The word "ammonoid" is commonly used to refer to a group of extinct marine mollusks that lived during the Mesozoic Era. While ammonoid is the most frequently used term for this type of ancient creature, there are several other synonyms that may be used to describe them. These include ammonite, nautiloid, and cephalopod, which are all terms that may refer to various types of prehistoric mollusks. Other less common synonyms may include belemnite or orthocerid, depending on the specific characteristics of the individual organism being described. Regardless of the term used, however, these ancient creatures remain a fascinating subject of study and discovery for paleontologists and fossil enthusiasts alike.