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INTERESTING PALEONTOLOGICAL INFORMATION
The ammonite creature was very prolific thus, it had diverse patterns of color and a variety of special unique features. Some of these features are sometimes preserved inside or on the surface of the hard shell which fossilized over millions of years.
Horns - Raised Tubercles
In Alberta, there are 3 different species of ammonites found: Placenticeras costatum, Placenticeras intercalare and Placenticeras meeki. These variations of ammonite simply vary in anatomical appearances. For example, the rarer Placenticeras intercalare possesses horns which are protrusions that follow the spiral of the sea creature, whereas Placenticeras meeki has a smooth and flat surface.
Since extensive research about ammonites and ammolite is not conducted very often, our knowledge is limited. Therefore, in some cases, there will be more then one theory to explain irregularities.
Hence, sexual dimorphism is also used to explain horned fossils. Since there were many more females than males in the ammonite world, and about 1:4 horned fossils, it is believed that the fossils with protrusions are in fact males. This also makes sense because in nature males are brighter and more colorful than females. The raised tubercles on Placenticeras intercalare - also called horns, are usually evenly spaced in 2 concentric rings along the spiral from the protoconch out to the edge of the living chamber. It is believed that males had this structure for ornamental and defensive purposes since ammonites were prey to one of the biggest-brained predator of its time; the mosasaur.
In certain pieces of jewelry, these protrusions will appear in the ammolite. However, this phenomenon happens very rarely and the pieces that contain horns are highly valued.
Taken from: http://english.fossiel.net/information/article.php?id=507&/Ammonitida
The organisms in the class Cephalopoda, are all marine organisms such as octopus, squids, nautilus and ammonites. These animals are characterized by a bilateral body symmetry, a head as well as arms or tentacles. Some of them are also composed of an external shell.
The shell of the ammonites consist of chambers joined together by sutures. Moreover, suture patterns have varied forms depending on the subclass of Cephalopods. There are nautiloid, goniatitic, ceratic and ammonitic suture patterns that slightly differ in appearance.
Over millions of years, the suture patterns of the ammonites moved towards a greater complexity. Unlike nautiloids which have "straight" and simple septa, the septa of ammonites evolved very complex undulations which gave greater strength to a thin shell. The contact of these septa with the external shell is called a suture. Sutures are very distinctive and are an important aid in the classification of ammonites.
Oil companies have been known to make use of this factor when core sampling. If an ammonite is found, the soil can be dated since the sutures of a 100 million year old ammonite fossil will differ from a 65 million year old shell.
Suture patterns are not common in jewelry, as they are rarely colored; gemstones with such sutures are highly valued and prized. However, fossils often contain sutures (mostly uncolored).
Click here to access an extensively detailed research paper for more fascinating information about suture patterns.
The chambered part of a Cephalopod shell, like the ammonites, is called a phragmocone. The chambers are divided by septa which make camerae (space between two adjacent septa). The camerae are also linked by a siphuncle which creates buoyancy by gas exchange.
The ammonites grew by adding new and bigger chambers; the largest one found was in Germany (8.5 ft in diameter!). The squid-like part of the animal (soft-body) lived inside the last chamber which was also the biggest. Furthermore, in females the chambers contained the eggs.
When ammonites died, they sunk to the bottom of the sea, where a deep mud bottom engulfed them. The chambers of the shell was then filled with mud, which became hard rock over millions of years.
In some fossils, these anatomical features are not discernible since the preservation of the shell over millions of years was affected. However, in other fossils the chambers are quite discernable and in very few shells, the siphuncle is present. For more information on shell development and anatomical structures, click here.
Mosasaur Bite Marks
During the late cretaceous (70-66 million years ago), a big marine lizard preyed on ammonites. Since ammonites went extinct 66 million years ago, some believe that the mosasaur brought them to the brink of extinction; followed by the K-T extinction, ammonites were wiped off the face of the earth.
As mentioned previously, when ammonites died, they sunk to the bottom of the sea. When a mosasaur bit into an ammonite to crack their shells open and capture the creature inside, the broken shell was left behind and eventually got deposited on the ocean floor. There the shell would sink into the mud and in some cases, intact mosasaur bites on the surface of the shell fossilized.
Mosasaur bites on the ammonite shell can be distinguished by a dark rough spot indented in the shell. See slideshow for examples.
Bite marks are valuable on fossils and can be highly valued. However, it it not often found in jewelry because it is not a desirable characteristic in a gemstone. Click here for a detailed article that dates back to 1960, when bite marks were first being discovered.
The coil of the ammonite shell has often been sought after for it's Feng Shui properties. The spiral also follows the Fibonacci sequence which is endless; therefore, the symbol of infinity is associated with ammonites.
Some fossils have beautifully preserved coils at their center while others may not show any signs of it. There is also two different reoccurring types of coils; an outward coil and the common inward coil.
Fossils that display a spiral will be more highly valued than one that does not contain it.
Membrane Imprint
Some fossils and gemstones contain what resembles a membrane imprint. However, it could also be a soft-body tissue imprint. Nevertheless, these pieces are very rare and are not commonly found. Below are some links to scientific articles and papers if you are seeking for more information on the subject.
Soft-tissue preservation in Jurassic ammonites from Central Russia
Precursory siphuncular membranes in the body chamber of Phyllopachyceras and comparisons with other ammonoids
In some fossils, the ammonite was preserved so that the edge of the shell is almost intact. This feature is preserved rarely and is often sought by collectors. See picture on the right for an example of a beautifully preserved fossil.
Gem Patterns
Since ammolite is an organic gemstone (produced by an organism), various patterns of color exist. It is practically impossible for two stones to be identical. Below are some examples of recurring patterns in ammolite.
Ribbon Patterns
These stones are recognized by a ripple look. They contain multiple lines that sometimes look like sun rays.
Dragonskin Patterns
Dragonskin refers to the scale-like look of the small squares created by fractures. The smaller the squares/fractures, the more valued the gemstone.
Desert Patterns
Similar to the dragonskin pattern, the stones that are classified as desert patterns contain fractures. However, they are wider fractures that to not make small squares. It is titled a desert pattern because they resemble the earth when it dries and cracks.
Mottled Patterns
Earth-like in appearance, these gems contain spots of color.
Crumpled Foil Patterns
As the name suggests, these pieces of ammolite look like crumpled up foil. Good quality gemstones with this pattern will look three dimensional.
Metal Patterns
These stones look like metal sheet; they are smooth and shiny.
Stained glass gemstones are characterized by having see-through qualities when held up.
The first stone is photographed laying down on a white background. The second picture is the same stone, however it is held up.
This third and fourth picture are another example of a stained glass ammolite.
Baculites
These creatures are another extinct cephalopod genus that existed in the late cretaceous. They are considered to be the ancestor of ammonite. Instead of a coiled shell, like ammonites, they have a straight shell. Baculites also contain chambers, camerae and a siphuncle for buoyancy. Cross sections of the shell will resemble a buffalo; for this reason, first nations called ammolite the "buffalo stone."
Baculites are more commonly found with their shell calcitized (with no color). Colored baculite are very rare and highly valued.