Ammonites are among the most popular types of fossils. They were previously mollusks that looked almost familiar to a squid currently. They had eyes and tentacles while the entire body shape was in a spiral-like form.
The first appearance on earth was around 240 million years ago when they were evolving from being cephalopods. The last trace of these creatures is said to exist about 65 million years ago. Geologists found their traces buried as sediments, and later they became rocks.
It was a sea creature belonging to phylum Mollusca and class Cephalopoda. The external shell is a hard coil. .The outer shell has subdivisions to create several chambers which are separated by walls by the name septum. The hard shell was an adaptation to prevent the animal from getting crushed from any outward force.
The septum further had tough frill like edges in the form of lines which were all unique from each other. The wall was the central area where the shell joined the septum. Although there were many chambers on the body, the ammonite lived in the last and innermost location while the other spaces were full of either gas or liquid.
The materials helped the animal in the movements while in water since it could control the inflow and outflow.
The shell plays a significant role in the animal’s life, the major one being protection. Each of the shells assumed a 360 degrees round shape referred to as a whorl. It comprises of three layers. The innermost layer is a combination of prisms of aragonite, which is a unique form of calcium carbonate.
The middle layer, which is the thickest, is formed by the tiny table like crystals of aragonite. Furthermore, the animal had ribs, spines as well as tubercles, which further protected it through camouflaging to misguide any predators available. These parts also aided in providing strength for feeding and movements.
The animals mostly fed on small vegetations in the sea like planktons. Also, they could feed on any other small animals living at the bed of the sea. A variety of these animals include small crustaceans, corals, bryozoa, or any other floating dead creatures.
The animal first appeared on earth for many years, as stated above in the form of small creatures called barites. Later on, they started evolving into a variety of shapes. Some appear to look like short hairpins. During this process, the animals went through three unfortunate phases that led to their final extinction.
The first occurrence was during the Permian almost 205milion years ago, where only 10 percent survived. During the second phase, nearly 170 million years later, virtually the whole group was wiped away, leaving only one species to survive.
The extinction era is known as the Triassic era, which led to the beginning of the Jurassic era. During the Jurassic, the animals started growing, and the numbers kept increasing. The last phase, which was the most crucial, leading to a complete wipeout of the creatures over the face of the earth, is the cretaceous era. It was the last time any animal in this family appeared.
Additional Readings & Resources
- Ammonite Fossil Collecting – Fossilicious
- Fact Sheet – Nat Geo