Description
Genuine Iridescent Placenticeras whitfieldi Ammonite Fossil
This beautiful fossil ammonite is an iridescent Placenticeras whitfieldi from the Bearpaw Formation of Blaine County, Montana, USA. Dating from the Campanian Stage of the Upper Cretaceous Period, this specimen represents one of the most visually striking types of North American ammonite fossil, prized for its natural colour, marine history, and strong display appeal.
The photo shows the actual carefully chosen specimen you will receive. Full sizing can be seen in the photo. This fossil is a genuine specimen and includes a Certificate of Authenticity lifetime guarantee generic card, making it an excellent addition to a fossil collection, natural history display, educational collection, or gift for anyone interested in prehistoric marine life.
Species: Placenticeras whitfieldi
Placenticeras whitfieldi is a species of ammonite, an extinct marine cephalopod related to modern squids, cuttlefish, octopus, and nautilus. Ammonites lived in coiled shells divided internally into chambers, using the outer body chamber for the living animal while the inner chambers helped with buoyancy control.
This species belongs to the genus Placenticeras, a well-known Late Cretaceous ammonite group recognised for its compressed, disc-shaped shell form. Placenticeras ammonites typically have a relatively flat, streamlined shell with a narrow whorl profile and a smooth to subtly ornamented surface. These features would have suited an active swimming lifestyle in the ancient inland seas that once covered large parts of North America.
The species name whitfieldi honours the American palaeontologist Robert Parr Whitfield, and the genus Placenticeras is widely associated with Late Cretaceous marine deposits across western North America. These fossils are especially desirable when preserved with natural iridescence, as seen in specimens from the Bearpaw Formation.
Natural Iridescent Ammonite Shell
One of the most attractive features of this fossil is its iridescent shell preservation. The shimmering colours are the result of original shell layers and mineralised nacre interacting with light after millions of years of fossilisation. Depending on the angle and lighting, iridescent ammonites can show flashes of red, orange, gold, green, blue, or violet.
This natural colour effect is not painted on or artificially added. It is part of the fossilised shell structure and is one of the reasons Bearpaw Formation ammonites are so sought after by collectors. Iridescent Placenticeras specimens are closely associated with the famous gem-quality ammonites sometimes referred to commercially as ammolite, particularly in deposits of the Western Interior Seaway.
Geology: Bearpaw Formation, Montana
This fossil comes from the Bearpaw Formation, a famous Upper Cretaceous marine rock unit exposed across parts of Montana and the northern Great Plains. The Bearpaw Formation was deposited during the Campanian Stage, approximately 83 to 72 million years ago, when a vast body of water known as the Western Interior Seaway covered much of central North America.
Blaine County, Montana lies within an area where Bearpaw Formation marine sediments preserve a rich record of Cretaceous sea life. These rocks were laid down in offshore marine conditions, including muds, silts, and shales deposited on the seafloor. Over time, the remains of ammonites, bivalves, marine reptiles, fish, and other sea creatures became buried and fossilised within these sediments.
The Bearpaw Formation is particularly famous for its ammonite fauna, including Placenticeras, Baculites, and other Late Cretaceous cephalopods. Fossils from this unit provide an important glimpse into the final chapters of ammonite evolution before their extinction at the end of the Cretaceous Period.
Age: Campanian, Upper Cretaceous
This specimen dates to the Campanian Stage of the Upper Cretaceous Period. The Campanian was a time of warm global climates, high sea levels, and widespread shallow marine environments. In North America, the Western Interior Seaway stretched from the Arctic region southward toward the Gulf of Mexico, dividing the continent into eastern and western landmasses.
Within this seaway, ammonites were highly successful predators and scavengers. They formed an important part of the marine ecosystem, living alongside mosasaurs, plesiosaurs, sharks, bony fish, marine turtles, inoceramid bivalves, and many other organisms. Placenticeras whitfieldi would have inhabited this ancient marine world during the Late Cretaceous, long before the rise of modern mammals and millions of years before humans appeared.
Classification and Fossil Details
Placenticeras whitfieldi is an ammonoid cephalopod within the order Ammonitida. It belongs to the family Placenticeratidae and the superfamily Hoplitoidea, a group of Cretaceous ammonites known for their compressed shells and complex suture patterns. Like other ammonites, Placenticeras had intricate internal shell partitions known as septa, which formed beautiful suture lines where they met the outer shell wall.
The shell morphology of Placenticeras is generally discoidal and involute, meaning the outer whorls overlap much of the earlier whorls. This creates a neat, rounded, wheel-like form that is highly attractive when preserved as a display fossil. On well-preserved examples, the natural nacreous shell surface can remain visible, giving the fossil its distinctive iridescent appearance.
Collector Appeal
Iridescent ammonites from the Bearpaw Formation are among the most desirable Cretaceous fossils from North America. Their combination of scientific interest, natural colour, age, and display quality makes them especially popular with fossil collectors, geology enthusiasts, educators, and natural history buyers.
This Placenticeras whitfieldi ammonite is ideal for display in a fossil cabinet, study collection, office, home, classroom, or museum-style arrangement. Its natural iridescence gives it strong visual appeal, while its geological background connects it directly to the ancient marine environments of Cretaceous Montana.
Authenticity and Presentation
This is a genuine fossil specimen from the Bearpaw Formation of Blaine County, Montana, USA. It has been carefully selected, and the photograph shows the actual fossil you will receive. Full sizing is shown in the photo.
Your fossil includes a Certificate of Authenticity lifetime guarantee generic card, giving confidence that this is a real prehistoric specimen. This iridescent Placenticeras whitfieldi ammonite is a beautiful and scientifically interesting example of Upper Cretaceous marine life, preserved from the ancient Western Interior Seaway and ready to add to your fossil collection.
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