Great South Gems & Minerals

• Ammonite (Madagascar) •

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• Ammonite (Madagascar) •

ammonites - ammonite fossils - parapuzosia seppenradensis

Geologists and paleontologists have used the extinct cephalopod ammonite as an index fossil in dating a particular rock layer, as the ammonites are so wide-spread and abundant worldwide and different species existed over an extremely long period of time. Ammonites existed from the Silurian period, about 400 million years ago, all the way up until the end of the Cretaceous period which ended about 65 million years ago. A period of over 300 million years! And, during this extremely long period of time ammonites were extremely abundant. Many genera evolved and ran their course quickly, becoming extinct in a few million years. Due to their rapid evolution and widespread distribution Geologist and Paleontologist can date a rock layer based on the particular species of ammonite found in the strata.

Ammonites started out as babies with tiny button-like shells and as they grew they made consecutive chambers to their shell. And what's interesting is, as the animal grew, made an addition to it's shell, it would move into the now larger shell section and seal off the old smaller chamber section. Scientist believe that the ammonite would fill the closed-off chamber with a type of gas. This enabled the ammonite to float and therefore be a free-swimming animal. Many illustrations of the ammonite show the larger section of the animal at the top, probably for aesthetic reasons, however this an incorrect presentation. The smaller shell section would have been filled with gas and therefore would have floated above the larger sections.

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Ammonites were predators much like the modern cephalopods, the squid and octopus. The ammonites had tentacles in which it could grasp it's prey and sharp beak-like parts at its mouth. It is believed that the ammonites fed on fish and crustaceans.

According to "Wikipedia, the free encyclopedia" most ammonites were in the one inch to about nine inches diameter range. However, ammonites have been found with a diameter of 6.5 feet! This giant of an ammonite is the species Parapuzosia seppenradensis, from the Cretaceous period of Germany. The largest documented North American ammonite found is the Parapuzosia bradyi from the Cretaceous Period measuring 4.5 feet in diameter.

While most ammonites had rounded spherical shells, there is a species coming from China that has a partial rounded shell at its base or beginning end, and then the ammonite abandoned the rounded shell type to forms a straight shell much like the Orthoceras. Ammonite fossils have been found world-wide.

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