One of the geologists will probably catch this, but my understanding is that radiometric dating, including K-Ar, can't be used on fossil-bearing strata directly, as those are generally sedimentary in origin. Nor, IIRC, can it be used directly on fossils. Radiometric dating is used to date igneous rocks or igneous intrusions that bracket the fossiliferous layers. Other than that, of course, you're right on carbon dating being useless in the context of the OP and subsequent discussion.
Of course, I could be wrong - it's been a REALLY long time since I took a geology course, and new techniques may have replaced my somewhat weak understanding of how all that stuff works.