Ammonoids, commonly known as Ammonites, were sea creatures that belonged to the class Cephalopoda. They possessed an outside shell that was coil-like, with the nautilus of today being its most direct counterpart. Approximately 450 million years ago, the Ammonoidea subclass—often known as Ammonites—first emerged.

Such creatures have been studied since the Jurassic Period, approximately 200 million years ago. The majority of Ammonites disappeared during the end of the Cretaceous Period, 66 million years ago, along with dinosaurs that didn’t possess flight.


Ammonites are known to have existed in a broad assortment of sizes and shapes, ranging from less than an inch to 8 ft wide, according to archaeological records. While some ammonites had helix-shaped shells, others had long, straight shells. However, the majority of species had coil-shaped shells filled with increasingly larger compartments that were divided by tiny walls known as septa.

Interals structures of Ammonite shell
Internal structures of Ammonite shell

As they grew older, Ammonites continuously produced new shell layers, but their bodies were consistently kept in the extraction cell. The walls separating each chamber served as a barrier to prevent the shell from being broken. It had elaborate sutures that bound them to the shell.


Ammonites were thought to be carnivorous creatures. Ammonites possessed spongy tissue with tendrils linked to their heads for capturing prey, just like contemporary cephalopods do today. They had sharp, beak-like mouths to trap prey like plankton, crabs, and other ammonites, according to archeological remains.

Their prey would especially include creatures that are particularly slow swimmers. Some evidence points out Ammonites being scavengers and feeding on already perished creatures left out by bigger predators.


Ammonites were exceedingly prevalent in the Mesozoic epoch. Ammonites frequently lived just over the seafloor that was so low in oxygen levels that they prevented the creation of animal life on the seafloor. This was due to their floating and free-swimming behaviors. When the ammonites perished, they dropped to the seafloor and were eventually covered by accumulated silt.

Ammonite fossil compared to a hand
Ammonite fossil compared to a hand

Even though only a few species of Ammonites frequently persisted, the ammonoids as a whole persisted to exist through multiple significant cataclysmic events. But each time, a small number of species evolved into a variety of forms. As the Mesozoic era came to an end, Ammonite fossils were less common.


Ammonites switched from producing fewer, hefty offspring in the beginning to several smaller hatchlings. They survived three catastrophic extinctions because of their reproductive strategy. The difference in size between some Ammonite shells of the same species is assumed to be due to sexual dimorphism, with the bigger shell, called a macro coach, representing females and the smaller shell, called a micro conch, representing males. 

It is assumed that this is because the female needed a greater body size to produce more eggs. Ammonoids generated a lot of eggs all at once when they neared the completion of their reproductive cycle. It is believed that the eggs floated at the ocean’s surface amid plankton, together with larvae.


Ammonites were preyed upon by numerous marine reptiles such as Mosasaurs, and Ichthyosaurs were natural predators. Similar to contemporary cephalopods, they might have evaded predators by squirting ink, as sometimes, ink is found in fossilized specimens. All in all, Ammonites went exciting 65 million years ago. Whatever the destructive shifts were due to, they would have had an effect on every component of the food chain, especially flora, plankton, and animals that rely on primary nutrition.

Various fossils of Ammonites in a museum
Various fossils of Ammonites in a museum

The loss of Ammonites and non-avian dinosaurs during this period is well known. Mosasaurs, which fed on Ammonites, became extinct as well. The mass extinctions have also been linked to other variables, including climate change and sea level rise.

Facts about the Ammonites

  1. Ammonites managed their buoyancy using a natural pump and siphon system.
  2. The shell’s internal gas chambers were divided by septae. Intricate patterns were produced by the Ammonites’ suture points.
  3. The fossilized remains of Parapuzosia seppenradensis, which can reach about 6 ft across, are the largest Ammonite specimens ever discovered.
  4. Around 65–66 million years ago, Ammonites became extinct.
  5. Originally having a straight shell, ammonites developed a curved shell during the Devonian Period.


Were Ammonite dinosaurs?

Although they existed before and throughout the period of the dinosaurs, ammonites are archaic sea creatures belonging to the group Ammonoidea that are unrelated to dinosaurs. They are technically a type of mollusk.

What is the biggest Ammonite ever found?

Parapuzosia seppenradensis, which lived in the Jurassic Period about 200 million years ago, was the largest Ammonite creature ever discovered. An incomplete specimen discovered in Germany in 1895 had a diameter of 6 ft, and scientists believe the entire shell may well have measured 8-11 ft.

How many Ammonite species were there?

Scientists can distinguish between different types of Ammonites based on a variety of characteristics, such as the structure, age, geography, and characteristics of the shell, such as the frequency and dispersion of ridges, defense spines, or decoration that strengthens the shell. The number of Ammonite species is thought to be around 10,000 and possibly even over 20,000.

Why are Ammonites important to science?

For biologists, ammonites may be a good tool to identify the age of the stones they were fossilized in since they are so widespread and have developed so quickly. Ammonite fossils may also be used to provide information on historical creature climate change responses.

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