Do we not know because people haven't gone looking, or because they did go looking and didn't find it? I'm guessing it's the latter, in which case it kinda strengthens the case that there probably isn't some critical role. These are some of the more-studied animals on the planet.

Pointing out risk is a kind of fearmongering when it's technically real but too small to be worth worrying about. Asteroid impact is a real risk too.