Gonioclymenia Ammonite Goniatite Fossil XL Sea Shell Prehistoric Devonian Collection (2)

Ammonite Goniatite XL Fossil Seashell mm 95 x 77 x 30 gr 250 Gonioclymenia speciosa Extinct Prehistoric Cephalopods Molluscs Paleozoic Devonian Collecting Paleontology Museum, only a piece, as in photos.

Pleasant fossil collectible find of Goniatid Ammonite from the Upper Devonian, polished on worked matrix, with clear details of the spirals and suture lines well preserved.
Only a piece, as in photos.

The Goniatids (gen. Goniatites) are extinct Ammonites, shelled Cephalopods, belonging to the order Goniatitida, family Goniatidae. This originated from more primitive Anarcestida Agoniatitida Ammonites in the Middle Devonian period about 390 million years ago.
Having survived the extinction of the Late Devonian, the Goniatites flourished during the Carboniferous and the Permian until the extinction in the end of the Permian about 250 million years ago. Survived only their fellow Ceratites, indirect descendants of Anarcestida.
Even Goniatites possessed a shell internally divided into rooms. The animal lived in the largest last room, while the other internal chambers would have been filled with gas, making the animal buoyant in water.
The shells of Goniatites are small to medium in size, almost always less than 15 cm (6 inches) in diameter and often smaller than 5 cm (2 inches) in diameter. The shell is always wound in a flat spiral, unlike that of ammonites of the Mesozoic in which some are trochoidal and even aberrant (heteromorphs). The shape varies from broad-thin disc-shaped to wide globular and may be smooth or distinctly ornate. Their shape suggests that these cephalopods they were bad swimmers.
The suture lines, corresponding to the internal septa, are visible as a series of narrow wavy lines on the surface of the outer shell.
The typical goniatite has a suture with saddles and smooth lobes, which gives the name of "Goniatitic" for this particular suture pattern. In other cases, it has a distinctive "zig-zag" pattern. More recent species showed suture patterns of increasing complexity. One explanation is that this would lead to an increased resistance of the shell.
Due to the lack of clear indications of the kind of life they led (nektonic, planktonic, demersal, planktivorous, piscivorous), it is unclear what their food resources, lacking even a mouthparts adapted to crush the shells.
Goniatites fossils have been found in North America, Europe, North Africa and Australasia, in areas which at the time were tropical or subtropical. In Ireland may be found beautifully preserved fossils. A large number of Goniatites also arise from the rocks dating back to the Devonian of Morocco, making it an important stratigrafic index used to date rocks of that period.

The Ammonites are an extinct group of Cephalopods, which appeared in the Lower Devonian about 400 million years ago and extinguished at the end of the Cretaceous, together with the Dinosaurs (65 million years ago), leaving no known descendants. Like all cephalopods known this organisms were carnivorous: active predators of marine animals, microphagous (plankton), scavengers, and even cannibals. The shell of ammonites in general has the form of a spiral wound on a plan (although some species, such heteromorphy, have a more complex three-dimensional winding) and it is this feature that has given their name. The appearance infact resembles a coiled horn, like that of a ram (the Egyptian god Amon was commonly depicted as a man with ram's horns). Pliny the Elder described the fossils of these animals ammonis cornua, "horns of Ammon." Often the name of the species of Ammonites ends with -ceras, from a greek word (κέρας) whose meaning is, in fact, "horn" (eg. Pleuroceras etymologically means horn with the coast).
The shell was divided by septa into several rooms, including the clam occupied only the last. The others were used as "air chambers" filled with gas and liquid to control the floating body. The ammonite could well change its depth in a manner similar to the current Nautilus.
Because of their extraordinary variability and distribution in marine sediments around the world the ammonites are considered fossils for excellence and guide-fossils of exceptional value, used for dating in stratigraphy of the sedimentary rocks.
The classification of ammonites is made on the basis of morphology and ornamentation of the shell, and the shape of septa, depending on the suture line.