Ammonites are an extinct group of cephalopods that entered the fossil record 400 million years ago.  They survived several mass extinction events, including the Permian–Triassic "Great Dying" which wiped out 96% of all marine species.  They finally succumbed during the Cretaceous-Paleogene extinction event 66 million years ago, which also wiped out the dinosaurs. 

This specimen is a fossilized Perisphinctes ammonite shell from Madagascar. These Jurassic era creatures are not only beautiful, but important index fossils as well. The shells are over 150,000,000 years old and were originally made of calcium carbonate before being fossilized. Their assisted the fossilization process, meaning they are perserved in excellent detail.

Each Natural Ammonite is packaged in a sturdy shipping container. A small informational card that serves as certificate of authenticity is also included.

Fossils range in size between 1.5 and 2.5 inches and you can expect to see variation in color from white to sandy.

These ammonites are quite large and the perfect size to hold in your hand. You can feel each turn of the spiral as you study the construction of the amazing shells. They will delight any visitor and are perfect for display in every setting.

We also have polished ammonite fossils and our classic riker box sized ammonites in the shop as well. Check out all our ammonites at the collection below!

ESTIMATED AGE : c. 150,000,000 years old

Ammonites are an extinct group of cephalopods which entered the fossil record 400 million years ago. They survived several mass extinction events, including the Permian–Triassic "Great Dying" which wiped out 96% of all marine species. They finally succumbed during the Cretaceous-Paleogene extinction event 66 million years ago, which also wiped out the dinosaurs.

The size of ammonite shells range from sub-centimeter dwarf species to giants nearly three meters in diameter. Most iconic shells exhibit a nearly perfect logarithmic spiral.

This ammonite is from the genus Perisphinctes, which lived over 150 million years ago during the Jurassic period. Like other ammonites, Perisphinctes serves as an invaluable index fossil, allowing scientists to estimate the age of the geological layer in which they are found. This type of ammonite can be found all over the world. The fossils in our collection come from Madagascar and lived in the seaway growing between the island and the paleocontinent Gondwana.

Perisphinctes mostly swam in shallow waters, such as in the Tethys Ocean that formed when the Pangea supercontinent split into Laurasia and Gondwana. While the large-shelled ammonite may give the appearance of a slow bottom feeder, they were actually ferocious predators that navigated the waters easily, owing to gas chambers in their shells that allowed them to maintain buoyancy. By shooting jets of water from their bodies, they could move quite quickly through the Jurassic seas to hunt prey.

Ammonites were an incredibly diverse and plentiful group of animals that survived for hundreds of millions of years and lived all across the planet. The group also underwent rapid evolution and specialization, and their rocky shells means there are many different and identifiable species in the fossil record. Because of this, scientists can use them to easily identify the age of other fossils and geologic deposits found in the same layer of the ammonites. They're a welcome sight to the eyes of any inquisitive geologist!

How these creatures lived is of intense interest to science, as ammonites likely played a vital role in the food chain in the ancient seas. Evidence exists to suggest that ammonites were a prime food source for Mosasaurs and fishes, while other studies suggest the bite marks on their remains were created after death by limpets or even by other cephalopods.

Many thousands of distinct species make up the long-lived ammonoid subclass.  Though most ammonite shells are the classic spiral, there are also straight and gastropod-like shells and even some shells that are partially uncoiled.  The surface of the shells also vary quite widely, from smooth to wildly thorny.

Ammonites were an incredibly diverse and plentiful group of animals that survived for hundreds of millions of years and lived all across the planet. Their rapid diversification and tough, rocky shells means there are many different and easily identifiable species in the fossil record. Because of this, scientists can use them to easily identify the age of other fossils and geologic deposits found in the same layer of the ammonites. They're a welcome sight to the eyes of any inquisitive geologist!

Aside from their complex shells, there is little direct evidence regarding the appearance of ammonites due to the absence of soft tissue fossils. However, many scientists believe ammonites had bodies similar to that of the present-day Nautilus.

Ammonite shells grew in a natural spiral and made a consistent, mathematically significant pattern. This special shape is known as a logarithmic spiral.

The main property of a logarithmic spiral is that the shape of the spiral is unaltered as it increases in size. Each turn is a pure geometrical progression of the last with a common ratio.  This form is found in many natural phenomena, from the shape of galaxies to patterns on sunflower heads.