Not if it were indigenous to the Earth. There has never been any fossil discovered of creatures large enough to have interesting brains. Of course brains do not fossilize very well! But the point is that you would have to hypothesize creatures mostly gelatinous like the octopus living at a time when the fossil record shows no animals larger than amoeba! Nature has never been observed to create two-tiered systems like this with out intermediate- sized creatures to fill the in-between niches. We can speculate, but in the end we have to be led by the fossil evidence first.