MSU paleontologists reported the discovery of the oldest bivalve mollusk of the genus Pinna. The find comes from the deposits of the Early Permian reef of Shakhtau on the territory of Bashkiria. Information about the discovery was published in the Paleontological Journal.

The Pinnidae Leach family includes some of the largest heteromiare bivalves. The first representatives of this family appeared in the early Carboniferous. In ancient times, an expensive cloth – visson was made from the bisexual threads of these mollusks. Clothing made of this material was highly valued because of its durability.

Currently, pinnids are widely distributed in tropical and subtropical seas and are of great commercial importance. To date, these are some of the most recognizable double doors. But despite all this, the evolutionary history of the family raised a number of questions. First of all, the connection between the Paleozoic stage of development of the family, none of whose representatives survived the Permian-Triassic extinction, and the Meso-Cenozoic stage, which is characterized by modern-type pinnids, in particular, the well-known genus Pinna, was unclear.

The oldest representative of this genus to date has been known from the Lower Triassic of Japan. Thus, a gap not characterized by the findings of pinnids was revealed in the fossil record.

"During field work on the sediments of the Assel-Sakmar reef of Shakhtau (Bashkortostan), the oldest representatives of the genus Pinna were found, which belong to a new species – P. pacata (from Latin pacatus – peaceful). The described species changes the idea of pinnas as exclusively Meso-Cenozoic forms, and also increases the stratigraphic interval of the genus distribution by 42 million years," said Lev Shilekhin, one of the authors of the article, a student of the Department of Paleontology of the Geological Faculty of Moscow State University.

In 2022-2023, research began on perhaps the most diverse complex of Early Permian bivalves in the world, which was collected in Shakhtau during the expedition work of the A.A. Borisyak Paleontological Institute of the Russian Academy of Sciences. The study of the fossil bivalves of Shakhtau confirms that the Ural Strait in the Assel-Sakmar period was one of the centers of diversification of the Early Permian mollusk fauna, which was previously shown on cephalopods and gastropods.

The study was attended by Lev Shilekhin, a student of Lomonosov Moscow State University, Alexey Mazaev, a leading researcher at the A.A. Borisyak Paleontological Institute of the Russian Academy of Sciences, and Alexander Byakov, Chief Researcher at the N.A. Shilo Northeastern Integrated Research Institute of the Far Eastern Branch of the Russian Academy of Sciences.

The work was supported by the Russian Science Foundation (grant No. 22-24-00099 "Evolution of molluscan communities of the Early Permian reef of Shakhtau").

Information provided by the MSU press service

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