intercentra

Intercentrum is a skeletal element of the vertebral column found in some vertebrates, particularly in early vertebrates and some amphibians. It is one of the ossification centers that can contribute to the vertebral body, traditionally described together with the pleurocentrum. In many lineages, the two centers either fuse to form a single composite centrum or the intercentrum becomes reduced or absent, leaving the pleurocentrum as the main component of the vertebral body.

Variation across taxa is notable. In many amphibians, both intercentrum and pleurocentrum are present and contribute to the vertebral centrum, whereas in most amniotes (reptiles, birds, mammals) the intercentrum is vestigial or absent and the centrum is formed primarily by the pleurocentrum. In several extinct fishes and early tetrapods, intercentra persist as distinct elements alongside pleurocentra, reflecting an ancestral condition.

Developmentally, intercentra arise as separate ossification centers during embryonic development and may later fuse with the pleurocentrum as the vertebra matures. Functionally, they contribute to the anterior-posterior dimensions of the vertebral body and participate in articulations with adjacent vertebrae and, in many thoracic regions, with ribs.

In paleontology and comparative anatomy, the presence, size, and fusion of intercentra versus pleurocentra inform interpretations of vertebral evolution and relationships among early gnathostomes and tetrapods. The shift toward a single vertebral centrum argumentatively marks a major trend in the evolution of the vertebral column in crown tetrapods.