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Ammonite

Ammonites are a group of invertebrates that first appeared during the Devonian Period 345 million years ago.  They are found on every continent and are excellent tools for dating rock.  The creatures actually came near extinction 3 times before finally ending their time on earth in the same event that felled the dinosaurs at the end of the cretaceous period 102 million years ago.  Though much of what is known about ammonites is supposed from the present nautilus species, they are in fact more closely related to the coleoids (squid, octopus, cuttlefish)

Ammonites first began their existence as tiny creatures- measuring only 1mm in size.  They quickly evolved to become much larger- the largest found measures 6.5 feet.  They are sexually dimorphic, meaning the females were often 400% larger than the males.  The shells are comprised of chambers separated by a thin membrane, the shells are secreted by the creature at a rate of about 1 chamber per every 4 weeks, and they lived for about 2 years.  The creatures occupied the largest body chamber and would create new chambers as they grew.  It is supposed that ammonites lived in shallow waters, unlike their cousins the nautilus who live in the deep sea, this is because of their diet, the colorful sutre patterns on their shells, and because their shells often contain ribs and bumps, which would make them poor ocean swimmers.

Ammonites were predatory creatures, feasting on fish, mollusks, and other cephalopods.  They used their tentacles to capture prey and draw them into their jaws located inside their shells.  The chambers inside of their shells contained gasses that would enable them to move about the ocean freely.  They were preyed on by the mossasaurus and other marine reptiles.

Ammonites were given their name by the ram horned God Ammon. During the medieval period they were thought to be petrified snakes, and were often carved with snakes heads.  They were the original discus thrown by the Greeks.  In India ammonites were associated with the God Vishnu, and in Native American cultures they are associated with buffalo and carried for and good health and hunting.

The different types of ammonites we carry are from different places and periods of time.

This pair of ammonites were found in Madagascar and are from the Cretaceous Period 106-112 million years ago.  This pair has been filled with black calcite (most rare!) and had been split in half to reveal beautiful crystallized chambers.

 

 

 

 

 

These are ammonites from the Jurassic Period, found in Russia.  They have been completely replaced by pyrite, cut and polished to reveal druzy chambers.

 

 

 

 

 

 

 

 

This Ammonite is from Madagascar and is one of the oldest species, from the Devonian Period.