GENERAL GEOLOGY

Detailed explanation-1: -The essential difference between the nautiloid and ammonoid shell is in the partitions that separate the chambers; the nautiloid partitions are undulating and of “free-form” appearance, whereas those of the ammonoid are much more highly crenulated and therefore more complex.

Detailed explanation-2: -A primary difference between ammonites and nautiloids is the siphuncle of ammonites (excepting Clymeniina) runs along the ventral periphery of the septa and camerae (i.e., the inner surface of the outer axis of the shell), while the siphuncle of nautiloids runs more or less through the center of the septa and camerae.

Detailed explanation-3: -The sutures of Nautiloids tend to be more regular and simple (straight like orthocone Nautiloid cephalopods) or gently curved. Modern Nautilus only shows the curvature of septa. Ammonoids, however, tend to have complex sutures with crenulations.

Detailed explanation-4: -Ammonite is an extinct mollusc, while nautilus is an extant mollusc. The siphuncle ran around its shell’s outer edge through the edge of every septum in ammonites. In contrast, the siphuncle runs through the center of the shell in nautilus. The septa are simple in nautilus, while the septa are complex in ammonites.

Detailed explanation-5: -The suture line of nautiloids is straight, but it is folded in other kinds of shelled cephalopods. Modern nautiloid cephalopod shells are coiled, but extinct forms may also be straight or curved.