Trio of Cretaceous Ammonites — Spiny Form

Alongside trilobites and dinosaurs, ammonites are among the most iconic fossils. Ammonites swam the seas freely during the Jurassic and Cretaceous Periods, evolving rapidly and leaving abundant examples in the fossil record. Ammonites were cephalopods, a taxonomic class that includes today's nautilus, octopus, and squid. They used a long, tubular organ known as a siphuncle to fill or empty their chambers with water and thus move up or down in the water column. Apart from the siphuncle, the animal lived solely in the outermost chamber.

Unlike standard ammonites with tightly coiled shells, heteromorphic ammonites such as Crioceratites nolani developed irregular and surprising shapes, including the prominent spikes that characterize the specimens offered here.