Fossil Ammonites (Hoploscaphites & Sphenodiscus) - South Dakota

This is a 4.2" wide rock nodule that contains a JHoploscaphites (Jeletzkytes) spedeni ammonite and a small Sphenodiscus lenticularis ammonite, collected from the Fox Hills Formation of South Dakota. The largest ammonite is Jeletzkytes spedeni and it measures 3" wide. A wide variety of complete and fragmented shells can also be found throughout the rock.

There is a repaired crack through the largest ammonite and through what remains of the surrounding rock.

These 70 million year old ammonites lived when South Dakota was a shallow inland sea. They were found preserved in concretions when split open. They then had to be hand-prepared to remove the hard rock surrounding them from their shells, a very time consuming task.

Ammonites were predatory cephalopod mollusks that resembled squids with spiral shells. They are more closely related to living octopuses, though their shells resemble that of nautilus species. True ammonites appeared in the fossil record about 240 million years ago during the Triassic Period. The last lineages disappeared 65 million years ago at the end of the Cretaceous.

What an ammonite would have looked like while alive.
What an ammonite would have looked like while alive.
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DETAILS
SPECIES
Hoploscaphites (Jeletzkytes) spedeni & Sphenodiscus lenticularis
LOCATION
North Central, South Dakota
FORMATION
Fox Hills Formation
SIZE
Jeletzkytes ammonite 3" wide on 4.2 x 3.4" rock
ITEM
#137273
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