Since sharks are cartilaginous, the only hard part of their body is their teeth. These teeth sink to the ocean floor as sharks grow out of them and remain as fossils that help to understand the history of these animals. Turns out, the oldest fossilised teeth are over 410 million years old!
These teeth belonged to the species Doliodus problematicus. Of course, the oldest sharks don’t look very “shark-like” by today’s standards—while they did have the cartilaginous skeleton and a shark-like jaw and skull, they also had diamond -shaped scales and spines near their fins.
The first group that we might recognise as sharks, the Cladoselache, evolved 380 million years ago. They had the iconic body shape, the dorsal fins, and the forked tail that we attribute to sharks! Then, around 195 million years ago, sharks evolved their strong flexible protruding jaws.