Thanks for the thoughts, Robert.

I think it's highly unlikely, even if there are fossils on Mars, that Opportunity would have stumbled on them so quickly. As many have pointed out, fossils are rare enough on Earth, however I've been in a bed where trilobites are scattered everywhere, and I've seen parts of the Burgess shale where there are a lot of fossils around, so it's not impossible that the rover could have hit it double lucky.

I know what you are saying about interpreting things visually - our brains are hard-wired to see certain patterns plus I intellectually would love to see Martian fossils, so caution is mandatory. Obversely, we have to be careful not to ignore something that slaps us in the face just because it's something we have wished for.

There is a lot to be learned from the images already returned and those yet to come but damn! for a trained paleontologist with a rock hammer, a dental pick and a good lens to be there!

As I said, there are probably good non-biological explanations... but I haven't heard them yet.

On which side of Occam's razor do fossils fall?