That's entirely possible. But if we look at natural history, we see a continuum, don't we?
Kind of, but not really. Fossilization is extremely rare, particularly with soft bodied and single celled creatures, so there isn't really a continuum. More like patches of information from all over the temporal map.
If reasoning skills are shown to exist on a continuum, is it reasonable to suppose that we are the apex, or that something greater isn't possible?
It's reasonable to suppose that we are the apex right now for lack of evidence for anything better.