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Goniatites are an extinct group of ancient marine animals which evolved from the nautiloids during the early in the Devonian period some 400 million years ago. They became extinct during the Permian period.
The goniatites are classified as ammonoids, which is an extinct group.  The ammonoids are part of a larger group, cephalopods, which includes belemnites and nautiloids.  The cephalopods are part of a larger group of animals called the molluscs, which includes bivalves and gastropods.
The goniatites all possessed an external shell, which is divided internally into chambers.  The animal lived in the largest external chambers and the internal chambers would have been filled with gas making the animal buoyant in the water. The general structure of the goniatites would have been similar to that of their relatives the ammonites, being a free swimming animal possessing a head with two well developed eyes and tentacles.  To learn more about ammonites, along with belemnites and nautiloids, just click on the appropriate icon below. 
Goniatites are small to medium in size often less than 15 centimeters in diameter (6 inches).The shell is always coiled, unlike that of the later ammonites of the Mesozoic era who, some of which evolved into partially coiled or completely uncoiled forms. The shape of most goniatite shells suggests that they were poor swimmers. 
The thin walls between the internal chambers of the shell are called the septa, and as the goniatite grew it would move its body forward in the shell secreting septa behind it, thereby adding new chambers to the shell.  The sutures are visible as a series of narrow wavy lines on the surface of the shell.  The sutures appear where each septa contacts the wall of the outer shell.
A distinctive feature of the goniatites is the “zigzag” pattern of their sutures.  The sutures of nautiloids are, by comparison, somewhat simpler; being either straight, or slightly curved.  A goniatite displaying characteristic “zigzag” sutures is shown here.  

Goniatites are found in North America, Europe, North Africa and Australia.  Certain limestones in western part of the Republic of Ireland are packed with beautifully preserved goniatite fossils.  They are also found in marine bands of the Carboniferous 
Coal Measures in Europe and in marine rocks of the Pennsylvanian period in Arkansas. Large numbers of goniatites occur in rocks from the Devonian period of Morocco, and they are important zone ,or index fossils,  used  by geologist in dating the rocks of that period.  To learn more about geology, just click on the icon below.

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