Ammonites disappeared about 66 million years ago, during the mass extinction event of the Cretaceous-Paleogene period. This extinction was caused by a combination of factors, including the impact of a meteorite, climate change, and massive volcanic eruptions.
During the Cretaceous period, the Earth experienced a sudden change in climate: global temperatures plummeted, oceans became colder, and sea levels dropped. It may not seem significant, but this cooling caused a shift in ocean currents and their chemical dynamics. The result: less availability of oxygen, a crucial factor for the survival of ammonites. They simply couldn't adapt quickly enough to these new living conditions. Not great when your entire existence depends on a precise balance. These rapid climate upheavals also affected their food: plankton, the basis of their diet, was directly impacted by these changes. Thus, with less food and difficult conditions, extinction was guaranteed.
Ammonites were a kind of luxury marine fast food for a few particularly effective predators, including mosasaurs, formidable marine reptiles of the Cretaceous. With their rather impressive spiral shell, ammonites seemed protected, but against such powerful jaws, it was a lost cause. These new predators had developed remarkable abilities: speed, agility, and more sophisticated attack strategies. As a result, ammonites found themselves at the front line of the menu, becoming easy prey as predator pressure drastically increased towards the end of the Cretaceous. This constant predation likely weakened their ability to reproduce and survive in the long term, accelerating their already initiated decline.
At the end of the Cretaceous period, a large asteroid crashed near present-day Mexico (Chicxulub crater). This gigantic impact caused tsunamis, fires, and especially sent a huge amount of dust and gas into the atmosphere. As a result, sunlight was greatly reduced and the climate abruptly cooled. This catastrophe seriously disrupted marine ecosystems by destroying the foundations of the food chain, notably plankton, on which ammonites directly depended. Deprived of sufficient food and unable to adapt to these sudden changes, they ultimately disappeared completely.
Ammonites found themselves in direct competition with rising marine species, particularly bony fish and the ancestors of modern cephalopods (such as squids). These newcomers were much more efficient and adaptable in their hunting, occupying the same food niches as the ammonites. Gradually, ammonites lost ground, lacking sufficient food resources. Starved and disadvantaged compared to their highly competitive new neighbors, they began to decline progressively. Their competitors were less demanding in terms of habitat, more agile, and often equipped with anatomy better suited for the active pursuit of prey — in short, a fatal combination for the ammonites.
Fossilized ammonite shells were once used as talismans and jewelry in certain ancient cultures, reflecting their enduring fascination throughout history.
Even though ammonites disappeared at the same time as the dinosaurs, their close relative, the nautilus, still survives in today's oceans.
Some fossilized ammonites exhibit complex patterns known as suture lines, which are useful for identifying species and understanding their evolutionary processes.
Ammonites are often used as guide fossils by geologists, as their rapid evolution allows for precise dating of the period of the rocks in which they are found.
Ammonites were marine mollusks belonging to the class of cephalopods, close relatives of modern squids and octopuses. They had a coiled, spiral shell and lived in the oceans during the Mesozoic era, until their extinction about 66 million years ago.
Ammonites were sensitive to temperature fluctuations, ocean acidification, and the depletion of food resources, all of which were environmental factors that contributed to their gradual extinction over time.
The shell of ammonites, made of calcium carbonate, easily fossilized under specific conditions. Their wide distribution in ancient oceans, as well as their very long existence on Earth (over several million years), explains why their abundance of fossils provides us with so much information about their evolution and extinction.
Researchers primarily study fossils found in geological layers. The analysis of isotopes, paleoclimatic studies, and the identification of major geological events allow us to examine the likely reasons for their extinction. The most widely accepted theory today links their disappearance to the mass extinction event at the end of the Cretaceous, notably caused by the impact of a meteorite.
Ammonite fossils are common due to their past abundance, the durable nature of their limestone shells, and the favorable conditions for their fossilization in marine sediments.
No, there are no direct descendants of ammonites today. However, their distant relatives, such as nautiluses, squids, and octopuses, share their common cephalopod ancestors.
Ammonites have no living direct descendants today as they have completely disappeared. However, their distant relatives such as squids, octopuses, and nautiluses still exist today.
Yes, the impact of an asteroid 66 million years ago, which notably caused the extinction of the dinosaurs, also had a significant impact on the ammonites. The global climate upheaval that followed this event contributed to their complete disappearance.
Yes, ammonites lived during the Mesozoic Era, known as the 'Age of Dinosaurs.' Although they inhabited distinct aquatic environments while dinosaurs predominantly occupied the land, both groups evolved and coexisted on Earth until their joint extinction at the end of the Cretaceous period.
Ammonites were marine cephalopods with spiral shells that were widespread in prehistoric oceans, having lived between approximately 400 million and 66 million years ago. They are close relatives of today’s octopuses and squids.
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