The morphology of the cranial thoracic vertebrae has long been neglected in the study of primate skeletal functional morphology. This study explored the characteristics of the third to sixth thoracic vertebrae among various positional behavioural primates. A total of 67 skeletal samples from four species of hominoids, four of cercopithecoids, and two of platyrrhines were used. Computed tomography images of the thoracic vertebrae were converted to a three-dimensional (3D) bone surface, and 104 landmarks were obtained on the 3D surface. For size-independent shape analysis, the vertebrae were scaled to the same centroid size, and the normalised landmarks were registered using the generalised Procrustes method. Principle components of shape variation among samples were clarified using the variance–covariance matrix of the Procrustes residuals. The present study revealed that the transverse processes were more dorsally positioned in hominoids compared to non-hominoids. The results showed that not only a dorsolaterally oriented but also a dorsally positioned transverse process in relation to the vertebral arch contribute to the greater dorsal depth in hominoids than in monkeys. The thoracic vertebrae of Ateles and Nasalis show relatively dorsoventrally low and craniocaudally long vertebrae with craniocaudally long zygapophyses and craniocaudally long base/short tip of the caudally oriented spinous process, accompanied by a laterally oriented and craniocaudally long base of the transverse process. Despite being phylogenetically separated, the vertebral features of Ateles (suspensory platyrrhine with its prehensile tail's aid) are similar to those of Nasalis (arboreal quadrupedal/jumping/arm-swing colobine). The morphology of the third to sixth thoracic vertebrae tends to reflect the functional adaptation in relation to positional behaviour rather than the phylogenetic characteristics of hominoids, cercopithecoids, and platyrrhines.

长期以来，在灵长类骨骼功能形态研究中，颅胸椎的形态一直被忽视。本研究探讨了各种位置行为灵长类动物的第三至第六胸椎的特征。总共使用了来自四种人科动物、四种尾猿和两种桔梗的 67 个骨骼样本。胸椎的计算机断层扫描图像被转换为​​三维 (3D) 骨表面，并在 3D 表面上获得了 104 个地标。对于与尺寸无关的形状分析，将椎骨缩放到相同的质心尺寸，并使用广义 Procrustes 方法注册归一化地标。使用 Procrustes 残差的方差-协方差矩阵阐明样品之间形状变化的主要成分。目前的研究表明，与非人科动物相比，人科动物的横突更位于背侧。结果表明，与脊椎弓相比，不仅背外侧定向而且背侧定位的横突导致人科动物的背侧深度大于猴子。胸椎的Ateles和Nasalis显示相对背腹低和头尾长的椎骨，具有头尾长的关节突和尾侧棘突的头尾长基部/短尖端，伴随着横向突起的横向和头尾长基部。尽管在系统发育上是分开的，但Ateles（悬垂的 platyrrhine 和它的可缠绕尾巴的帮助）的脊椎特征与Nasalis（树栖四足/跳跃/手臂摆动 colobine）的脊椎特征相似。第三至第六胸椎的形态倾向于反映与位置行为相关的功能适应性，而不是人科动物、尾节动物和鸭嘴兽的系统发育特征。