Ammonite, Iridescent (Placenticeras)

Cretaceous. Bear Paw Formation. Southern Alberta, Canada. From the Devonian Period to the end of the Cretaceous, ammonites generated tens of thousands of species that invaded nearly every salt-water habitat in the world. Ammonites species came so fast and furiously that the average species only lasted a million years or less. This quick turnover means that ammonites are near-perfect paleo-clocks.