Cymatoceras
Nautiloid
Phylum
Mollusca, Class Cephalopoda, Subclass Nautiloidea, Order Nautilida,
Family Cymatoceratidae
Geological
Time: Cretaceous
Size (25.4
mm = 1 inch): 63 mm across by 47 mm tall
Fossil
Site: Tulear, Madagascar
Fossil
Code: PP25
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Description:
A spectacular nautiloid from Madagascar which has been sagitally
split and polished to show wonderful detail within. Most of the
individual chambers are open and filled with brown Calcite crystals,
with the septa (divisions) between each chamber preserved as
light brown 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).
This one shows the suturing well from the interior while the
exterior shows some or the pearlescent natural shell, making
it a striking piece. 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. 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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