[Flyndaran]

One problem is that not only that technological species would have to be unknown. All of its other high intelligence relatives would as well. For humans, all other primates would have to be missing from the fossil record.
There really aren't any non-mammalian animals on par with primates other than cephalopods. And I don't think it's possible for purely aquatic creatures to progress past middle stone age.
Of course stone age soft bodied invertebrates could have evolved and disappeared from the oceans many times without leaving anything we would identify as proof.