New Find of Inoceramus -Like Bivalves of the Genus Atomodesma in the Southern Verkhoyansk Region, and Invasions of Extra
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Find of Inoceramus-Like Bivalves of the Genus Atomodesma in the Southern Verkhoyansk Region, and Invasions of Extra-Boreal Mollusks into Northeastern Asia during the Permian A. S. Biakova, b, * and R. V. Kutyginc aNorth-East
Interdisciplinary Scientific Research Institute n. a. N.A. Shilo, Far East Branch, Russian Academy of Sciences, Magadan, 685000 Russia b Kazan (Volga Region) Federal University, Kazan, Republic of Tatarstan, 420008 Russia cDiamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Sciences, Yakutsk, 677000 Russia *e-mail: [email protected] Received November 11, 2019; revised November 22, 2019; accepted November 24, 2019
Abstract—Inoceramus-like bivalves of the bipolar species Atomodesma variabile Wanner were first found and precisely associated with the Upper Permian (Wuchiapingian) section in the Southern Verkhoyansk Region. The appearance of this exotic taxon in Boreal basins is associated with the short-term invasion of several Tethyan taxa into high-Boreal basins due to transgression. It is concluded that the similarity of the Permian marine biota from the Boreal and Notal (Gondwanan) paleobiogeographic superrealms is largely due to periodic invasions of notal elements into Boreal basins. The species A. variabile is described and illustrated. Keywords: Inoceramus-like bivalves, invasions of extra-Boreal mollusks, Permian, Southern Verkhoyansk Region, Northeast Asia DOI: 10.1134/S0031030120050032
INTRODUCTION Inoceramus-like bivalves were a striking element of benthic assemblages of northeastern Asia during the Permian (Biakov, 2008, 2010). They are especially typical of the Verkhoyansk Basin, where they form thick coquina interbeds, composed mainly of representatives of the genera Aphanaia and Kolymia (Middle Permian) and those of the genera Maitaia and Intomodesma (Upper Permian). Almost all of them belong to high-boreal endemic taxa. There are also finds of Inoceramus-like bivalves, belonging mainly to genera Atomodesma, Aphanaia, and Maitaia, although not so numerous, in the Notal (Gondwanan) paleobiogeographic Superrealm (mainly, in basins of Australia and New Zealand) (Dickins, 1956, 1963; Waterhouse, 1959, 1979; etc.). Thus, this group is characterized by bipolar distribution and this phenomenon is still poorly understood. Species of the genus Atomodesma Beyrich sensu stricto were first described from the Notal Paleobiogeographic Superrealm (Beirich, 1864), where they were represented by a few species since at least the Early Permian (Waterhouse, 2008). Note that this characteristic taxon is still considered by some experts, especially, in the field of Triassic bivalves (Foster et al., 2019; Hautmann et al., 2015), in its original broad sense, which we consider incorrect. Moreover, the occurrence of Boreal–Notal taxa in typical Tethyan warm-water assemblages (South
China, in particular) seems very controversial, especially given the poor preservation of the material from South China. It is not clear whether these forms generally belong to Inoceramus-like bivalve
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