A new study led by the American Museum of Natural History (AMNH) provides the strongest evidence to date that sharks arose from a group of bony fishes called Acanthodii (‘spiny sharks’).
Analyzing a well-preserved fossil of Doliodus problematicus, a sharklike fish that lived 400-397 million years ago (Devonian period), John Maisey and co-authors identified it as an important transitional species that points to sharks as ancanthodians’ living descendants.
http://www.sci-news.com/paleontology/sharks-acanthodians-04706.html