Difference Between Ammonite and Nautilus

The key difference between ammonite and nautilus is that ammonite is a marine mollusc of subclass Ammonoidea, which is extinct, while nautilus is a marine mollusc of subclass Nautiloidea, which is extant species.

Class Cephalopoda includes exclusively marine animals with bilateral symmetry. These molluscs are highly advanced and organized. Cephalopods are the largest of all molluscs. Ammonoidea and Nautiloidea are two subclasses of class Cephalopoda. Ammonoidea includes extinct ammonites, while Nautiloidea includes extant species. Ammonite and nautilus are two similar types of marine molluscs. They have spiral chambered shells. Ammonites are predecessors of Nautilus. Ammonites appeared in the Devonian period, while nautilus appeared in the Late Cambrian.

CONTENTS

1. Overview and Key Difference
2. What is Ammonite 
3. What is Nautilus
4. Similarities Between Ammonite and Nautilus
5. Side by Side Comparison – Ammonite vs Nautilus in Tabular Form
6. Summary

What is an Ammonite?

Ammonite is a member of subclass Ammonoidea. It is an extinct marine mollusc. Ammonites appeared in the Devonian period. Ammonites and nautilus look similar. They had a spiral, chambered shell. They could retract their bodies inside the shell for protection.

In ammonites, the siphuncle ran along the outer edge of the shell. This shell had 26 chambers. They had complex septa that were convoluted or wrinkled. The colour of shells was unknown since they are found as fossils. The reason behind the extinction of ammonites is still in debate. Major reasons might be their restricted distribution, large amounts of acid rain falling into the sea and the shedding of light.

What is a Nautilus?

Nautilus is a member of the subclass nautiloidea of Cephalopoda. It is a marine mosllusc similar to ammonite. Subclass Nautiloidea includes extant species of molluscs, especially two genera of six nautilus species. Similar to ammonites, nautilus species have a coiled chambered shell. However, their shell is smooth and has 30 chambers. The septa are simple and smoothly curved.

Moreover, unlike in ammonites, the siphuncle of the nautiloids runs through the center of the shell. Nautilus appeared in the Late Cambrian. Extinct ammonites are relatives of nautiloids.

What are the Similarities Between Ammonite and Nautilus?

• They are similar organisms belonging to the kingdom Animalia, phylum Mollusca and class Cephalopoda.
• Ammonite and nautilus are marine molluscs.
• They are pelagic animals.
• Ammonites were the predecessors of living nautiluses.
• They have coiled chambered shells.
• Both are believed to be scavengers feeding on a variety of dead animal matter.

What is the Difference Between Ammonite and Nautilus?

Ammonite is a member of subclass Ammonoidea of class Cephalopoda, which is an extinct marine mollusc. On the other hand, nautilus is a member of subclass Nautiloidea of class Cephalopoda, which is an extant marine mollusc. So, this is the key difference between ammonite and nautilus. Besides, ammonites appeared in the Devonian period while nautilus appeared in the Late Cambrian.

Moreover, another major difference between ammonite and nautilus is that the siphuncle ran along the outer edge of the shell in ammonites while the siphuncle runs straight through the center of the shell in nautilus. Also, septa are complex in ammonites while septa are simple in nautilus.

The below infographic lists the differences between ammonite and nautilus in tabular form for side by side comparison.

Summary – Ammonite vs Nautilus

Ammonite and nautilus are two-chambered shelled molluscs. They are marine animals that are invertebrates. They belong to the class of Cephalopoda of kingdom Animalia. Ammonite and nautilus are closely related to marine molluscs. Ammonite is an extinct mollusc, while nautilus is an extant mollusc. The siphuncle ran around its shell’s outer edge through the edge of every septum in ammonites. In contrast, the siphuncle runs through the center of the shell in nautilus. The septa are simple in nautilus, while the septa are complex in ammonites. Thus, this summarizes the difference between ammonite and nautilus.

Reference:

1. “Nautilus.” Wikipedia, Wikimedia Foundation, 20 Dec. 2020, Available here.
2. Tharushi Navoda Hathurusinghe. “Unravelling an Ammonite Mystery.” Everything Dinosaur Blog, 4 Aug. 2014, Available here.

Image Courtesy:

1. “Asteroceras BW” By Nobu Tamura – Own work (CC BY 3.0) via Commons Wikimedia

2. “Nautilus Palau” By Manuae – Own work (CC BY-SA 3.0) via Commons Wikimedia