 Description:
A magnificent example of an assemblage of the ammonite Discoscaphites
conradi of the Fox Hills Formation deposits of South Dakota. During
the Cretaceous, much of the Western United States was covered by
what is termed the Western Interior Seaway, a broad shallow (100-300
m maximum depth) sea that was home to various aquatic reptiles,
fish, and ammonites. It was open to the North to Canada’s
boreal seas and to the South to what is now the present-day Gulf
of Mexico. During the Late Cretaceous, fluctuations in the sea level
led to various bouts of exposure of some regions; as a consequence,
there is some intertonguing of terrestrial deposits, the most famous
of which is Hell Creek, home of T. rex. Ammonites of this degree
of preservation are difficult to come across singly, much less as
a multiple as seen here. In addition to the complete examples, there
are several partials, numerous bivalves, and a small (12 mm ) gastropod.
The high degree of preservation of their natural mother-of-pearl
shell makes them appear to be preserved as opal. This is a consequence
of light passing through the various layers of aragonite and conchiolin
deposited by the ammonite in life. Conchiolin is secreted by various
other mollusks, including oysters, and is a complex protein. Notice
how the colors change with changing perspective. This is a stunning
example a death assemblage of this flashy ammonite. Some modern-day
cephalopods are known to come together for mating, only to die soon
thereafter. Perhaps this is the fate that befell these beautiful
examples preserved here.
See
more: Ammonites |
