New data on the Miocene vertebrate assemblage of the Zaysan Basin (Central Asia) with implications for biostratigraphy, paleoecology, and paleobiogeography

ABSTRACT

The Zaysan Basin in Central Asia has a long geological history, and it has therefore seen major climatic and evolutionary transformations. The Miocene fossil record of this locality is remarkably rich representing all groups of vertebrates. A revision of fish remains has been carried out and new records of fishes, reptiles, and mammals recovered from Miocene deposits of the Zaysan Basin have been described. The study of fossils has revealed the existence of a quite diverse vertebrate assemblage in the basin during the Miocene. Representatives of the Percidae and Amiinae, and the species †Leobergia zaissanica predominated among fishes, whereas reptiles were supposedly represented in the assemblage by pan-trionychid turtles and crocodiles. No amphibians have been revealed, while the only mammalian taxa in the studied sample is a fossorial rodent of the genus †Tachyoryctoides. In contrast to previous views regarding the Middle Miocene age of the Zaysan Formation, the analysis of fish and mammal remains recovered from this locality strongly suggests an Early Miocene age. Findings of bowfin remains in the Zaysan Basin confirm that this group had existed outside of North America beyond the Paleogene/Neogene transition, and, at the same time, these specimens are the last known occurrences of the taxa Amiidae, Amiiformes, and Halecomorphi outside of North America. Data also indicate the existence of a lacustrine ecosystem in the Zaysan Basin during the Miocene with a taxonomically rich vertebrate assemblage and diverse trophic relations being an important center of biodiversity in the Miocene of Central Asia.

ACKNOWLEDGMENTS

The research of O. Kovalchuk and Z. Barkaszi was carried out in the frames of the project ‘Reconstruction of Cenozoic marine ecosystems within the Central and Eastern Paratethys’ supported by a grant from the National Academy of Sciences of Ukraine (No. 0121U110402). We are thankful to I. Danilov (Zoological Institute of the Russian Academy of Sciences, Saint Petersburg) and Y. Kimura (National Museum of Nature and Science, Japan) for their constructive review of the manuscript. The editors J. Kriwet, A. López-Arbarello, and J. Harris are acknowledged for their effective management of our submission. The authors express their thanks to the late E. Sytchevskaya (Borissiak Palaeontological Institute, Moscow, Russia) for the inspiring discussion on Miocene teleost fishes of the Zaysan Basin. We are thankful to M. Chmielewski (Wrocław University, Wrocław, Poland) for preparing of SEM photos of cyprinid remains, as well as to L. Rekovets (Wrocław University of Environmental and Life Sciences, Wrocław, Poland), P. Raczyński and K. Lipiec-Sidor (Wrocław University, Wrocław, Poland) for their kind help during the preparation of the manuscript. We further wish to thank M. Delfino (Università degli Studi di Torino, Turin, Italy) for the discussion of reptile fossils from Central Asia.