Ammonite fossils are the remains of an extinct group of marine animals known as ammonites. These creatures were once the most abundant animals of the ancient seas and are now a popular subject of study among paleontologists. Ammonites lived during the Paleozoic and Mesozoic Eras, which equates to approximately 408 to 65 million years ago.
The fossils of ammonites are found all over the world and are prized for their mesmerizing logarithmic spiral. These spiral shells were once used for buoyancy and protection from predators. The shells of ammonites are made of aragonite, a crystalline form of calcium carbonate that is also found in pearls and some types of coral.
Ammonites are a distinctive class of extinct invertebrates within the Phylum Mollusca. They are related to the modern pearly nautilus and are excellent index fossils. Linking the rock layer in which a particular species or genus is found to specific geologic time periods is often possible. Their fossil shells usually take the form of planispirals, although some helically spiraled and nonspiraled forms (known as heteromorphs) have been found.
What are Ammonite Fossils?
Ammonite fossils are the remains of ancient marine animals known as ammonoids, which were cephalopods that lived from the Devonian period until the end of the Cretaceous period, about 416 to 66 million years ago. These creatures are related to modern-day squid and octopuses and were once abundant in the world’s oceans.
Ammonite Fossil Definition
Ammonite fossils are the preserved remains of ammonoids, which were marine creatures with a spiral shell that resembled a ram’s horn. These fossils are often found in sedimentary rocks, such as limestone and shale, and can provide valuable insights into the evolution and ecology of ancient marine life.
Ammonite Fossil Characteristics
Ammonite fossils can vary in size, shape, and color depending on the species. They typically have a coiled or helical shell that is divided into chambers separated by walls called septa. The shell is often adorned with intricate patterns and ridges, which can be used to identify different species.
Ammonite fossils also have a siphuncle, which is a tube-like structure that runs through the center of the shell and was used by the animal to control its buoyancy. The siphuncle left behind a distinctive scar on the septa of the shell, which can be used to determine the position of the animal’s body within the shell.
Ammonite Fossil Formation
Ammonite fossils are formed when the remains of the animal are buried in sediment, such as sand or mud, before they can be scavenged or decomposed. Over time, the sediment hardens into rock, preserving the fossilized remains of the animal. The process of fossilization can also result in the replacement of the original shell material with minerals, such as calcite or pyrite, which can give the fossil a different color or texture.
Ammonite fossils are found all over the world and can provide valuable information about the ancient environment and climate in which they lived. They are also popular among collectors and enthusiasts due to their unique beauty and historical significance.
Types of Ammonite Fossils
Classification of Ammonite Fossils
Ammonite fossils are classified based on their shell structure, which can range from smooth to highly ornamented with intricate patterns. The classification system used by scientists is based on the shape of the shell, the number of chambers, and the structure of the sutures, which are the lines where the chambers meet. There are seven main orders of ammonites, each with its own unique characteristics. These orders include the Agoniatitida, Clymeniida, Goniatitida, Prolecanitida, Ceratitida, Ammonitida, and Ancyloceratina.
Different Types of Ammonite Fossils
Within each order, there are many different types of ammonite fossils. Some of the most well-known types include:
- Goniatites – These are the oldest type of ammonite fossils, dating back to the Devonian period. They are typically small and have a simple, coiled shell.
- Ceratites – These ammonites have a distinctive shape, with a long, straight shell that is often ribbed or spiky.
- Ammonites – The most famous type of ammonite, these fossils have a coiled shell with intricate patterns and ridges. They come in a wide variety of sizes and shapes.
- Placenticeras – These ammonites are known for their disc-shaped shells, which are often highly ornamented with spines or knobs.
- Baculites – These ammonites have a straight, elongated shell that is often smooth and unornamented.
Overall, ammonite fossils are fascinating examples of the diversity of life that existed in the ancient seas. With their intricate patterns and unique shapes, they continue to capture the imagination of scientists and fossil enthusiasts alike.
Where are Ammonite Fossils Found?
Ammonite fossils are found all around the world, sometimes in very large concentrations. Scientists have identified more than 10,000 species from fossils found nearly everywhere on the planet where oceans once existed, from the Great Plains of North America to the foothills of the Himalayas.
Global Distribution of Ammonite Fossils
Ammonite fossils are found in rocks that range in age from the Early Devonian to the Late Cretaceous, approximately 416 to 66 million years ago. During this time, ammonites lived in the oceans of the world, and their fossils have been found on every continent.
Ammonites are particularly abundant in rocks from the Jurassic and Cretaceous periods, and they are used by geologists to help date and correlate rocks from different parts of the world. The distribution of ammonite fossils around the world is one of the key pieces of evidence that supports the theory of plate tectonics, which explains how the continents have moved over time.
Ammonite Fossil Localities
Some of the most famous ammonite fossil localities in the world include the foreshore and cliffs at Lyme Regis and Whitby in the United Kingdom, where visitors can find ammonite fossils on the beach and in the cliffs. Other notable sites include the Solnhofen Limestone in Germany, the Pierre Shale in the Western United States, and the Mahajanga Basin in Madagascar.
Ammonite fossils are also found in many other locations around the world, including Australia, Canada, China, India, Japan, Mexico, Morocco, New Zealand, Peru, Russia, and South America. In many cases, these fossils are important for understanding the evolution and distribution of ancient marine life, as well as the history of the Earth itself.
Final Note On Ammonite Fossils
Ammonite fossils are fascinating and provide valuable insights into the history of life on Earth. These extinct marine creatures were once abundant in the oceans and lived for millions of years before becoming extinct along with the dinosaurs at the end of the Cretaceous period.
Ammonites come in a variety of shapes and sizes, and their shells can be found all over the world. They have been used as index fossils, which means that they are useful for dating rocks and determining the relative ages of different geological formations.
Scientists have learned a lot about ammonites by studying their fossils, including their anatomy, behavior, and evolutionary history. They have also discovered that ammonites were not the only cephalopods that inhabited the oceans during the Mesozoic era. Other cephalopods, such as nautiluses, survived the mass extinction event that wiped out the ammonites and the dinosaurs.
While ammonites may be extinct, their fossils continue to captivate scientists and enthusiasts alike. They remind us of the incredible diversity of life that has existed on our planet and the importance of preserving our natural history for future generations to study and appreciate.
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