"bone of the spine," early 15c., from Latin vertebra "joint or articulation of the body, joint of the spine" (plural vertebræ), perhaps from vertere "to turn" (from PIE root *wer- (2) "to turn, bend") + instrumental suffix -bra. The notion would be the spine as the "hinge" of the body.
-al 1
suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).