• SPECIES: Perisphinctes sp.
• AGE: 145-166 million years old

These are the pinnacle of evolutionary attempts to defend against predators. This fossil ammonite from the genus Perisphinctes lived during the late Jurassic, between 166 and 145 million years ago. Ammonites are prized for how lovely their many-chambered spiral shells are, but there’s a lot more to them besides their looks.

Seashells like these might not seem that special, but they only exist thanks to the existence of hungry predators, hundreds of millions of years ago. Shells first appeared in the Cambrian Explosion to protect soft-bodied critters from bigger, hungrier predators. And in ammonites, their mineralized body armor is seriously tough. We find ammonite shells with mosasaur toothmarks that didn’t crack through, meaning that these pretty little shells could beat the biggest, baddest marine reptiles of the Cretaceous.