Aside from the obvious source of the ribs, there are differences in size, ratios of fat to meat, and cooking times. Pork ribs are reasonably lean, at least when compared to beef ribs. The upper portions of the pig's ribs are meatier, and the fat content increases as you go lower. With beef ribs, you'll see more even portions of meat vs. fat throughout the slab. Beef will be fattier than pork, but you'll also get more meat per bone. Size-wise, beef ribs can be 8-12 inches long, whereas pork ribs are usually 3-6 inches long. And the larger the slab, the longer they'll need to cook.