Damon Mcknight
Ammonites, ancient marine cephalopods with distinctive coiled spiral shells, first emerged around 240 million years ago in the Triassic Period. They are now extinct, having disappeared 65 million years ago at the end of the Cretaceous period, coinciding with the extinction of the dinosaurs. Fossils of these fascinating creatures have been found in Australia, with one notable example being the species Australioceras jackii, which is approximately 110 million years old.
| Characteristics | Values |
|---|---|
| First Appeared | 240 million years ago in the Triassic Period |
| Extinction | 65-66 million years ago at the close of the Cretaceous |
| Classification | Ammonoidea subclass with three orders and eight known suborders |
| Structure | Tightly coiled spiral shells |
| Genus | Ends in –ceras, Greek for "horn" |
| Size | 2.6" wide |
| Age | Approximately 110 million years old |
Explore related products
What You'll Learn
Ammonites are ancient marine cephalopods
Ammonites, also known as ammonoids, are a type of ancient marine cephalopod. They first appeared around 450 million years ago, during the Devonian period, and thrived for over 175 million years. They are related to other cephalopods such as squid, octopuses, and cuttlefish, and were early relatives of the modern nautilus.
Ammonites had distinctive, tightly coiled spiral shells, which served as both a protective home and a buoyancy aid. They likely used their squid-like tentacles to capture prey such as crustaceans, bivalves, and fish, and may have avoided being preyed upon themselves by squirting ink, much like modern cephalopods. Ammonites came in a wide range of sizes and shapes, from smaller than an inch to as large as nine feet wide. Some had long, straight shells, while others had helix-shaped or uncoiled shells.
Ammonites were widespread and highly diverse, with over 10,000 species having been identified from fossils found all around the world. They are excellent index fossils, often used to link rock layers to specific geologic time periods. The various species of ammonites lived during distinct time periods that can be easily identified by their suture patterns.
Ammonites mostly died out around 66 million years ago during the Cretaceous-Paleogene extinction event, coinciding with the mass extinction of the non-avian dinosaurs. It is believed that an asteroid impact, ocean acidification, and their small hatchling size all contributed to their demise.
Australia's Founding: A Historical Perspective
You may want to see also
Explore related products
They have distinctive, coiled spiral shells
Ammonites were ancient marine cephalopods, similar to today's squids and octopuses, but with a defining feature: their distinctive, coiled spiral shells. These shells, resembling those of modern nautiluses, served as both a protective home and a buoyancy aid, allowing ammonites to navigate the prehistoric seas with ease. The classification of ammonoids is based in part on the ornamentation and structure of the septa comprising their shells' gas chambers. The suture line (the intersection of the septum with the outer shell) is variably folded, forming saddles (or peaks) and lobes (or valleys).
Ammonites first emerged around 240 million years ago in the Triassic Period and thrived for over 175 million years, adapting through numerous forms and sizes. Their long reign came to an end 65 million years ago at the close of the Cretaceous, coinciding with the mass extinction event that also eliminated the dinosaurs. Ammonites are now extinct, but their distinctive spiral shells have been preserved as fossils, offering a glimpse into the ancient past.
While most ammonites had spiral shells that retained the same shape throughout their lives, there were also heteromorph ammonites, which had uncoiled shells. These heteromorph ammonites likely had a different mode of life compared to their coiled counterparts, as the uncoiled shape would have hindered their swimming speed. The shape of their shells suggests that they occupied a different ecological niche, possibly favouring a more stationary lifestyle or slower, more manoeuvrable movement through the water.
The discovery and study of ammonite fossils, including their unique spiral shells, have provided valuable insights into the evolution and diversity of life on Earth. By examining the structure and composition of these fossils, scientists can learn about the ancient marine environments in which ammonites lived, as well as their ecological relationships with other organisms. The distinctive spiral shells of ammonites have become iconic in the field of palaeontology, serving as a reminder of the vast history and complexity of our planet's biodiversity.
Applying for Australia: A Guide to Your New Life
You may want to see also
Explore related products
They are extinct, like dinosaurs
Ammonites are indeed extinct, just like dinosaurs. Ammonites were ancient marine cephalopods, similar to today's squids and octopuses, but with a defining feature: their distinctive, tightly coiled spiral shells. They first emerged around 240 million years ago in the Triassic Period and thrived for over 175 million years, adapting through numerous forms and sizes.
However, their long reign came to an abrupt end 65-66 million years ago at the close of the Cretaceous period, coinciding with the mass extinction event that also eliminated the dinosaurs. This extinction event was caused by a meteorite strike, which affected ammonites and other life forms in different ways. For ammonites, their restricted geographic distribution may have made them more susceptible to extinction. They were also filter feeders, which made them particularly vulnerable to marine faunal turnovers and climatic change.
