3.9" Cretaceous Ammonite (Placenticeras) Fossil - South Dakota

This is 3.9" wide Placenticeras costatum ammonite fossil that was collected from the Pierre Shale of South Dakota. The beautiful suture pattern of this ammonite can easily be seen on the surface. It comes with an acrylic display stand.

About Ammonites

Ammonites were ancient marine cephalopods, similar to today's squids and octopuses, but with a defining feature: their distinctive, tightly 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. First emerging around 240 million years ago in the Triassic Period, ammonites thrived for over 175 million years, adapting through numerous forms and sizes. As predatory creatures, they likely fed on smaller marine organisms, using their tentacles to capture prey. However, 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.

What an ammonite would have looked like while alive.
What an ammonite would have looked like while alive.

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DETAILS
SPECIES
Placenticeras costatum
LOCATION
Cheyenne River, South Dakota
FORMATION
Pierre Shale
SIZE
3.9" Wide
ITEM
#113161
GUARANTEE
We guarantee the authenticity of all of our specimens.