Ancient Species

Nautiloids

Nautiloids are molluscs with shells resembling the modern nautilus. The shell is divided into chambers by partitions called septa. The body of the animal is in the last, and largest, of the chamber. A fleshy stalk, the siphuncle,  extends backward through the septs.

The first nautiloids appeared in the early Cambrian Period (570 million years ago). These were tiny creatures with straight, cone-shaped shells less than a quarter of an inch long. Their descendants grew large4r and longer until the middle of the Ordovician Period (525 to 43 million years ago) when some reached 12 feet in length.

Curved shells appeared towards the end of the Cambrian Period (505 million years ago). Some evolved shells which began to curve tightly and then straightened out. The coils helped keep the animal upright and, unlike straight shells, did not get in the way when they swam. As a result coiled nautiloids survived much longer than straight ones.