The Ammonites (Speetoniceras subinversum) - (Reference|Index} Fossils
Ammonites have been known to mankind for thousands of years. They are the source of numerous stories and myths. The name of this spiral-shelled cephalopod originates from the Egyptian god Ammon. Ammon was visualized as a male with the horns of a ram extending from his head. The curled ammonite shells looked like the horns and were called Ammon's Stones or ammonites. Ammonites have actually been understood to humanity for thousands of years. The curled ammonite shells resembled the horns and were called Ammon's Stones or ammonites.
Many cultures throughout history have attributed special powers to this fossil.
In ancient Greece, it was said that if you put an ammonite under your pillow it would cure insomnia and bring good dreams.
If you put a golden ammonite (pryritized) under your pillow you would have prophetic dreams, the Romans thought that.
A Brief History of Ammonites
Ammonites first appeared in the Devonian Period. Early curled species had simple septa with a single arc like the members of the class orthocerida. Ammonites of later durations established septa that had intricate folds called lobes and saddles. They also developed delicate lacey patterns on the outer shell. These patterns together with the shape of the shell and the structure of the septa are how this cephalopod is classified. Ammonites such as Speetoniceras subinversum are very desirable often on auction.
Considering that all living cephalopods (nautilus, octopus, and squid) are predators, we can presume that ammonites were. The only living cephalopod with an external shell is the chambered nautilus. It can swim and manage its depth. It does this by utilizing the siphuncle. The siphuncle is a tube that connects all the chambers in the shell with the living animal. The nautilus can deduct or include gas in these chambers to control buoyancy.
Ammonites have a vast array of size. Specimens have actually been discovered ranging from less than a centimeter to 2 meters in diameter. Early ammonites, until the middle Jurassic, were smaller sized, normally less than 9 inches or 23 centimeters. During the upper Jurassic and lower Cretaceous bigger ranges can be found. Titanites found in the south of England can be over 50 centimeters, 2 feet in size.
The tough shell of the ammonite was quickly fossilized. This, combined with the sheer abundance of this group of cephalopods and its evolutionary period through a number of geologic periods, make it a good index fossil. Index fossils assist geologists and paleontologists to identify the age of rock layers. This is called biostratigraphy. It works like this. If you find an ammonite from a genus known to be from the Triassic Period, then the rock layer it originated from should be Triassic. To be a great index fossil:
It needs to have broad distribution.
There must be a great deal of them.
It needs to come from a group that evolves quickly.
They should be easy to acknowledge.
Ammonites please all wikipedia reference of the above criteria quickly.
Extinction of The Ammonites
The end of the Cretaceous Period was also the end of the ammonites. Dinosaurs and lots of other types of plants and animals passed away out at about this exact same time.
The curled ammonite shells resembled the horns and were called Ammon's Stones or ammonites.
Ammonites of later durations developed septa that had detailed folds called lobes and saddles. The hard shell of the ammonite was quickly fossilized. If you find an ammonite from a genus understood to be from the Triassic Period, then the rock layer it came from should be Triassic. The end of the Cretaceous Period was also the end of the ammonites.