While some research suggested that ammonites were already in a long-term, unstoppable decline before the meteorite strike, recent studies have challenged this idea. By assembling a large database of ammonite fossils from the Late Cretaceous and analysing regional variations, scientists found that ammonites were simply experiencing natural selection as they had been for millions of years. In fact, many new species were evolving, and ammonites were thriving in many areas of the world.
Despite their eventual extinction, ammonites played a crucial role in the prehistoric world, and their fossils continue to provide valuable insights into the past.
Applying to Monash University: A Step-by-Step Guide
You may want to see also
Explore related products
They first appeared in the Devonian period
Ammonites are extinct cephalopods characterised by their coiled shells. They are related to the modern-day octopus, squid, and cuttlefish. The first ammonites appeared during the Emsian stage of the Early Devonian period, approximately 419.2 million to 358.9 million years ago. During this time, the southern continents were united into the supercontinent of Gondwana, and the northern landmasses of North America, Greenland, and Europe formed the minor supercontinent of Laurussia or Euramerica.
The Devonian period is often referred to as the "Age of Fishes" due to the diverse and abundant marine life, including the first ammonites, that thrived in the oceans during this time. Ammonites, with their coiled shells, navigated these prehistoric seas with ease, using their shells for protection and buoyancy. They likely fed on smaller marine organisms, capturing their prey with their tentacles.
The first ammonites had straight shells, and over time, their shells evolved into the distinctive tight spiral shape that is commonly associated with them. This transition can be observed through transitional fossils, which show the evolution of their shells from straight to curved (cyrtoconic) and then to a relaxed (gyroconic) spiral before tightening into the familiar form.
The diversity of ammonites was impacted by events during the Devonian period. The Kellwasser Event at the end of the Frasnian age led to a significant decline in ammonite variety, with only a few lineages surviving. However, during the subsequent Famennian age, ammonites rediversified, and their siphuncle structure underwent a radical shift from a lower (ventral) to upper (dorsal) position. Despite this recovery, the Hangenberg Event at the end of the Devonian period nearly wiped out the ammonites, with only a handful of goniatite lineages surviving to become the ancestors of all later ammonoids.
Deadly Australian Wildlife: A Guide to Venomous Creatures
You may want to see also
Explore related products
They became extinct in the Cretaceous period
Ammonites, the ancient marine cephalopods, thrived for over 175 million years, adapting through numerous forms and sizes. They first emerged around 240 million years ago in the Triassic Period and survived three mass extinctions before their reign came to an end in the Cretaceous period, coinciding with the mass extinction event that also eliminated the dinosaurs.
The end-Permian mass extinction had reduced the ammonoids to near extinction, but they survived and became the dominant group of ammonoids in the Late Permian. The end-Triassic extinction event devastated the ammonites, with only a handful of genera surviving and becoming the ancestors of all later Jurassic and Cretaceous ammonites. Ammonites then explosively diversified during the Early Jurassic.
The Cretaceous period, however, marked their end. Ammonites were wiped out during or shortly after the K-Pg extinction event, caused by the Chicxulub impact, about 66 million years ago. This asteroid strike killed off more than three-quarters of all species on the planet. The sudden decline of their main food source, marine plankton, may have been why ammonites couldn't survive the aftermath. Ocean acidification generated by the impact also likely played a role in their extinction, as ammonite larvae were probably small and planktonic and would have been heavily affected.
Ammonites were widespread and highly diverse until the very end of their existence, with at least 57 species belonging to six superfamilies present in the last 500,000 years of the Cretaceous. They are excellent index fossils, helping to date other fossils found in the same layer of marine rock.
Deadly Australian Snakes: A Guide to Species and Survival
You may want to see also
Frequently asked questions
Ammonites were ancient marine cephalopods, similar to today's squids and octopuses but with a defining feature: their distinctive, tightly coiled spiral shells.
Ammonites first emerged around 240 million years ago in the Triassic Period, or around 400 million years ago in the Devonian.
Ammonites went extinct at the close of the Cretaceous period, around 65-66 million years ago, coinciding with the mass extinction event that also eliminated the dinosaurs.
Ammonites had coiled, spiral shells resembling those of modern nautiluses. Their shells served as both a protective home and a buoyancy aid, allowing them to navigate the prehistoric seas with ease.
Ammonite fossils from the Early Cretaceous period, approximately 110 million years old, can be found in Australia. These fossils are from the species Australioceras jackii and are often preserved in association with heteromorph ammonites.
