Cranial morphology of Heckerochelys romani Sukhanov, 2006, a stem turtle from the Middle Jurassic of European Russia, with implications for the paleoecology of stem turtles

ABSTRACT

The detailed morphological description of the skull of the stem turtle Heckerochelys romani from the Middle Jurassic (Bathonian) of the Peski locality, Moscow Region, Russia, is provided herein. All cranial structures of Heckerochelys romani prove to be more advanced than in the Triassic and Early Jurassic stem turtles, but more primitive than in crown turtles; its morphology can be basic for both Cryptodira and Pleurodira. Only a few insignificant differences in skull morphology could be found between Heckerochelys romani and Eileanchelys waldmani, except for the size. Several cranial characters of Heckerochelys romani, such as architecture of the feeding apparatus and geometry of the cavum tympani, may indicate the aquatic habitat preference for this turtle, which is supported by taphonomic conditions.

ACKNOWLEDGMENTS

We thank N. V. Gordenko and A. G. Sennikov for advice on geology of the Peski locality, A. G. Sennikov for the pictures of the Peski locality; S. D. Shvets, K. Yu. Iltsevitch, and A. I. Osochnikova for assistance in preparing the figures. The editor T. Lyson, the reviewers S. Evers and W. Joyce are thanked for their profound reviews and useful comments. A. Ostroshabov is thanked for the painting of Heckerochelys romani in the paleoenvironment. The study was supported by the Russian Foundation for Basic Research grant No. 20-04-00222A; and the Zoological Institute, Russian Academy of Sciences (project 122031100282-2).

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

AUTHOR CONTRIBUTIONS

EMO: investigation; methodology; photographs; drawings; description; writing the original draft; reviewing and editing. VBS: investigation; material curation; photographs. IGD: investigation; methodology; project administration; resources; supervision; reviewing and editing.

SUPPLEMENTARY FILES

Supplementary File 1.doc: Figures S1–S21. Photographs and drawings of isolated skull bones of Heckerochelys romani in high resolution.

Supplementary File 2.doc: Figures S22–S31. Photographs of the articulated blocks of skull bones of Heckerochelys romani in high resolution.