Hezhengia bohlini is one of the extinct bovids with the most abundant material, especially skulls. To date, skulls have been described, and the phylogenetic relationships and dietary habits have been discussed, but the ontogenetic processes of this special bovid with robust horn cores and a heavily built cranium have not yet been explored. Intraspecific variation in H. bohlini is high, but the variation ranges of different parts of the skull are unknown. In this study, we took 28 measurements and distinguished five age stages from sub-adult to senile. We described the ontogeny of the horn core, dentition, and skull and compared allometric growth and intraspecific variations of different parts of the skull. Although horn core growth and cranial roof arching are supposed highly related, horn core robustness is not related to cranium shape, basioccipital size, nor skull length or width. The rapid horn core growth of H. bohlini occurs in a very short period, from sub-adult to adult, whereas minor modifications and the deposition of exostoses are lifelong processes. The ontogenetic trajectory of H. bohlini differs from that of the closely related urmiatherine, Urmiatherium intermedium, in its late horn core development and cranial roof elevation, but characteristic features of basicranium development are only slightly different in both species. This study not only provides a good model for the study of ontogenetic and intraspecific variations in fossil bovids but also provides a framework for classifying other bovids known from fewer materials.

Hezhengia bohlini是已灭绝的牛科动物之一，材料最丰富，尤其是头骨。迄今为止，已经描述了头骨，并讨论了系统发育关系和饮食习惯，但尚未探索这种具有坚固角核和重型颅骨的特殊牛科动物的个体发育过程。H. bohlini 的种内变异高，但颅骨不同部位的变异范围未知。在这项研究中，我们进行了 28 次测量并区分了从亚成人到老年的五个年龄阶段。我们描述了角核、牙列和颅骨的个体发育，并比较了颅骨不同部位的异速生长和种内变异。尽管角核的生长和颅顶拱形被认为高度相关，但角核的坚固性与颅骨形状、基底枕骨大小、颅骨长度或宽度无关。H. bohlini的快速角核生长发生在很短的时间内，从亚成虫到成虫，而微小的改变和外生骨赘的沉积是终生的过程。H. bohlini的个体发育轨迹不同于密切相关的 urmiatherine，Urmiatherium intermedium，其角核发育后期和颅顶抬高，但两种物种的basicranium发育特征仅略有不同。这项研究不仅为研究化石牛科动物的个体发育和种内变异提供了一个很好的模型，而且还为从较少的材料中对已知的其他牛科动物进行分类提供了一个框架。