While you are right that we can't exclude the possibility of animals being consciousness, it's well accepted that their conscious level is very low compared to ours.
Is there some neuroscience backing that? Or is this an argument that consciousness is largely based on having language? Which sounds rather anthropomorphic.
It's an argument by induction. Bacteria (and chair legs) we assume must be less conscious than us. So that sets up a sliding scale with us and the higher mammals at the pinnacle.
What's a conscious level?
That sounds like something a theologian moving the goal posts in light of modern findings would say.
The problem is that the term "consciousness" has too many meanings, and any debate about it seems to devolve into people talking past each other.