Make a very rare (cherry grove or mangrove swamp rarity) subbiome in the desert called the "fossilized wastes", which not only have fossils underneath the ground, but also have large ribs similar to the soul valley bones sticking out. Sandstorms are frequent here, which cloud your vision, allow skeletons to spawn, and also signify that this is a primal, dangerous part of the desert. Villages don't spawn here. Near the big ribs and skulls and tusks and whatever other bones they add as remnants of the ancient overworld, there are high concentrations of sussy sand which contain bones. Most of these are normal, but some special "fossil fragments" could be reassembled into a sniffer skeleton or a skeleton of another ancient mob, which you could then put on display.