AI 中文总结
本研究通过定量与定性方法分析两种矮象化石的四肢长骨，发现矮象并非大陆祖先的按比例缩小版，而是兼具幼态、承重与祖先特征，揭示了矮化对长鼻类演化轨迹的影响。
AI 中文摘要
陆生脊椎动物依靠骨骼提供结构支撑并实现躯体运动。现存象类等重型承重类群的骨骼解剖结构具有诸多适应性特征，使其能承受巨大体重。相反，矮化事件会对骨骼施加全新的生物力学约束。矮象的案例提出了一个问题：承重动物在经历剧烈体型缩小的过程中如何适应，是保留承重特征还是表现出幼态特征？本研究采用定量与定性相结合的方法（3D几何形态测量学、虚拟切片对比、密质骨厚度图谱），对两种矮象化石物种——tiliensis古菱齿象（成年个体）和falconeri古菱齿象（幼年个体）的六块长骨的形态与显微结构进行研究。结果显示，tiliensis古菱齿象的体重减轻反映在骨骼形态与显微结构上，与完全承重的长鼻类相比，其四肢姿势更弯曲，矢状面定向性降低。尽管存在这种转变，tiliensis古菱齿象仍保留了若干关键的承重适应性特征。此外，与早期非承重长鼻类的对比表明，矮象表现出部分向祖先四肢特征的回复，同时保留了基本的承重特征。最后，成年tiliensis古菱齿象与幼年falconeri古菱齿象标本的髓腔区域充满骨小梁，与现存象类相似。因此，矮象并非其大陆祖先的按比例缩小版本，而是展现出幼态、承重与祖先特征的组合，反映了矮化对其演化轨迹的影响。
英文摘要
Terrestrial vertebrates rely on their skeleton to provide structural support and allow the movement of the body. Heavy, graviportal taxa, such as extant elephants, exhibit numerous adaptive features in their bone anatomy enabling them to withstand their immense weight. Conversely, dwarfing events impose novel biomechanical constraints on the skeleton. The case of dwarf elephants raises the question of how graviportal animals adapt when undergoing drastic size reduction, and whether they retain graviportal features or exhibit paedomorphic traits. In this study, we examine the morphology and microanatomy of the six long bones in two fossil species of dwarf elephants, Palaeoloxodon tiliensis (adults) and P.___falconeri (juveniles), using both quantitative and qualitative approaches (3D geometric morphometrics, virtual slice comparisons, compact bone thickness cartographies). Our results show that in P.___tiliensis , the reduction in body mass is reflected in the morphology and microanatomy of the bones, suggesting a more flexed limb posture and a reduced parasagittal orientation compared to in fully graviportal proboscideans. Despite this shift, several key graviportal adaptations are retained in P.___tiliensis . Additionally, comparisons with early, non-graviportal proboscideans indicate that dwarf elephants exhibit a partial reversion to ancestral limb traits, while maintaining essential weight-bearing features. Finally, adult P.___tiliensis and juvenile P.___falconeri specimens exhibit a medullary area filled with trabecular bone, similar to that of extant elephants. Dwarf elephants are thus not scaled-down versions of their mainland ancestors, but instead display a combination of juvenile, graviportal and ancestral traits reflecting the impact of dwarfism on their evolutionary trajectory.
Journal refPalaeontology, 2026, 69 (3)
