What characteristic is noted for the serrations on the premaxillary teeth of *Xiongguanlong*?
Answer
They lack serrations entirely.
The dentition of *Xiongguanlong* presents a mosaic of traits. Focusing on the teeth situated at the front of the snout, the premaxillary teeth, they share derived features with later tyrannosaurids, such as a D-shaped cross-section and a distinctive median lingual ridge. Crucially, however, these specific teeth are completely devoid of serrations. This lack of serrations on the premaxillary teeth is a feature also observed in juvenile specimens of *Tyrannosaurus rex*, suggesting this particular characteristic might have been lost early in the lineage or only present in early growth stages of derived forms.
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