Reconstructed body silhouettes of three tyrannosaurs, showing where Xiongguanlong falls in the spectrum of body sizes in this lineage. Dilong on the left is 125 million years old and the smallest known tyrannosaur. Xiongguanlong, shown in grey, is much larger, but is still dwarfed by T. rex, shown on the right. Credit: M. Donnelly/The Field Museum