A family of amateur fossil hunters from Utah -- the Gunthers -- found this fascinating fossil in the Spence Gulch shale part of Utah in 1992, and shared it with Richard Robison at the University of Kansas. The mystery of what it was went unsolved for nearly 30 years, until a team at Ohio State uncovered the telltale circle that showed the creature had attached to a shelly surface via a basal disc. It's the earliest/one of the earliest known specimens of a mat-sticker making the evolutionary move to attaching to a harder surface--a leap that makes some of our modern-day echinoderms, including sea cucumbers, possible. They recently published their findings in the Bulletin of Geosciences but this discovery wouldn't have been possible if the Gunthers hadn't found the fossil in the first place. Just fascinating stuff.
(story here: https://news.osu.edu/scientists-discover-evolutionary-link-to-modern-day-sea-echinoderms/),