Which trait is absent in *Xiongguanlong* nasals but present in *Dilong* and *Eotyrannus*?
Answer
Pneumatic elements along their lateral sides
When examining the nasal bones of *Xiongguanlong*, a key distinction is noted when comparing it to less-derived tyrannosauroid genera, specifically *Dilong* and *Eotyrannus*. While *Xiongguanlong*'s nasals are rostrally fused and slender, they distinctly lack the pneumatic elements—internal air spaces or passages—along their lateral surfaces. These pneumatics are present in the aforementioned earlier genera, indicating that the loss of nasal air spaces was a specific evolutionary step that occurred prior to or concurrent with other skull remodeling in the *Xiongguanlong* stage.
Related Questions
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