If you ever encounter a horseshoe crab on the beach, you are a looking at a creature that would not have appeared out of place hundreds of millions of years ago.
This is a clear falsification of an evolutionary expectation expressed across many years, and widely held by a consensus of experts.
The whole point of “fitness,” in an evolutionary context, is reproduction. One has higher “fitness” if one can have more offspring.
According to evolution, the species arose as a consequence of random events, such as mutations.