New fossils of Sinomegaceros ordosianus (Cervidae, Mammalia) from the Yitong River basin, northeastern China

Sinomegaceros ordosianus is an endemic giant deer that primarily wandered in northern China during the Late Pleistocene. Here, we describe new specimens of S. ordosianus unearthed from the Yitong River basin, Jilin Province, northeastern China. The antler beams exhibit pronounced ontogenetic changes, becoming more curved and robust in adult individuals. We interpret that these changes enhance its load-bearing capacity to support the greater weight of the terminal palmation. The described partial skull provides valuable information regarding the skull and labyrinth morphology for the first time, e.g. it reveals a thickened bone wall, a trait shared with other giant deer species, and the bony labyrinths of S. ordosianus and Megaloceros giganteus are similar in a few features, including the vestibular aqueduct, endolymphatic sac, and the insertion position of the lateral semicircular canal into the vestibule. The mandible of S. ordosianus is less robust than that of Sinomegaceros pachyosteus and Sinomegaceros flabellatus. A direct radiocarbon date on a tooth from the mandible yielded an age of 34990 ± 300 BP. The fossil records and distribution suggest that the lower reaches of the Yangtze River may be one of the potential refugia for S. ordosianus during the Last Glacial Maximum.