The Meaning of Life, the Universe, and Everything.
Some where you're not.
I saw a screenshot earlier which reminded me of the archeology mechanic that was shown at Minecon Live, and thought that this would be really cool to see added as part of it. The screenshot in question is this one:
During an excavation you'd have a chance at finding the skulls of extinct creatures such as a dragon, or maybe a smaller version of the giant fossils that can already be found, or even just smaller creatures. While these items serve no direct purpose beyond decorative uses I think they'd be a really fun building item, and maybe even serve as inspiration for some builds, or just increase the general appreciation of irl archeology.