Late Olenekian Radiolarians from Bedded Chert of Ashio Terrane, Northeast Japan, and Faunal Turnovers in Western Panthalassa during Early Triassic

Late Olenekian assemblages in the western Panthalassa have been recovered from bedded radiolarian chert sequences of an accretionary complex, the Ashio belt. These faunas are documented and considered in terms of radiolarian diversity and faunal turnover during the latest Permian to Middle Triassic time. The fauna includes 30 radiolarians belonging to Spumellaria or Entactinaria, with two relicts from the Late Permian. This late Olenekian fauna is markedly different from Permian and Anisian faunas, respectively, and is herein named the Minowa fauna. Study of the literature indicates that radiolarian provinces were significantly disconnected between the western Panthalassa and eastern Tethys during late Olenekian time. Furthermore, 121 of 143 species disappeared during late Olenekian time, and in turn 118 new species appeared in the western Panthalassa around the Olenekian Anisian boundary. It is concluded that faunal turnover occurred at least three times between the latest Permian and Middle Triassic. The first turnover is the Paleozoic type radiolarian extinction at the Permian Triassic boundary, the second is the diversification of spheroidal Spumellaria and Entactinaria between early and late Olenekian time, and the third is a faunal turnover from the Minowa fauna to the true Mesozoic type radiolarian faunas that are characterized by multi segmented Nassellaria.

Biochronology,paleobiogeography and faunal turnover in western Mediterranean Cenozoic mammals

Cenozoic terrestrial mammals from Sardinia contribute substantial information for reconstructing the complex his-tory of the western Mediterranean.The occurrence of endemic perissodactyls in Eocene marine and marsh deposits suggests the existence of ecological or physical barriers between the Corso-Sardinian massif and the Iberian-Occitanic area.At the end of the Oligocene,isolation of Sardinia was almost complete,although a migration from Europe occurred at the beginning of the Early Miocene,as indicated by the unbalanced endemic fauna from Oschiri.During the Late Miocene,the Tusco-Sardinian palaeobioprovince came into existence as an isolated region inhab-ited by the quite diversified,but notably endemic,Oreopithecus fauna.Sardinia was definitely isolated from Tuscany by the Messinian,but temporary connections with the European mainland possibly allowed the colonization of forerunners of some Sardinian Pliocene taxa.During the Plio-Pleistocene,Sardinia maintained permanent isolation.However,sea level drop,resulting in a relatively short distance between Sardinia and the European mainland,allowed different migratory events.From the Late Pliocene to the Late Pleistocene–Holocene,two main mammalian faunal complexes(FC)can be recognized:the Nesogoral FC(Late Pliocene-Early Pleistocene)and the Microtus(Tyrrhenicola)FC(late Early Pleistocene–Early Holocene).At the transition from Nesogoral to Microtus(Tyrrhenicola)FC,approximately 47%of the genera and 76%of the species disappeared,while approximately 58%of the genera and 71%of the species appeared.A noticeable turnover followed the arrival of Neolithic man and his accompanying fauna.Nonetheless,Praemegaceros was still present at about 7000 years BP,while Microtus(Tyrrhenicola)and Prolagus are respectively recorded in the Bronze and Iron Ages.