Pliny the elder (the famed Roman philosopher who managed to come up with a wrong theory for everything under the sun) supposed that these strange dark triangles were meteorites that fell from the sky during lunar eclipses. It’s pretty crazy that the truth about these fossils is even cooler than old Pliny’s admittedly rad theory.
Sharks have been a favorite of mine since I was a kid and I’ve just always loved how perfectly adapted they are to their lives in the sea. Their teeth come in all kinds of shapes and sizes, depending on how the shark needs to use them. Some are flattened and serrated to tear flesh, some are thin and needle-like to snatch slippery fish passing by, and some are sharp and broad to slice through just about anything! Evolution swims through our very seas in the form of sharks, and we have so much to learn from them.
Pliny the elder was wrong about the nature of shark teeth but I honestly think his meteorite theory means he hit on the major things you feel upon picking up the fossilized tooth of a shark: this thing is very old, this thing is very cool, this thing is worth being studied and explored. I think we should at least give old Pliny partial credit for that. On the other hand, his theory that rubbing rat poop on one’s head would cure baldness... total swing and a miss.