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 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.

报道了产自甘肃龙担早更新世(约2.60–2.1 Ma)的一件鹿科头骨标本。其保存的角形态特征与龙担日本鹿(Nipponicervus longdanensis)相符。分类修订确认龙担日本鹿具有“适应型”的鹿角(远端分枝中前枝小于后枝且延伸方向与主枝相同), 与“非适应型”的日本鹿属型种前日本鹿(Nipponicervus praenipponicus)不同，而与后枝角鹿(Metacervocerus Dietrich, 1938)属相同，故将其重新命名为龙担后枝角鹿(Metacervocerus longdanensis)。该头骨具有后倾的角柄，显示其与泥河湾盆地的秀丽后枝角鹿(M. elegans)及欧洲的莱茵后枝角鹿(M. rhenanus)存在系统发育亲缘关系；而缩短的脑颅、前端逐渐收缩的基枕骨及较复杂的P4原尖等衍征则表明其属于该属内的进步类群。属内各种的特征对比显示Metacervocerus可能为并系群：山西后枝角鹿(Metacervocerus? shansius)和旁遮普后枝角鹿(Metacervocerus? punjabiensis)保留一些祖征状态(如较长的脑颅、简单的P4形态), 但具有显著直立的角柄和琴形的角冠主枝，暗示其与M. longdanensis存在演化分歧。已发表的同位素数据表明M. longdanensis栖息于半开放环境，具有以食叶到混合食性的生态类型。解决了欧亚鹿亚科长期存在的分类学问题，同时阐明了东亚晚上新世–早更新世时期鹿科演化的生物地理学意义。