Some sharks have teeth that are flat and very strong. They are typically found in species that live at the bottom of the ocean and feed on hard-shelled animals such as crabs and shelled molluscs.

Turns out, the palm-sized tooth belonged to an animal that died at least 3.5 million years ago: an Otodus megalodon shark. "She told me she was wading in knee-deep water when she saw it and dove ...