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. Scientists estimate that there were at least 10,000 species of ammonite during their roughly 150-million-year reign on Earth, and pos🎀sibly up to 20,000 species.

The oute🤡rmost layer of ammonite shells was made up of aragonite, a type of calcium carbonate, which provided strong protection and allowed ammonites to fossilize much more readily than animals that either had a soft shell or lacked a shell. Because ammonites rapidly evolved into new species and their shells were prone to fossilization, they have been crucial for scientists interested in dating the Earth's layers: finding th♒e same species of ammonite in layers of soil thousands of miles apart implies that those layers are from the same time period in Earth's history.

Ammonites are cephalopods, a class of mollusk that includes present-day nautilus, octopus, and squid. Cleoniceras lived during the Albian Stage of the Early Cretaceous Peri🍸od, roughly 110 million years ago. This fossil shows gorgeous and intricate suture lines where the walls separating each chamber, known as septa, joined the wall of the shell. Although scientists once believed that the intricate suture lines strengthened the shell and supported the animals in deep waters, it is now believed that the suture lines helped with buoyancy regulation and made it harder for predators to puncture their shells. Ammonite suture lines are unique to each species, and thus the patterns on different ammonites help with species identification.