Strigilodus, a stem-ratfish dug out of caves in Kentucky

[Halichoeres]

Like most chondrichthyan fossils, so far we only have teeth, although they're enough to give us an idea of what it was related to. The methods section is one of the more interesting ones I've seen in paleontology, describing how researchers had to crawl into caves, sometimes on their bellies, to pull these teeth out of the cave walls, stowing them individually in cotton-lined vials.

Paper (paywalled, but send me your email and I can get you the pdf): https://www.tandfonline.com/doi/full/10.1080/08912963.2023.2231955

The teeth:

The name means "strigil tooth," after a tool used to scrape oil, sweat, and dirt off of bodies.

And a reconstruction based in large part on its relative Janassa:

[Newt]

Hey, I was in that cave a month ago! Just the easy parts, though, no belly-crawling. I'm going to hit you up for that PDF.

The same formation is exposed near my hometown, and much of it is fossiliferous, but I don't believe it has produced any petalodonts. Vertebrates in general are very scarce in the region.