A Fine example of the British fossil Cadoceras sublaeve ammonite, exhibiting intricate suture patterning to the umbilicus. These identify the ammonite and the chamber divisions suggesting the growth cycle of the once living mollusc, part of the cephalopoda group and in this instance are well defined and colourful.
An interesting feature is the associated small Jurassic ammonoid attached by a column of matrix to the much larger cadoceras umbilicus.
The minerals of the fossil bed effecting, through a process of absorption, per-mineralisation. Mineral rich water passes through the tissues of the decaying cephalopod and shell, secreting aragonite rich deposits which harden over a long period of time, producing these wonderful fossil ammonoids and in some instances, forming attractively coloured suture patterning, a blue print of the once extant individual. The sutures were attached to the inner whorl of the shell, the hard chitin exoskeleton.
The complex leafy patterning, the suture lines, are at the point where the septa, the ammonites inner chamber division or wall, meet the inner shell. It is thought these sutures are to give strength to the shell. The suture line being wavy spreads the load around the inner surface of the shell, rather than being a simple curved or linea chamber division, at the point of contact with the inner shell surface. Spreading the load gives the shell more strength over a greater area.
It was first thought the shell needed strength so the ammonites could dive to great depths. However theorists now believe this may not be the case. Ammonites are often found in the fossil record in areas of shallow seas, not great depths. It is now theorised that the shells developed strengthened suture lines to enable the ammonite to grow thinner, lighter and therefore more quickly. Thus retaining strength against predators and damaged, these areas of the shell are called 'point forces' where the ammonite shell has more resistance to attack or predation. Also this rapid growth rate thanks to suture point forces may have possibly enabled the ammonites to evolve to greater sizes, as we see in the fossil record in some Cretaceous ammonoids.
A very good sized specimen with fascinating characteristics. This particular ammonite type is well known for its robust and rounded shaped, commonly referred to as a Cannon Ball ammonite, a popular favourite amongst fossil collectors.