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Re: Spare ribs?
"My guess is [caudal ribs] are the chevrons. Transverse processes are not
chevrons are (as far as I know) homologous to ribs in the tail."
As far as I'm aware, the chevrons are remnants of the haemal arches, bones
that first developed in fishes that provided protection for blood vessels in
the tail. As I know George is aware, chevrons are common in the tails of
many verts, and in sauropods they probably served a function in protecting
blood vessels and such. In some reptiles (snakes, for instance), the
proximal chevrons can act to anchor muscles for sexual reproductive organs.
Chevrons are not homologous to ribs, however, because they are essentially
modified haemal arches and arise below (ventral to) the bodies (centra) of
the vertebrae. Ribs articulate with the centra and transverse processes
Even though transverse processes are not ribs, because ribs generally have
some articulation with the transverse processes, they may get that name in
the sacrum and tail -- at least that's my suspicion.
Hope this helps,
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