4.6" Fossil Ammonite (Placenticeras) - South Dakota

This is a 4.6" ammonite (Placenticeras) from the Fox Hills Formation of South Dakota. It has been wonderfully prepared on the hard concretion it was found in. The ammonite is iridescent on the back side, while the front shows the intricate suture pattern of the inner shell.

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 meeki
LOCATION
South Dakota
FORMATION
Fox Hills Formation
SIZE
4.6", 4.9" total height
ITEM
#115136
GUARANTEE
We guarantee the authenticity of all of our specimens.