Xinjiangchelyid turtles from the Middle Jurassic of the Berezovsk coal mine (Krasnoyarsk Territory, Russia): systematics, skeletal morphology, variation, relationships and palaeobiogeographic implications

Abstract

This paper is devoted to the description of a new species of xinjiangchelyid turtle – Annemys variabilis sp. nov. – represented by thousands of isolated bones and several more complete specimens from the Middle Jurassic (Bathonian) Itat Formation of the Berezovsk coal mine, Krasnoyarsk Territory, western Siberia, Russia. The description is based on a sample of the best-preserved specimens. The new species differs from other Annemys spp. by a combination of cranial and shell characters. The basisphenoids (about 200 specimens) of A. variabilis demonstrate variation in 12 characters, some of which are reported in turtles for the first time. About 20 shell characters of A. variabilis are subject to ontogenetic or interindividual variation. Some of these characters are variable in other Annemys spp. and other xinjiangchelyids. The formula of the cervical vertebrae [(2(3()4()5()6()7()8) or (2(3()4()5()6()7()8(] with two opisthocoelous vertebrae (2 and 3), four or five amphicoelous vertebrae (4–7 or 4–8), and one procoelous vertebra is unique for this species among xinjiangchelyids, which were previously known to have only amphicoelous cervicals. Other characters of the non-shell postcranium correspond to those of other xinjiangchelyids. Of the three phylogenetic analyses performed in this study, Analysis 1 does not support the monophyly of either Xinjiangchelyidae or Annemys, Analysis 2 shows paraphyly of Xinjiangchelyidae and monophyly of the Annemys clade (A. latiens, A. levensis, A. variabilis and A. wusu), and Analysis 3 supports monophyly of the Annemys clade with A. latiens, A. levensis and A. variabilis, only in the majority rule consensus tree. The diversity of the turtle assemblage of the Itat Formation is re-assessed as containing 2–3 taxa (A. variabilis [=Testudines indet. 2], Testudines indet. 1 and 3), which is in agreement with similar diversities seen in some other Middle Jurassic Asian turtle assemblages. The known record of Annemys spp. is restricted to the northern part of Asia.

https://zoobank.org/urn:lsid:zoobank.org:pub:E836F02F-21DD-4A36-ACBB-4170A6CD46AD

Keywords:

• Testudines
• Xinjiangchelyidae
• Middle Jurassic
• Asia
• Siberia

Acknowledgements

The authors are grateful to all who participated in the collection of material in the Berezovsk coal mine (see Averianov et al. 2016) and to A. A. Ostroshabov (Zoological Institute of the Russian Academy of Sciences, St. Petersburg, Russia) for the painting of the hypothetical reconstruction of Annemys variabilis. Two reviewers (W. G. Joyce and an anonymous reviewer) are thanked for useful comments and corrections to the English. This study was supported by the Russian Science Foundation (19-14-00020-G; work of EMO and IGD on shell and non-shell postcranial material), Russian Foundation for Basic Research (project No. 20-04-00222A; work of IGD, EMO and VBS on skull material) and the Zoological Institute, Russian Academy of Sciences (project 122031100282-2).

Supplemental material

Supplemental material for this article can be accessed here: http://dx.doi.org/10.1080/14772019.2022.2093662.

Associate editor: Richard Butler