82. Comparison O F Ordovician Cephalopods Between Australia

No. 9] Proc. Japan Acad., 63, Ser. B (1987) 313

82. Comparison of Ordovician Cephalopods between Australia and Eastern Asia

By Teiichi KoBAYASHi, M. J. A.

(Communicated Nov. 12, 1987)

In Australia the oldest cephalopods are ellesmeroceroids in the Ninmaroo limestone of Black Mountains, West Queensland which have been reported by Whitehouse (1936) soon after the publication of the Wanwanian ellesmeroceroids from South Manchuria (1933) . The Toko series which overlies the Ninmaroo limestone contains Actinoceras, Calhounoceras and some new genera resembling Kochoceras and Armenoceras. These Wanwanian and Toufangian cephalopods appear, however, still remain undescribed. The Larapintine series in the McDonnell Range and Finke River regions, Central Australia yields a copious Ordovician fauna including many species of Orthoceras, Endoceras, Actinoceras and Trocholites. Because this fauna, is inti- mately related to the Chikunsan fauna followed by the Tsuibon and Touf angian faunas among the Ordovician ones in Eastern Asia, I suggested Llandeilian, s. 1. for its age (1940). One year before this, Bathomoceras australe Teichert, 1939 was described therefrom and its age was considered latest Arenigian to early Llanvirnian. However, Armenoceras and some younger genera were later found from Ellery Creek (Teichert, 1952) . Therefore the Larapintine series may be pene-contemporaneous to the Toufangian series inclusive of the Maruyaman stage. The Emanuel limestone in the Kimberley region, Western Australia is rich in cephalopods, particularly in its middle portion and its age is middle to late Canadian, although the upper part containing Meniscoceras may be as high as Chazyan (Flower, 1941). Hardomanoceras lobatum is obtained from the main cephalopod limestone. Hardomanoceras is known now to be an important key to the Wolungian age on the western Pacific side, as this genus is widely distributed from Jilin, South Manchuria to Australia through Tarutao Island on the Thailand-Malaysia border (1959). In New South Wales there are two assemblages of late Ordovician cephalopods allied to the Asiatic ones. The older one in Fossil Hill limestone contains Troedssonella which may be Llandeilian-early Caradocian in age and shows affinities to the faunas of China, Kazakhstan, Central Siberia and Sweden. The younger or Ashgillian fauna comprises Troedssonella and Paradiscoceras the latter of which is known from Kazakhstan and northeastern USSR. Broadly speaking, the Middle Ordovician cephalopods occur in Central Australia and later Ordovician ones in Southeastern Australia, while the older Ordovician genera are known from Western Australian and Western Queensland. Beside the Piloceras-Manchuroceras assemblage discussed in the preceding article five other assemblages are distinguished in Tasmania (Stait, 1984) as follows : 1. Wutinoceras-Adamsoceras assemblage In Tasmania Wutinoceras is represented by Nybyoceras multicubiculatum Teichert and Glenister and N. paucicubiculatum Teichert and Glenister (1975). This assemblage is related to the Maruyaman fauna of Eastern Asia through 314 T. KOBAYASHI [Vol. 63(B),

Wutinoceras sp. 2. Discoceras-Gorbyoceras assemblage Discoceras reveals affinities to the cephalopods of the Pagoda limestone in Central China. 3. Tasmanoceras-Hecatoceras-Gouldoceras assemblage 4. Gordonoceras assemblage 5. West ieldceras assemblage The above three assemblages (3-5) characterized by indigenous genera show so high endemism that Tasmania was quite isolated at that time from the Asian and other faunas. Incidentally Trocholithoceras idaense Teichert and Glenister, 1953 was once located in Trocholites by Flower (1962), but now it is placed in Discoceras by Stait (1983). Gorbyoceras settlemense Stait and Flower, 1985 from Ida Bay looks similar to To f angoceras and also To f angocerina. In Tasmania Wolungian cephalopods are the oldest members. The Toufangian and later ones are well developed in Tasmania. Although the occurrence of Piloceras in Tasmania means a contact with the faunas of Americas temporarily in the late Canadian age, the Australian cephalopods maintained intimate re- lationship with the Asiatic ones during the Ordovician period. Judging from Hardmanoceras, Manchuroceras and Wutinoceras the Burmese-Malaysian geo- syncline (1977) must have been the main route of migration. There the actinoceroid-bearing limestone is traceable from near Kuala Lumpur to North- west Thailand (Kobayashi, Gan, and Murthy, 1979) and further to the north into the so-called "Orthoceras bed" in the Ordovician Formation of the Shan Plateau, Burma. Irianoceras antiquum was found on the Irian side near her frontier to Papua (Kobayashi and Burton, 1971), but little is as yet known of Ordovician cephalopods in the 3 N Arc comprising New Guinea, New Caledonian and New Zealand.

References`'

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