Yes and no. They have been a distinct groups for that long, in fact longer, out to some 400 million years. And most all would have been outwardly recognizable as "sharks" to the average observer. Yet "unchanged" seems a totally inappropriate word to apply to sharks. Within the broad paradigm of "sharkiness" they've proven highly adaptable and variable.
In modern sharks you have everything from the "normal" mid water predators (some of which must remain constantly moving to "breathe"), to lugubrious bottom feeders like the nurse shark, to huge behemoths like the "whale shark" that filter feed on plankton at the surface like baleen whales. There's similar diversity, with the occasional "odd ball," among ancient sharks. (IIRC there are well over 2,000 species of fossil sharks. Compare to well under 1,000 species among all dinosaurs.)
Yeah, as a certifed PADI Advanced Open Water Diver, I'm familiar with the diversity of sharks. But deciding to be a dolphin pod and growing neon bioluminescent billbords? No way. I laughed my butt off.