Cymatoceras
Nautiloid
Phylum
Mollusca, Class Cephalopoda, Subclass Nautiloidea, Order Nautilida,
Family Cymatoceratidae
Geological
Time: Cretaceous
Size (25.4mm=1
inch): 75 mm diameter
Fossil
Site: Tulear, Madagascar
Fossil
Code: PP18
Price:
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 Description:
A spectacular nautiloid fossil from Madagascar which has been sagitally
split and polished to show wonderful detail within. Most of the
individual chambers are open and filled with rose and beige Calcite
crystals, with the septa (divisions) between each chamber preserved
as beige Calcite, making for a superb display piece. The primitive
suturing pattern distinguishes these cephalopods from the ammonites
(I have posted it with the ammonites as they are close relatives).
Additionally, they have the siphuncule at the center of the chambers
as opposed to the top as in the ammonites. It is visible here as
the spiral seen in some chambers. The Nautilida have a rich  evolutionary
history which began in the early Devonian. The order suffered a
drastic decline in the late Devonian, only to have an extensive
radiation in the Carboniferous. They suffered less than some other
orders at the end of the Permian, and did better than the ammonites
by surviving the Cretaceous extinction, leaving one descendant,
the modern-day Nautilus, of which there are 5 species. Nautiloids
had stronger shells than the ammonites, and were capable of descending
deeper than the ammonites could. Perhaps this allowed them to survive
the disaster at the end of the Cretaceous. Many of the chambers
are not completely infilled with Calcite, lending a geode-like appearance
to the specimen. This is a fine example of a nautiloid from the
Cretaceous deposits of Madagascar, one that is sure to be a fine
addition to any collection. |
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