosystem.