Spine
From EvoWiki
The spine (or spinal column or vertebral column) is a column of successive vertebrae, found (by definition) in all vertebrates.
Evolution
The verterbal column evolved from the notochord - a rod of cells within a firm sheath, located ventrally to the spinal cord. This structure is present in a few extant vertebrates, such as hagfish and lampreys - as well as in the embryo of all vertebrates. It functions to resist compressive forces during swimming. While hagfish have no spinal elements, lampreys have small cartilaginous arches (arcualia) partially encasing their spinal cord, as do extinct species like hetorostracans and osteocrans. As such arches developed further, they would fully surround the notochord, as they do in sturgeons, providing further resistance to compressive forces generated in swimming. With the pressure to swim faster, the centra of the vertebrae would have developed, enveloping the notochord completely, as in chondrichthyans (eg. sharks), and eventually take over the function of the notochord completely. As ribs developed to strengthen the body, the demands on the vertebral axis were increased, causing the development of a fully ossified (boney) spinal column, as is present in extant Osteichthian fishes.
References
- Liem K.F, Bemis W.E, Walker W.F Jr, and Grande L. (2001), Functional anatomy of the vertebrates : an evolutionary perspective, Harcourt College Publishers, Third Edition, pp270-93
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This page is part of the EvoWiki Encyclopedia of Anatomy and Physiology. |
