Chinzorig Tsogtbaatar, Takasaki Ryuji, Yoshida Junki, Tucker Ryan T, Buyantegsh Batsaikhan, Mainbayar Buuvei, Tsogtbaatar Khishigjav, Zanno Lindsay E
Department of Biological Sciences, North Carolina State University, Raleigh, NC, USA.
Institute of Paleontology, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia.
Nature. 2025 Sep 17. doi: 10.1038/s41586-025-09213-6.
The dome-headed pachycephalosaurians are among the most enigmatic dinosaurs. Bearing a hypertrophied skull roof and elaborate cranial ornamentation, members of the clade are considered to have evolved complex sociosexual systems. Despite their importance in understanding behavioural ecology in Dinosauria, the absence of uncontested early diverging taxa has hindered our ability to reconstruct the origin and early evolution of the clade. Here we describe Zavacephale rinpoche gen. et sp. nov., from the Lower Cretaceous Khuren Dukh Formation of Mongolia, the most skeletally complete and geologically oldest pachycephalosaurian discovered globally. Z. rinpoche exhibits a well-developed frontoparietal dome and preserves the clade's first record of manual elements and gastroliths. Phylogenetic analysis recovered Z. rinpoche as one of the earliest diverging pachycephalosaurians, pushing back fossil evidence of the frontoparietal dome by at least 14 Myr and clarifying macroevolutionary trends in its assembly. We found that the earliest stage of dome evolution occurred by means of a frontal-first developmental pattern with retention of open supratemporal fenestra, mirroring proposed ontogenetic trajectories in some Late Cretaceous taxa. Finally, intraskeletal osteohistology of the frontoparietal dome and hindlimb demonstrate decoupling of sociosexual and somatic maturity in early pachycephalosaurians, with advanced dome development preceding terminal body size.
圆顶头的厚头龙类恐龙是最神秘的恐龙之一。该类群的成员有着肥厚的颅顶和精致的颅骨装饰，被认为已经演化出了复杂的社会性别系统。尽管它们对于理解恐龙行为生态学很重要，但缺乏无争议的早期分支类群阻碍了我们重建该类群起源和早期演化的能力。在此，我们描述了来自蒙古下白垩统呼仁杜赫组的仁波切圆顶龙（Zavacephale rinpoche），这是全球发现的骨骼最完整且地质年代最古老的厚头龙类恐龙。仁波切圆顶龙具有发育良好的额顶圆顶，并保留了该类群手部元素和胃石的首个记录。系统发育分析将仁波切圆顶龙恢复为最早分化的厚头龙类恐龙之一，将额顶圆顶的化石证据至少推前了1400万年，并阐明了其形成过程中的宏观演化趋势。我们发现，圆顶演化的最早阶段是通过额部优先的发育模式发生的，同时保留开放的颞上孔，这与一些晚白垩世类群所提出的个体发育轨迹相呼应。最后，额顶圆顶和后肢的骨骼内组织学表明，早期厚头龙类恐龙的社会性别成熟和躯体成熟是解耦的，圆顶的高度发育先于最终体型。
