I think it is just a pebble made of a granitoid rock.
Yes, there is a black component (like with many dino bones), but there are also milky-white grains (as well as the reddish ones). I don't really see a cellular structure, but I do see the basic components of a granite-like rock - potassium feldspar (reddish), quartz (milky white), mafic minerals (can't tell what, dark). The two white blobs inclusions of something softer, perhaps calcite. The dimples are not central or regular enough to be like those of a fossil Ichthyosaur or fish vertebra.