Abstract:

The Tyrannosauridae, which is characterized by specialized pachydont dentition and putative bone-cracking predatory strategies, is one of the most extensively studied theropod lineages. Although tooth replacement patterns, crucial for understanding feeding behaviors, have been thoroughly studied in this group, studies on non-tyrannosaurid tyrannosauroids are relatively scarce. This study utilizes high-resolution CT data to investigate the tooth replacement pattern in two specimens of Guanlong wucaii , a Late Jurassic tyrannosauroid, and provides insights into the evolution of tooth replacement across Tyrannosauroidea. Second-generation replacement teeth, a rarity observed mainly in giant predatory theropods (e.g. some tyrannosaurids), were detected in the dentary dentition of the juvenile Guanlong . Zahnreihen reconstructions display a consistent cephalad alternating tooth replacement pattern in the maxilla and the dentary of both of the examined individuals, with Z-spacing values exceeding 2.0. As Guanlong grows, the Z-spacing value in the maxillary dentition increases, resembling the ontogenetic changes documented in the Tyrannosauridae. Additionally, like Tarbosaurus , Guanlong also displays a discontinuity between the tooth replacement waves at the premaxilla-maxilla boundary. This study thus demonstrates that some tyrannosaurid-like tooth replacement patterns were acquired before the origin of the Tyrannosauridae.

Key words: Late Jurassic, Tyrannosauroidea, tooth replacement, 3D reconstruction

摘要：

暴龙科是研究最为深入的兽脚类支系之一，发育极端增厚的齿列，可能具有独特的碎骨捕食策略。与进食行为联系紧密的牙齿替换模式在这一类群中得到了广泛的研究，但前人对早期分异的暴龙超科成员却鲜有相应的研究。利用高分辨率CT数据，三维重建了晚侏罗世暴龙超科——五彩冠龙( Guanlong wucaii )两件标本的齿列，为研究暴龙超科的牙齿替换模式提供了新的信息。五彩冠龙幼年个体的下颌齿列发育二代替换齿，这一特征此前仅在包括暴龙科在内的大型猎食性兽脚类恐龙中有报道。Zahnreihen重建显示，五彩冠龙的两个个体在上颌骨齿和齿骨齿中均表现出Z间距大于2.0的从前向后的波状替换模式。五彩冠龙上颌骨齿的Z间距随着个体发育而变大，与在暴龙科成员中观察到的个体发育变化类似。此外，五彩冠龙在前上颌骨-上颌骨交界处显示出了与特暴龙( Tarbosaurus )相似的牙齿替换波的间断，且这种替换波的间断会随着个体发育加剧。这表明，一些与暴龙科类似的牙齿替换模式在暴龙科起源之前就已经产生。

关键词: 晚侏罗世, 暴龙超科, 牙齿替换, 三维重建