This analysis identifies OMNH 1330 as a likely 4th caudal vertebra, demonstrating distinctive features relevant to apatosaurine morphology.
Here's OMNH 1330, another vertebra from the big Oklahoma apatosaurine. Based on the size and shape of the transverse process, and the large pneumatic chambers on either side of the neural canal, I think this is probably a 4th caudal, but it could plausibly be a 3rd or a 5th.
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Matt Wedel (2018) studied this question.
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