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AMMONITE FOSSILS FOR SALE
What Did Ammonites Look Like?
Essentially, ammonites looked like squids stuffed into a nautilus shell. It sounds like a crass description, but to the best of our knowledge, it is surprisingly accurate! For the most part, ammonites had tightly spiraled, disc-shaped shells with an exposed soft head and long, grasping tentacles. While most ammonites had circular, spiral shells, a few genera evolved to have straight, loose spiral, paperclip or gyrocone shells. A vast majority of shells are ribbed or have bumpy protuberances. The exact function of these bumps is currently unknown, but they certainly add intriguing character to an already fascinating creature.
Why Are Ammonites Such Popular Fossils?
Ammonites just happened to have the “right stuff” to maintain their lineage throughout a wide range of habitats and over a span of nearly 200 million years. Because of their prevalence throughout the Paleozoic and Mesozoic age, rapid evolutionary radiation, and their calciferous shell compositions, they make excellent candidates for fossilization and are a useful tool to properly age geologic formations.
A major facet of why ammonites are so prevalent in the fossil record is that they lived in shallow seas and spent their lives near the ocean floor, where they inevitably settled as they died. The composition of the seafloor was such that sediments and bacteria quickly enveloped a dead organism, leaching oxygen from the sand, thus concreting the shell and preserving it. Depending on the mineral composition of the sand in which the ammonite fossilizes, gnarly pockets of calcite crystals and agate can form inside their shells! These specimens are amazing when bisected and polished.
How Big Were Ammonites?
Ammonites had a wide range of sizes that varied depending on location and prey preference. Some of the smallest ammonites measure less than an inch long, opposed to the largest, which could reach diameters of almost 3 meters (9 feet). These ginormous species have been found in Europe and Mexico, painting an interesting picture of the resource availability in both locations to allow for such incredible growth.
The world's largest ammonite fossil, a 5.9 foot wide specimen of the species Parapuzosia seppenradensis at the Museum of Natural History in Münster, Germany. Had its living chamber been found complete, could have been as much as 8.4 feet wide. Creative Commons License
The most popular ammonites that circulate through the general public and the scientific community are in the range of 1 inch to a foot in diameter. As with most animals, availability of resources is a limiting factor in growth, which is why certain species at specific locations are smaller or larger than their compatriots. For example, many of the ammonites from Madagascar are found in a huge variety of sizes. Red flash ammonites of the genus Cleoniceras are only a couple of inches across, but were swimming in the same seas as the colossal Kranosphinctites ammonites that were almost 2 feet in diameter and had large, knobby bumps around the outer whorls of their shells.
Why Do Some Ammonites Have Squiggles On Their Shells?
The squiggly lines you see on ammonite fossils are sutures. All ammonites have these markings on their shells, though they aren't always visible. These lines are only on the inner shell and demarcate where the septa divides the ammonite’s shell into individual chambers. They are only visible when the protective outer layer of the shell is removed or broken during the extraction process. They are an important characteristic that allow paleontologists to differentiate between the different ammonite species.
As ammonites evolved through the ages, suture patterns tended to become more and more complex. There are three higher classifications of suture lines: goniatite, ceratite and ammonite. The patterns and complexity of the lines increase across the types. The names refer to the Ammonoidea order, where the style of line originated and evolved from.
A polished Cleoniceras
ammonite fossil from Madagascar showing a particularly well-defined suture pattern.
How Did Ammonites Swim?
To answer this question, it is important to understand how an ammonite maintains vertical buoyancy. Most ammonites, with the exception of a few select species, have a tube that runs along the outer edge of the whorls throughout the entirety of the shell, called the siphuncle. The purpose of the siphuncle is to control buoyancy by diffusing gas in water and blood into various chambers of the shell. The exchange of gas, completed via osmosis, allowed the animal to maintain its vertical position as it floated through the water. Unfortunately, the method of propulsion used by ammonites is unknown as it was part of the soft body that did not preserve. However, due to their relation to squids, many scientists propose that the most likely form of locomotion was achieved through the use of a siphon that blasts jets of water.
A team of scientists in Utah are working to understand how ammonite shell shape factored into their movement and thus far it is safe to assume that with their large buoyant shells and potential siphon they were apt to drift through the ocean like a zeppelin or hot air balloon rather than a jet fighter. Because the siphon was probably forward facing, ammonites most likely propelled themselves backwards through prehistoric seas. This paints an interesting picture about how ammonites hunted: backward propulsion does not an effective pursuit predator make. Therefore we are left with two major possibilities for feeding strategies: lurking for ambush or scavenging and scraping the ocean floor. Both of these strategies are feasible among cephalopods: the modern nautilus scavenges the ocean floor for buried organisms and carcasses and lurking ambush is a feeding strategy employed by many marine species that can be quite successful. However they swam, they were able to continuously adapt to a changing world for nearly 200 million years.
Ammonites Through The Ages
Ammonites were common throughout shallow seas from the Devonian in the Paleozoic era to the end of the Cretaceous and the conclusion of the Mesozoic era. Over this span of time they went through multiple periods of species radiation after hitting the edge of extinction. With each successive near collapse, they came back with slightly different body plans to fill new niches and prevail in a tumultuous environment. This strategy seemed to work out well for ammonites as a whole and may be indicative of the current radiation of modern cephalopods.
Why Are Some Ammonite Shells Straight?
