Sharks are paleontological paradoxes. They have an extensive fossil record going back 409 million years, yet, except in cases of exceptional preservation, little more than their teeth remain. They are everywhere yet are nearly invisible, their identity and appearance often contingent upon what we know about their living relatives.

But what do you do when you’ve got a shark tooth that doesn’t resemble the dentition of any species known to swim the modern seas? That’s the puzzle the late paleontologist Shelton Applegate faced while studying the different fossil shark teeth of Pyramid Hill. Among the teeth found at this 23 million year old site in the San Joaquin Valley were small, hooked teeth with little nubs of