The time between dinosaurs and talking monkeys is basically irrelevant. The important figure is the time between the formation of the sun and talking monkeys - 4.5 billion years. You're also making some assumptions about how easy it is to build a ship capable of crossing interstellar distances and also reproducing itself.

In fact, using current technology, we actually could build a "self-replicating probe" loaded with algae and other photosynthetic single-celled organisms. So we really can't rule out ourselves as the evidence we're looking for. We might even be evidence that such probes usually malfunction.