Reason alone cannot create evidence. Reason only considers alternative possibilities from the available evidence and notes consistency. Therefore, reason is completely limited to the quantity and quality of experience. Reason also doesn't test whatever possibilities it derives, so it has no means of providing proof with which to substantiate evidence. Methodology and measurement are used to both increase the quantity and quality of experience and to experiment therefore providing proof with which to substantiate evidence. Your view is flawed because you believe with limited knowledge, you could perfectly reason out the entire world.
Take for example the belief of spontaneous life. People used to observe maggots crawling from meat and frogs crawling out from the mud and so they reasoned that flies were created from rotting meat and frogs were created from mud. They had a piece of knowledge based on observation, "Flies found on meat, and frogs found in mud" but they incorrectly reasoned. Only via experimentation was this belief that had lasted for centuries able to be overturned, because the reasoning seemed so infallible. In fact all of our progress has been through science and the subsequent reasoning and testing of our experiences.
Reason is only the tool of experience, and it cannot exist separate from it. Even in your own example. How would someone know that a dinosaur could eat another dinosaur unless they had observed animals eating other animals before? Reason is learned from our experience and it is limited by it.