I'm pretty sure a fish fossil that close to the surface wouldn't survive billions of years of erosion from the atmosphere.

Realistically using Earth as an example there wasn't even close to enough time where Mars was habitable for complex multicellular life to evolve, only microbes.

Just for reference the first single celled life evolved on Earth 3.7 billion years ago, but the first complex multicellular life first evolved 600 million years ago.