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Re: Spare ribs?

Hi George.

Dinogeorge writes:

"My guess is [caudal ribs] are the chevrons. Transverse processes are not ribs, but
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 instead.

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,

Matt Bonnan
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