How did the estimated length of Xiongguanlong compare to Tyrannosaurus rex?

It was significantly shorter, around three meters versus over 12 meters.

There is a stark size disparity between *Xiongguanlong* and its much later relative, *Tyrannosaurus rex*. *Xiongguanlong* is estimated to have been only about three meters long, roughly ten feet in length, reflecting the general medium-to-small size trend of tyrannosaurs during that earlier period. In contrast, *T. rex*, which dominated the Cretaceous world, could exceed 12 meters in length. This immense difference in size, separated by tens of millions of years, highlights that the evolutionary pathway toward extreme gigantism was not continuous or predetermined; rather, the group experimented with different body plans and ecological roles, with *Xiongguanlong* occupying a much smaller predator niche.