Fossil Ammonite - 4.5 cm - Sahara Desert - NEW

They had a thin shell of aragonite, planispiralada and with a very marked ornamentation, consisting of well-defined ribs. Said shell is divided into two zones: the "phragmocone", which is the partitioned part of the shell where the gases that control the buoyancy of the animal are stored; and the "inner chamber", which is where the soft parts were housed.
Inside the "phragmocone" are the "septa", which partition this part of the shell, with their concavity directed towards the anterior region. Ammonites were thus opisthocoelic organisms. The septa have a hole, called "siphonal neck", oriented towards the posterior region that allows communication with the rest of the septa through the siphon. The intersection of the septa with the external wall of the phragmoconus draws in it the so-called "suture".
There are several types of sutures:
Orthoceratitic: simple, with a small inflection
Goniatitic: with more marked and rounded inflections.
Agoniatitic: the inflections are pointed.
Ceratitic: alternately crenulated and horseshoe-shaped inflections.
Ammonitic: the inflections are very cut and with multiple subdivisions.


Section of an ammonoid showing the chambers with different sedimentary fillings and mineral growths.
The direct advantage of the complication of the suture is related to the increased resistance of the shell. The more contact there is between the tabique and the wall of the phragmocone, the more resistant it will be.
This advantage was not taken advantage of by the ammonoids to be able to descend to greater depths, but was accompanied by a decrease in the thickness of the shell, thus losing weight but not resistance and gaining swimming effectiveness. The fact that species that could go down to greater depths did not appear is related to the internal pressure of the siphon, since it was lower than that of the fluid from the outside, so this siphon would explode if they went deeper.
Po define the morphology of the shell we must look at the section of the spiral, which can be lanceolate, semicircular or circular, and the degree of embracing of the spiers, which can be oxycone, serpenticon or platicone.

Measurements: 4.5 cm.