 Description:
This is a superbly-prepared specimen of the ammonite Placenticeras
meeki. All the exterior shell has been removed and then polished
to reveal the finest suture detail on on one side of this impressive
ammonite. This genus is characterized by a broad unornamented
disc-like shape. The complex suture pattern, which afforded strength
to the shell at minimum weight is seen here in all its detail.
The reverse still has some of the original shell, which displays
the mother-of-pearl iridescence. This is a consequence of light
passing through the various layers of aragonite and conchiolin
deposited by the ammonite in life. The lack of acidity in the
depositional environment allowed them to be preserved as you
see it here. Notice the play of colors when the viewer’s
aspect changes.
The
Cretaceous Bearpaw Shale formation from which this ammonite originates
outcrops in the United States and Canada, and is famous for many
types of ammonite fossils it contains. See my other ammonite offerings for a large example from Montana which has the shell
removed
from both sides. |
