Trilobite Devonian Zoogeography and Provinciality Were

No. 6] Proc. Japan Acad., 5 1 (1975) 447

By Teiichi KOBAYASHI, M. J. A., and Takashi HAMADA University of Tokyo

(Comm. June 3, 1975)

Devonian zoogeography and provinciality were repeatedly discussed in recent years and various opinions were expressed by Erben, Boucot and many others. In Europe and North Africa two magnifacies, that is, the rhenish and hercynian magnifacies are distinguishable in Devonian marine sediments and fossils contained. The former is considered to be connected with the near-shore region and the latter with the off-shore region (Erben, 1962) . Characteristic trilobites of the former are Acaste, Asteropyge, Neometacanthus, Treveropyge and other asteropygids and Homalonotus. These kinds of trilobites are traceable into South Asia as far as Chitral, Pakistan where they made a great endemic development yielding new genera in Bithynia, Turkey and Afghanistan. To define the Europe- Mediterranean province they are more important than the hercynian trilobites many of which are nearly cosmopolitan families and genera. With special reference to brachiopods Boucot, Johnson and Talent (1969) distinguished provinces and subprovinces in the early Devonian palaeogeography as follows : Old World Province Rhenish-Bohemian Subprovince Uralian Subprovince Tasman Subprovince New Zealand Subprovince Cordilleran Subprovince Appalachian Province Malvinokaffric Province Here an attempt is made to pick up some characteristic trilobites which would define such provinces and subprovinces. From the view- point of provinciality most distinctive is the Lower and Middle Devonian fauna of South America and South Africa, namely, the Malvinokaffric fauna which contains many indigenous genera of the Phacopinae, Calmoniinae, Acastavinae and Asteropyginae beside endemic species of the Homalonotidae. This province may extend into Antarctica as well as Ghana, West Africa as suggested by Bur- meisteria (Digonus) antarctica Saul, 1965, in the former and by B. (D.) accraensis Saul, 1967, in the latter. The distribution of Digonus 448 T. KoBAYASHI and T. HAMADA [Vol. 51,

Table I. Devonian trilobite (left) and brachiopod (and trilobite) (right) provinces and subprovinces

is, however, not restricted to the Malvinokaffric province. The occur- rence of Synphoria in the Middle Devonian of the Amazonas basin shows the commingling of the Appalachian member in the Malvino- kaffric fauna, if its generic identification can be warranted (Harrington, 1967; Lesperance, 1975). Recently Ormiston (1972) distinguished four Devonian trilobite areas in North America, namely, Arctic Islands...... Uralian Subprovince Western Canada and Alaska... Siberian-Canadian Old Subprovince World Great Basin...... Cordilleran Province Subprovince Appalachian province where the last extending from Nova Scotia, Canada to Chihuahua, Mexico was separated from the three other subprovinces by land. On the contrary, the early Devonian sea of the Old World province on the Atlantic side has ingressed into this province from the south as far as Oklahoma where a colony of the Bohemian community was discovered. Because the so-called Old world province covers all of the Old No. 6] Devonian Trilobite Provinces 449

