What characteristic of the axial neural spine is shared with more derived tyrannosaurids?
Answer
It is expanded with distinct processes at its corners.
The morphology of the axis vertebra (the second cervical vertebra) in *Xiongguanlong* provides evidence of its derived nature in some respects. Specifically, the axial neural spine exhibits an expanded structure. Furthermore, this expanded spine features distinct processes located at its corners. This particular feature is recognized as a hallmark characteristic typically associated with the more derived tyrannosaurids, such as those found in the Late Cretaceous, suggesting that this structural development in the upper neck evolved relatively early in the lineage's progression.
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