Top: Xiongguanlong, the perfect fit. Left, Dilong paradoxus from ~125 million years ago, center, Xiongguanlong baimoensis from ~125–100 million years ago, right, Tyrannosaurus rex from ~66 million years ago. M. Donnelly/The Field Museum.
Bottom: Comparison of skull shape between the deep Tyrannosaurus rex skull (left) and the short and slender Xiongguanlong baimoensis skull (right). Skulls are not to scale.