Here's another one of my "what's its". I thought it was just a fossil of ripples in the sand but something about it looks different. One thing is that there is a spongey layer right under the "ribs". Another thing is that I would expect the tops of the ripples to be worn flat over time but the low areas in between are flat as well. The other thing is that in one photo you can see where one "rib" is broken away from the rock under it. The tiles I took the photo on are 4" across for reference. Oh, and the whole thing is slightly curved like a rib cage. Found in an area of shallow sea creatures : barnacles, sand dollars, some turtle coprolite, etc. There were whale bones found near the same area.