The modern human thoracic vertebral section exhibits a convex or outwardly bulging curvature. This is one of the curves in the spine that positions the torso directly over the hip joints, enabling an erect posture for bipedal locomotion. Chimpanzees differ from modern humans in that they lack the convex curvature of the thoracic region.

Modern human thoracic vertebrae are characterized by short centra (bodies) and inferiorly-directed spinous process, which are positioned higher up on the centra. Chimpanzees have longer spinous and transverse processes when compared to modern humans. The chimpanzee spinous process projects dorsally compared to the downward direction of modern humans.

The inferior articular processes in human thoracic vertebrae are larger than the superior articular processes; the superior articular process in chimpanzees is more pronounced than the inferior articular process.

Lucy’s thoracic vertebrae are a combination of chimpanzee and modern human features. Lucy’s thoracic vertebral section exhibits the human-like convex curvature. Her thoracic vertebral bodies are intermediate in size between chimpanzees and humans. Her vertebrae have long spinous and transverse processes and the superior and inferior articular facets appear almost equal in size. The direction of the Lucy’s spinous process is unclear. While not identical to modern humans, Lucy’s thoracic vertebrae are more similar to modern humans than chimpanzees.