Adjustable Bronze Ring with Ammonite -11-
Adjustable Bronze Ring with Ammonite -11-
Approximate part size: 2.5x2cm
Approximate weight: 9gr
The parts to be delivered are similar to those in the photographs
Ammonoids are thought to have very fine shell and organic composition. For this reason its conservation has proved difficult, so most ammonites are in the form of a mold, having disappeared the shell by diagenesis. On the other hand that allows us to see in great detail the growth of its cameras, which is reflected on the outside creating a drawing with the appearance of sheets.
On the other hand, this piece has been sectioned in half, and we can perfectly observe the interior chambers. It is composed of two types of minerals; calcite and aragonite. It's very difficult to distinguish from each other with the naked eye. It is not a law but there is a small trick to differentiate them, and is that the aragonite often under ultraviolet light reacts phosphorescently.
Cephalopods owe the name to their most notable feature, which is the possession of a variable number of arms or tentacles around the head (8 in Octopus, 10 in Loligo, 90 in Nautilus).
These are the most specialized molluscs and the highest organization. It is worth noting its eyes, comparable in their complexity to those of vertebrates. Despite having more than 600 species today, it must be considered a decaying species, taking into account that there are more than 10,000 species in its fossil record. Cephalopods appeared during the cambrian and were of the utmost importance during paleozoic and mesozoic. In the fossil record stand out the orthoceras, ammonites and belemnites as more characteristic representatives.
They are exclusively marine animals most nectonic and some are benthic. They are displaced by expulsion of water and/or gases contained in the paleal cavity. All current cephalopods are carnivores, feeding on crustaceans, gasteropods and other organisms that trap with their tentacles and devour with the help of their parrot-billed jaws.
Some cephalopods have an outer shell (nautilus), others internal (sepia), while others lack it (octopus). Argonaut secretes a shell to incubate eggs during reproduction. As a morphological element of cephalopods, the shell has a dual function: to protect the soft parts and hydrostatic apparatus for flotation, balance and movement within the water.
Cephalopods have separate sexes and in some cases exhibit a marked sexual dimorphism.
Representatives of this class are known by the common name ammonites or ammonoids. About 2000 genera of ammonoids have been reported.
The ammonoid shell, with a few exceptions, has a compact planiapiral shape. Some primitive genera, however, have a central hollow (like certain male-rolled paleozoic nautiloids). The shell can be involute or evolute and its general shape, flattened, compressed, globular, subspheroidal, etc. Its maximum dimensions range from 1cm to 3m.
In most specimens the siphon has been in the ventral position or in some cases more scarce in dorsal position. The dorsal necks are usually retrocoaned, although there are also procoanados. These seconds belong to the most evolved forms.
Unlike nautiloids, ammonoids often have ornamentations in the shell. This ornamentation consists of more or less marked growth lines, ribs with or without tubers and spines, keel or keels in the ventral area, and sometimes ears located on both sides of the opening.
Ornamentation is important in the systematics of ammonoids, but because of the group's tendency to homeomorphia, other characteristics, for example sutures, must be taken into account. In fact the suture of ammonoids is the most commonly used character for the classification of paleozoic forms. In Mesozoic forms, the configuration of laps, ornamentation and type of winding are also considered among other characteristics.
The sexual dimorphism of the ammonites could become important, with shells 2 to 4 times larger than each other, different openings and different separations between room chamber and the rest of the shell. It is not clear in each case that morphology belonged to the male and which to the female.
Associated with ammonoids, there was often a limestone plaque that at first glance looked like bivalve: they are the so-called aptic. Because of their shape and position they have been interpreted as operculums protecting the animal's body when retracted into the shell. Other less important structures of chitinous or organic composition, sometimes associated with ammonoids, are so-called anaptic, formed by flat butterfly-shaped plates that have been interpreted as mandybular pieces similar to those of coleoids.
How do we differentiate an ammomonite from a nautilus?
Other than the most pronounced ornamentation of the ammonoids, in general a finer shell than the nautiloids. It is also said that the symphonal necks are procoanated in the ammonoids and retrocoated in the nautiloids, that the symphon of the ammonites is in a ventral position and that their septos are usually convex towards the opening, however they are generalities that are not always met.