Ammonites' shells make the animals look most like nautiluses, but they are actually thought to be more closely related to coleoids. 'Some of their morphology was closer to that of the coleoid group,' ...

Based on the fossil record, ammonites came in a wide range of sizes and shapes, from smaller than an inch to as large as nine feet wide. Some ammonites had long, straight shells, while others had ...

Opalized ammonite fossils are formed through a unique geological process involving the replacement of organic material with silica, which is the primary component of opal. This process can occur ...

Fossils found in the northern part of Hokkaido are a new type of ammonite, the once-ubiquitous spiral-shelled creatures that went extinct with the dinosaurs 65 million years ago, researchers said.