Sauropod dorsal vertebra

Volunteer Jim Slezak has been preparing some of our Morrison Formation dinosaur material over the last several years. He recently completed another specimen for us, the small sauropod vertebra shown above. 

The image above is more or less a dorsal view, with anterior to the left. The elongate, rugose areas running lengthwise (parallel to the scale bar) are the surfaces of the neurocentral sutures, where the neural arch attached to the vertebral centrum. Clearly the neural arch is missing (that’s why we can see the sutures), showing that this animal was not fully grown. (See this SV-POW! post for information on the growth of sauropod vertebrae.) The groove between the neurocentral sutures is the bottom of the neural canal, which held the spinal cord.

Above is approximately the right lateral view (this time, anterior is to the right). The big hole at the top center is a real feature, called a pneumatic foramen (pleurocoel in older literature). This is a sinus that in the living animal was filled with part of the air sac system (the respiratory system in saurischian dinosaurs, including birds, works very differently than in mammals). Large pneumatic foramina are present in the cervical, dorsal, and anterior caudal vertebrae of most sauropod taxa. (See this SV-POW! post for information on pneumaticity in sauropods.) The size of the pneumatic foramen and lack of processes on the centrum suggest that this is a dorsal vertebra, perhaps around the 4th or 5th dorsal, but I’m not sure of that, nor am I sure what taxon this represents.

If you’re familiar with sauropod vertebrae, you may have noticed that the shape of this vertebra is a little odd. This bone comes from the “Nickapod” site, which lies close to a fault. The fault has had a rather adverse affect on some of the bones there, which is most obvious in posterior view:

That is a messed-up bone! I’ve oriented it so that the neurocentral sutures are horizontal; consider that the centrum should be close to circular and centered under them. Here’s the same image, with the midline of the vertebra indicated with a red line:

This is a regular problem that we face with the Nickapod material, although even with the deformation we’re able to recover quite a lot of information about these specimens.

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