The Archaic Nautilus

Auckland Star, Volume LXXII, Issue 69, 22 March 1941, Page 2 (Supplement)

The Archaic Nautilus

Although the tropica pearly, or chambered, nauti lus does not live in New Zealanc waters, it is well known to mos of us, for its beautifully symmet rical spiral form and striking radiate pattern of red-brown 01 a buff ground make it a hand some mantel ornament to bi found in many homes. Few, how ever, know what an aristocratic shellfish it really is. To-day only throe closely-allied specie are found living and all three are fro l the tropical waters of Melanesia. The represent the sole survivors of an ancien line of octopus-like creatures that one dominated the seae of 300 to 500 millio years ago.

Anyone who has seen a broken nautilus or one that ha* been carefully sliced in two will have marvelled no doubt at the elaborate internal structure of the shell, which is cut tip into compartments by means of beautiful pearly partitions. Each compartment is connected with the next by a small porous tube, the animal always occupying only the large cavity in front, of the outermost partition. Gave Idea for Submarine? The use of these unoccupied partitions has causcd much controversy, but the view generally held is that, they assist t lie animal in li-ing from the ocean depths to the surface, for it is assumed that the compartments can be fully or partially tilled uith gas at will by the animal. Certainly the nautilus is quite adept at varying the depth at which iL .■prefers to feed and the natives of Papua, knowing these habit.3, set baited traps accordingly. Tt is quite possible that the modern Fuhmarine originally developed from knowledge of the chambered structure of the nautilus. and its assumed purpose of

|! By A. W. B. Powell ' d

jt cruising at different levels of the sea. One recalls that Sir Hubert Wilkins named his Arctic-exploring submarine 6 Nautilus, in deference to that ingenious n shellfish. 1- The earliest known fossil forerunner of nautilus was from the archaic Cambrian period of some '>•'>() million years ago. This was a simple chambered IC structure in the form of a long tapered tube. Gradually this creature, which we es term Orthoceras, learned to coil its shell mi so that the resultant spirally-wound py nautilus was a stronger and more comnt pact structure. ce Some, millions of yem-s later a vigoran ous stock broke off from the nautiloius and originated the complex group known

as the ammonites. Externally the ammonite* closely resembled the nautiloids except, that the partitions became elaborately frilled at their junction with the shell. For practirwlly the whole of that great middle period of geological history the ammonites outstripped the nautiloids and became the dominant sea creatures. (Jrefltcr and greater became the complexity of their forms, embodying startling experiments in shape. Some emulating their nautiloid Ancestors became partially uncoiled approaching the shape of the primitive Orthoceras. This seems to have been their undoing, for the close of the great Mesozoie era iaw the last of the ammonites, for they became totally extinct —worn out by the > rapidity and complexity of their vast ■ dc\elopment. Meanwhile, quite unconcernedly, one would gather, the archaic . Nautilus went its own conservative : way, and as a reward its kind breathes to-day. having quietly survived some i .Vin.nno.ooo years. i The ammonites, howe\er, conferred a f great benefit upon the modern geologist, f for they become his time indicators for

the Mesozoic or middle period of geological time. Such rapid development meant that no one form had an extensive distribution in time, and so each of the host of ammonite types becomes an invaluable age index to Mesozoic rocks the world over. Xew Zealand rocks of Mesozoic age are rich in ammonite fossils, and so our geologic formation-; can be correlated with those of the old world. Although nautilus has not survived !o recent times in Xew Zealand it had a fossil ancestor in these waters during 1 lie Tertiary, the third of the great geological divisions, the one r-üb>ei|iient to the Mesozoic and preceding the modern age. -5-