From the angle and distance shown
Some are vaguely similar to some desert areas I have seen in central and W. Texas, where rock and fossil bits are strewn about. In the photo you have linked to here, some of the pieces look as if they were igneous, with what could be seen as gas bubbles. In the top right quadrant of the photo, there is a piece that at a glance would not be dissimilar to a broken piece of fossil shell material. This is not to conclude in any way that anything in the photo would be fossil at all, just that some vague similarities exist in general shape. I have seen erosion do much stranger stuff. The team at JPL must be excited at this flood of data beyond all belief. What a thrilling time.
Ed