From the University of Vienna:
Cartilaginous fish have changed much more in the course of their evolutionary history than previously believed. Evidence for this thesis has been provided by new fossils of a ray-like shark, Protospinax annectans, which demonstrate that sharks were already highly evolved in the Late Jurassic. This is the result of a recent study by an international research group led by palaeobiologist Patrick L. Jambura from the Department of Palaeontology at the University of Vienna, which was recently published in the journal Diversity.
Cartilaginous fishes (sharks, rays, and ratfish) are an evolutionarily very old group of animals that already lived on earth before the dinosaurs more than 400 million years ago and have survived all five mass extinctions. Their fossil remains can be found in large numbers all over the world – however, usually only the teeth remain, while the cartilaginous skeleton decays together with the rest of the body and does not fossilize. (February 28, 2023)
Do we ever find the truly primitive shark?
The paper is open access.