In studying the evolution of vertebrae, biologists have often focused on the notochord, a flexible
rod found in the embryos of all vertebrates. The notochord appears early in development and
is later replaced by the vertebral column, or spine. Because the notochord is essential for the
formation of the spine, it has been argued that the evolution of the spine must have followed
the evolution of the notochord. However, recent research on the lancelet, a small invertebrate
chordate, challenges this view. Lancelets are thought to resemble the ancestors of vertebrates,
and they possess a notochord but lack vertebrae. This suggests that the notochord evolved
before the spine. Moreover, studies of lancelet development have shown that the notochord is
not required for the formation of the tissues that give rise to the spine in vertebrates. Instead,
the notochord appears to play a role in organizing the development of other structures, such as
the nerve cord and the muscles. These findings suggest that the notochord and the spine evolved
independently, with the notochord arising first to serve functions other than spinal development.
The spine may have evolved later as a means of providing support and protection for the body.