Table_2_The Tail of the Late Jurassic Sauropod Giraffatitan brancai: Digital Reconstruction of Its Epaxial and Hypaxial Musculature, and Implications for Tail Biomechanics.XLS

Dinosaur locomotion and biomechanics, especially of their pelvic girdles and hindlimbs, have been analyzed in numerous studies. However, detailed volumetric musculoskeletal models of their tails are rarely developed. Here, we present the first detailed three-dimensional volumetric reconstruction of the caudal epaxial and hypaxial musculature of the Late Jurassic sauropod Giraffatitan brancai, and highlight the importance and necessity of 3D modeling in musculoskeletal reconstructions. The tail of this basal macronarian is relatively short compared to diplodocids and other coexisting macronarians. The center of mass lies well in front of the hindlimbs, which support only ca. half the body weight. Still, our reconstruction suggests a total weight for the entire tail of ca. 2500 kg. We conclude that the hypaxial and tail-related hindlimb muscles (most specifically the M. caudofemoralis longus and its counterpart the M. ilioischiocaudalis) in Giraffatitan were well developed and robustly built, compensating for the shorter length of the M. caufodemoralis longus, the main hindlimb retractor muscle, in comparison with other sauropods. Our methodology allows a better-constrained reconstruction of muscle volumes and masses in extinct taxa, and thus force and weight distributions throughout the tail, than non-volumetric approaches.

诸多研究已针对恐龙的运动模式与生物力学特性展开分析，其中尤以骨盆带与后肢相关内容为重点。然而，针对其尾部的精细化体积式肌肉骨骼模型却鲜有构建。本研究首次实现了晚侏罗世蜥脚类恐龙布氏长颈鹿龙（Giraffatitan brancai）的尾部轴上与轴下肌肉群的三维体积重建，并阐明了三维建模在肌肉骨骼重建中的重要性与必要性。相较于梁龙类与其他同期大鼻龙类，这类基干大鼻龙类的尾部相对较短。其重心显著位于后肢前方，而后肢仅承担约一半的体重。尽管如此，本次重建结果显示整条尾部的总重量约为2500千克。我们推断，布氏长颈鹿龙的轴下肌肉与尾部相关后肢肌肉（尤以长股骨尾肌（M. caudofemoralis longus）及其对应肌肉坐尾肌（M. ilioischiocaudalis）为代表）发育程度高且结构强健，弥补了相较于其他蜥脚类恐龙时长股骨尾肌这一主要后肢牵缩肌长度偏短的缺陷。相较于非体积式研究方法，本研究采用的方法能够对灭绝类群的肌肉体积与质量进行约束性更强的重建，进而更精准地推断整条尾部的受力与重量分布情况。