Because 450 million years ago was so long ago, there is virtually no definite way of recreating what creatures from that time period looked like, but using skeletons and fossils, it is possible to make guesses.
Sharks are a type of creature that exist today that are known to have existed even 200 million years before dinosaurs walked the Earth, and yes they still exist today, however they wouldn't have looked like they do now.
Fossil discoveries suggest that sharks had many different forms throughout evolution. Some started with eel-like bodies, and others had strange heads. On the other hand, sharks always needed flexible bodies and replaceable teeth because these are just the things that make a shark a shark.
As oceans became acidic, it's believed that only 1% of marine species were able to survive, probably by going into deeper waters. Among those marine species were some shark species, and those have evolved into what we have today.