Ammonite Fossil

Ammonites appeared in the fossil record approximately 240 million years ago during the Triassic period and disappeared around 65 million years ago at the end of the Cretaceous. They were predatory mollusks related to the Nautilus and modern-day Squids. This specimen is Hoploscaphites nicolletii, found in the Fox Hills Formation of South Dakota. It lived during the Upper Maastrichtian, Late Cretaceous era, around the time of the K-Pg extinction event that caused the extinction of all non-avian dinosaurs.

Covered in a Mother of Pearl nacreous shell, the Ammonite’s iridescence is due to the Aragonite found in the shell. As light travels and bounces through the layers of Aragonite, a rainbow spectrum can be observed. Thicker layers of Aragonite can lead to deep shades of red and orange, while thin layers can display shimmering greens and dainty violets.