Unformatted text preview: were large! Dunkeleosteous: 9 meters long, major predator A note on the evolution of bone
•! Regarding the positions of vertebrae and bone on the
vertebrate cladogram, organisms can have vertebrae made
out of cartilage. This is what occurs in lampreys. They
are not vertebrae in the sense of the human skeleton, but
they are bits of cartilage that sit above the notochord as
neural arches or spines. Lampreys do not have bone.
•! Professor Wainwright says: Cartilage is not necessarily an
ontogenetic or evolutionary precursor of bone. It's a versatile,
high performance skeletal material in its own right. Of
course there are many adult cartilaginous structures, but
also, lots of bones do not develop by replacing cartilage (all
dermal bones for example). A number of non-vertebrate
metazoans have cartilage and no bone (molluscs are a good
•! Professor Wainwright also says that bone first occurred in the
dermal skull of ostracoderms, a paraphyletic group, but even
there it was not in the vertebrae (these were cartilaginous)....
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This document was uploaded on 04/13/2013.
- Fall '08