He's been saying that since before The Future is Wild and his Squibbons.

Humans II

I think they could become dominant if they acquired language. Maybe do some crazy sign language with their 8 tentacles. Also their short lifespan could be overcome if they worked together as a group or a hivemind, like the way ants do.

Ants. They already outnumber us. Have larger societies, built in communism.

It's an ant world

It will be dolphin people!