They had a thin shell of aragonite, planiespiralada and with a very marked ornaments, consisting of well-defined ribs. The shell is divided into two zones: the "fragmocono", which is the branching part of the concha where are stored the gases that control the buoyancy of the animal; and the "inner Chamber", which is where the soft parts were staying.
The "fragmocono" inside inside "SEPTA", who tabican this part of the shell, its concavity directed toward the anterior region. The ammonites were thus opistocelicos organisms. SEPTA have a hole, called "neck siphon", oriented towards the posterior region that allows communication with the rest of SEPTA through the siphon. The intersection of SEPTA with the outer wall of the fragmocono draws on it called "suture".
There are several types of sutures:
Ortoceratitica: simple, with a small breakthrough
Goniatitica: with inflections more marked and rounded.
Agoniatitica: the inflections are sharp.
Ceratitica: inflections with horseshoe-shaped and crenuladas Alternatively.
Amonitica: the inflections are very clipped and with multiple subdivisions.
Section of an ammonoideo showing the Chambers with different sedimentary fills and growthmineral s.
The direct benefit of the complication of the suture is related to the increase in resistance of the shell. How much more contact there is between the wall and the wall of the fragmocono, more resistant will be this.
This advantage was not used by the ammonoideos to be able to descend to greater depths, but wine accompanied by a decrease in the thickness of the shell, thus losing weight but not resistance and winning swim effectiveness. Which appeared not species which could drop to greater depths is related to the internal pressure of the trap, since it was less than the fluid from the outside, so this trap would explode if they deepen.
To define the morphology of the shell we must look in the section of the spiral, which may be lanceolate, semi-circular or circular, and in the degree of embracing of the loops, which can be oxicono, serpenticono or platicono.
Dimensions: 4.5 cm.