A new cranium of Metacervocerus longdanensis (Cervidae, Mammalia) and the genus Metacervocerus in China

This study documents a skull of the large cervid Nipponicervus longdanensis from the Early Pleistocene (~2.6-2.1 Ma) of Longdan, Gansu, China. Morphological comparisons indicate that N. longdanensis exhibits the type of “adaptive” distal fork (anterior tine smaller and oriented along the beam) that differs from the type species Nipponicervus praenipponicus, while it is aligned with Metacervocerus Dietrich, 1938, necessitating reclassification as Metacervocerus longdanensis. The cranium exhibits posteriorly inclined pedicles demonstrating phylogenetic affinity with M. elegans (Nihewan Basin) and M. rhenanus (Europe), while derived features including a shortened neurocranium, rostrally tapered basioccipital, and duplicated P4 protocone distinguish it as an advanced lineage within the genus. Character assessments reveal that Metacervocerus is potentially paraphyletic because Metacervocerus? shansius and Metacervocerus? punjabiensis retain plesiomorphic conditions (elongated braincase, simple P4 morphology), while they exhibit pronouncedly erected pedicles and lyrated antler beams, suggesting a divergent lineage from Metacervocerus longdanensis. Previously published isotopic data (δ13C = −10.9‰ ± 0.9‰, δ18O = −7.5‰ ± 0.9‰, n = 4) indicate a semi-open habitat and a browsing-to-mixed feeding ecology of M. longdanensis. This revision resolves persistent taxonomic uncertainties in Eurasian Cervinae while elucidating East Asia’s biogeographic significance in driving cervid morphological radiation during the Plio-Pleistocene transition.