Ammonitoids: The Primitive Cephalopods of the Mesozoic Era

Ammonitoid is a term used in paleontology to describe a group of extinct cephalopods that are related to modern-day ammonites. Ammonites were a type of shelled marine animals that lived during the Mesozoic Era, which lasted from about 252 million to 66 million years ago. They were characterized by their coiled shells, which were usually spiral in shape and had a distinctive opening at one end.

Ammonitoids are considered to be a subgroup of ammonites, and they are defined as those species that have a more primitive shell structure than other ammonites. This means that they have a simpler shell shape and fewer whorls (spirals) than other ammonites. Ammonitoids first appeared in the fossil record during the Early Jurassic period, around 180 million years ago, and they continued to evolve and diversify throughout the Mesozoic Era.

Some examples of ammonitoid genera include:

* Ancyloceras
* Asperceras
* Ceratites
* Goniatites
* Hemitites
* Inoceramus
* Jeletzkytes
* Kutorginia
* Lituites
* Oxytectum
* Pachytectum
* Parahemitites
* Perisphinctes
* Phylloceras
* Pseudogoniatites
* Sphaeroceras
* Tornoceras

Ammonitoids were an important component of marine ecosystems during the Mesozoic Era, and they played a key role in the food chain as both predators and prey. Many species of ammonitoids are known from fossil deposits around the world, and they are often found in association with other marine animals, such as fish, sharks, and other cephalopods.