Advanced intelligence may be built into life itself. The idea is already out there to send an army of self-replicating biotech to scour other planets. What would be easier to send on interstellar missions, an elephant, or a cockroach? The latter obviously.

How bout this: The dinosaurs reached a state more advanced than ourselves, but realized that they could not go any further. They decided to retire to a lower-energy form, with smaller brains, and a more diverse ecology. They integrated themselves with the environment, and in the lowest energy state aimed to outlive every other form of life on Earth.