and New worlds except for the Malvinokaifric and Appalachian provinces, how to divide this extensive province into subprovinces by its comprehensive fauna is a question. The most conspicuous dis- tinction of the North American faunas from those of Eurasia, Australasia and North Africa is the total absence of Cheirurus except for two imperfect thoracic pleurae procured in Chihuahua and referred to Cheirurus ( ? Crotalocephalus) by Haas (1969) . It is not the less conspicuous that none of the dechenellids is represented in either Australia or New Zealand, if Dechenella (Eudechenella) mackeyi Allan from the latter is excluded (Richters, 1950), notwith- standing the fact that the Dechenellidae are widely distributed in the northern hemisphere. Therefore three areas may be distinguished by means of these characteristic trilobites, namely, Eurasia and North Africa with Crotalocephalina and dechenellids Australasia with Crotalocephalina, but no dechenellids North America with dechenellids, but cheirurids are extremely rare. Now the interprovincial connection is to be discussed. The Devonian fauna of Eastern and Southeastern Asia comprising Cro- talocephalina and dechenellids is intimately related to the fauna of Australasia with regard to the common occurrences of Gravicalymene and indigenous Craspedarges to the western Pacific areas (Talent et al., 1972; Kobayashi and Hamada, 1974). The lack of dechenellids in Australasia may not be an objection against its combination with the part of Asia in a province in view of the fact that the late Middle Devonian trilobites are there not well represented. As pointed out by Maximova (1972), Paciphacops, Odontochile (Kasachstanica and Reussia), Praedechenella and Dechenellurus to- gether with Crassiproetus probably indicate the trans-Pacific route of migration from Kazakhstan to North America through the Mon- golian geosyncline. While no scutelloid is known from the Mongol-Okhotsk geo- synclinal zone, Boreoscutellum occurs in New Siberian Islands and eastern Siberia and Arctopeltis in Novaja Zemlya, the Kuznetsk basin and probably in Ellesmereland. Dechenella is also wide-spread in the Urals, the Soviet Arctic, Siberian platform and North America and various dechenellids were flourished in Canada and Arctic Islands no less than Eurasia. Thus the trans-Pacific faunal connection was maintained through Eastern Siberia and Alaska in the north and through Mongolia in the south. On the basis of salient facts summarized above it is tentatively 450 T. KOBAYASHI and T. HAMADA [Vol. 51, concluded that the following five provinces are distinguishable in the Devonian zoogeography with special reference to the Lower and Mid- dle Devonian trilobites. 1. Europe-Mediterranean Province extending easterly as far as Pakistan. 2. Arcto-Pacific Province comprising the Siberian-Canadian Sub- province in the north and the Kazakhstan-Mongolian-Okhotsk Subprovince in the south. On the eastern Pacific side this province extends southerly into the Cordilleran Subprovince from Canada and Alaska. 3. Western Pacific Province composed of the Oriental Subprovince in the north and the Tasman-New Zealand Subprovince in the south. 4. Appalachian Province which may be subdivided into the Appala- chian mountains Subprovince and the Central lowland Subpro- vince. 5. Malvinokaffric Province. The provinciality of Devonian trilobites will be discussed in a further detail in near future. This is an advance report in a project of research on Japanese trilobites now in progress with a grant in aid of the Japan Academy.

References

Boucot, A. J., Johnson, J. G., and Talent, J. A. (1969) : Early Devonian brachiopod zoogeography. Sp. Pap. Geol. Soc. Amer., 11'9, 113 pp. Douma.ni, G. A., Saul, J. M. et al. (1965) : Lower Devonian fauna of the Horlick formation, Ohio range, Antarctica. T. B. Hadley (ed.) Geol. and Paleont. of Antarctica. Antarct. Res. Ser., 6, p. 241-274. Erben, H. K. (1962) : Zur Analyse and Interpretation der rhenischen and her- zynischen Magnifazies des Devons. 2 Intern. Arbeitstagung uber die Silur/ Devon-Grenze and die Stratigraphie von Silur and Devon. Bonn-Bruxelle, 1960. Symposium-Band. S. 42-61. Haas, W. (1969) : Lower Devonian trilobites from central Nevada and northern Mexico. Jour. Paleont., 43, p. 641-659. Harrington, H. J. (1967) : Devonian of South America. Intern. Symp. on the Devonian System, Calgary, 1967, 1, p. 651-671. Kobayashi, T., and Hamada, T. (1974) : On the geological age of the Fukuji formation in the Hida plateau. Proc. Japan Acad., 50, p. 760-763. Lesperance, P. L. (1975) : Stratigraphy and paleontology of the Synphoriidae (Lower and Middle Devonian Dalmanitacean trilobites). Jour. Paleont., 40, p. 91-137. Maximova, Z. A. (1972) : New Devonian trilobites of the supe.rfamily Pha- copidea. Paleont. Jour. 1972, no. 1, p. 88-94. Ormiston, A. R. (1972) : Lower and Middle Devonian trilobite Zoogeography in northern North America. Intern. Geol. Congr. XXIV Sess. Canada, 1972, Sec. 7, Paleontology, p. 594-604. No. 6] Devonian Trilobite Provinces 451

Richter, R. and E. (1950) : Arten der Dechenellinae (Tril.). Senckenbergiana, 31, S. 151-184. Saul, J. M. (1967) : Burmeisteria (Digonus) accraensis, a new homalonotid trilobite from Devonian of Ghana. Jour. Paleont., 41, p. 1126-1136. Talent, J. A, et al. (1972) : Provincialism and Australian early Devonian faunas. Jour. Geol. Soc. Australia, 19, p. 81-97.