Ammonites and belemnites, two groups of cephalopods that lived during the Mesozoic era, are known for their flat sides, coiled shells, and tentacles that surrounded beak-like jaws. The fossils of these mollusks can be found in rocks rich in ammonite fossils, and they were named after the Egyptian god Ammon and the Greek word for darts, respectively.
In this article, we will take a closer look at these fascinating creatures, their physical characteristics, and their place in history.
What are Ammonites and Belemnites?
Ammonites and belemnites are both groups of cephalopods that lived in the sea during the Mesozoic era, between 252 and 66 million years ago. Cephalopods are mollusks with soft bodies, which include nautiluses, octopuses, and squid. These creatures had tentacles that surrounded beak-like jaws and used jet propulsion to move in the opposite direction by squirting water.
The shells of ammonites and belemnites are different from those of other mollusks in that they are flat-sided and coiling. The shell of an ammonite has a spiral structure that is divided into chambers separated by septa. The shell is coiled to provide buoyancy and to enable the creature to move up and down in the water column.
In contrast, the belemnites have a bullet-shaped internal shell, known as the guard, which is made of calcium carbonate. The guard was pointed on one end and had a broad, flat end on the other, which allowed the creature to balance in the water.
Distribution and Fossilization
Ammonites are widespread and abundant fossils, and their remains can be found all over the world. They lived in various marine environments, such as shallow coastal waters and deep ocean basins. The fossilization process of ammonites and belemnites is unique because of their hard shell, which is resistant to decay.
When the animal dies, the shell sinks to the sea floor and gets covered by sediment. Over millions of years, the sediments compress the shell and create a fossil.
Despite their abundance during the Mesozoic era, neither ammonites nor belemnites survived beyond the Age of Dinosaurs. The cause of their extinction is uncertain, but it is believed that a combination of factors, such as climate change, competition for resources, and predation, may have contributed to their decline.
Importance of Ammonites and Belemnites
Ammonites and belemnites are important to paleontologists and geologists because they provide insights into the history of life on Earth. They are index fossils, which means that they can be used to date rocks and determine the age of geological formations. Ammonites are also used to study the evolution of cephalopods and their relationships to other organisms.
Ammonites and belemnites are fascinating creatures that lived millions of years ago, and their fossils provide us with valuable information about the history of life on Earth. Their physical characteristics, distribution, and extinction tell us about the changes in the marine environment during the Mesozoic era.
As we continue to study these creatures, we may discover more insights into the evolution of life on our planet.