What specific major jaw component was notably lacking from the holotype specimen of *Xiongguanlong*?
Answer
The lower jaws.
The holotype specimen, FRDC-GS JB16-2-1, provides an extensive but not entirely comprehensive view of the dinosaur's skeleton. While it includes key elements necessary for detailed study, such as a complete skull, the entire series of neck and back vertebrae, and parts of the right hip and femur, one significant portion of the skull apparatus is explicitly mentioned as missing: the lower jaws. This absence means that direct analysis of the dentary and other lower jaw structures must rely on comparative anatomy with related species.
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