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

The detailed morphological description of the skull of the stem turtle <i>Heckerochelys romani</i> from the Middle Jurassic (Bathonian) of the Peski locality, Moscow Region, Russia, is provided herein. All cranial structures of <i>Heckerochelys romani</i> 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 <i>Heckerochelys romani</i> and <i>Eileanchelys waldmani</i>, except for the size. Several cranial characters of <i>Heckerochelys romani</i>, 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.