Though the majority of ammonites have spiraling disc-like shells in a growth plan referred to as plainspiral, many other shell shapes arose at various points in ammonites' evolutionary journey. Species of ammonites with shell shapes different from the plainspiral are called heteromorph ammonites. The Cretaceous genus Baculites is a prime example: they were known for their straight shells, but were otherwise similar to other ammonites in every other way.
Heteromorphs provide an important glimpse into the specialization of a group of animals over a relatively short amount of time. Typically straight-shelled, paper-clip, or coiled shell ammonites were less buoyant than their plainspiral relatives. This is similar to how a pumpkin will float better than a zucchini squash. Scientists have conjectured that these ammonites may have spent more time combing the seafloor for nutrients than their more buoyant, disc-like, plainspiral relatives. Heteromorph ammonites belonging to the suborder Ancyloceratina, first appearing in the late Jurassic, but it wasn’t until the Cretaceous that heteromorph species really took off in popularity. Just why these wacky shell shapes evolved is still up for debate. Maybe they were a type of defensive adaptation or the need for a less buoyant shell was necessary to more easily rake the ocean floor for food. Either way, they look awesome and will continue to enamor paleontologists until the next illuminating discovery.
What Did Ammonites Eat?
The majority of paleontologists agree that an ammonite's diet was probably very similar to that of modern cephalopods. A wide array of undersea critters are common prey items for cephalopods, including fish, clams, crustaceans, and other invertebrates like sea stars. These were likely susceptible to predation by ammonites in the Paleozoic and Mesozoic seas. Recent technological advances yielded in-depth, three-dimensional reconstructions of ammonite mouth parts that have provided insight into how and what ammonites of the genus Baculites snacked on This research revealed that these ammonites had mouthparts best suited for capturing and consuming plankton and other organic debris. This supports another popular theory that ammonites scavenged the seafloor for biological particulates and trilobites in the early years of their existence.
What Snacked On Ammonites?
What were the biggest consumers of ammonites? The answer seems too simple: marine reptiles, particularly mosasaurs. Both species were extremely diverse and prevalent, especially in the Cretaceous. It makes sense ecologically that both species would be so successful. Typically, when one of two linked species does well, they both thrive. The food chain runs on natural balance and this relationship is proof of how true that can be. This feeding relationship is evident in ammonite shells that bear bite marks that perfectly fit mosasaur teeth. On the other hand, many mosasaur species evolved teeth that are excellent for crushing shells. Granted, other shelled marine creatures lived with mosasurs, but the prevalence of both ammonites and mosasaurs in overlapping habitats and depth limitations seem to point in a direction that favors this predator-prey relationship.
An ammonite fossil from Alberta, Canada preserved in ammolite with circular bite marks from a large mosasaur.
A team of researchers based in England concluded in 2010 that bite marks observed on some ammonite shells are consistent with what you would observe from the indentation left by a beaked cephalopod. The location of the puncture is consistent with the area where the muscles that extend the ammonite’s soft body from its shell would be located. The researcher’s paper argues that the precision and intelligence needed to make a bite of that order is highly unlikely from most fish and reptiles. They postulate that the most likely candidate would be a squid-like creature that could manipulate the ammonite via arms and tentacles before delivering a crippling bite that forces the soft parts of the ammonite out to be consumed.
Other researchers throughout the years have posited that the triangular holes in ammonite fossils indicate the presence of limpets feeding on algae attached to the cephalopod’s shell. A limpet is a type of marine snail that creates a powerful suction with its mouth and attaches to whatever it is feeding off of in a mutualistic relationship. This suction is quite powerful; some researchers have compared it to an organic magnet. Paleontologists have long suggested the holes in ammonite shells resemble the impression of a limpet’s mouth, though other theories relating to mosasaurs and beaked cephalopods are now more widely accepted.
Why Are Some Ammonites Shiny Or Iridescent?
The fossilized shells of many ammonites are iridescent due to the mineralization process as they fossilized, but they would not have had iridescent shells while alive. This optical illusion is a result of ammonite shells' high content of a substance called nacre. Because ammonite shells are composed of calcium carbonate (aragonite) and nacre is a layered, plate variety of aragonite, their shells and especially their inner shells tend to present iridescence. It can also manifest as pearlescence, similar to the mother-of-pearl inner shells of modern shellfish. Iridescence and pearlescence are achieved as thin sheets of aragonite reflect and fracture light at a width most similar to the wavelength of visible light it presents. Thicker sheets produce reds and oranges and thinner sheets reflect blues and purples. As you might expect, thinner sheets are more fragile and don’t preserve as well, which adds to the rarity of specimens that flash this color.
An ammonite fossil from Madagascar displaying some particularly flashy red iridescence.
What’S The Difference Between An Ammonite And An Ammolite?
This is a fairly common question that has a straightforward answer. All ammolite comes from ammonites, but not all ammonites have ammolite. Ammolite is a rare, opal-like gemstone composed of the shells of fossil ammonites found in Southern Alberta, Canada. Ammolite is world famous for its intense iridescence that presents vivid hues of red, orange, yellow, green, blue, and purple flashes. These fossils exhibit phenomenal color play that shifts as you change the angle of the shell to a light source. Ammolite of exceptional quality is quite rare and makes for stunning jewelry and display pieces.
An ammonite composed entirely of ammolite. Complete specimens of this quality are rare and prices run into the tens or even hundreds of thousands of dollars. Creative Commons License
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