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Split Cymatoceras Nautiloids from Madagascar

Description: Spectacular nautiloids from Madagascar which have been sagitally split and polished to show wonderful detail within. Most of the individual chambers are filled with Calcite crystals of various colors, with the septa (divisions) between each chamber preserved as contrasting 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.
Name: Nautilida; Cymatoceras
Age: Cretaceous
Location: Tulear, Madagascar

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