Acanthodians, or "spiny sharks," were in the news recently when new evidence linking them to the earliest sharks (not a new idea) was encountered.

"Doliodus provides the strongest anatomical evidence to date that chondrichthyans arose from "acanthodian" fishes by exhibiting an anatomical mosaic of "acanthodian" and sharklike features."

Maisey et al. (2017): http://digitallibrary.amnh.org/handle/2246/6701