Paleontologists have identified a new species of dinosaur named Khankhuuluu mongoliensis, discovered from fossils originally unearthed in Mongolia in the 1970s. This species, dating back approximately 85 to 86 million years, is considered the closest-known ancestor to the Tyrannosaurus rex, filling a critical gap in the tyrannosaur family tree. The dinosaur, nicknamed the "Dragon Prince of Mongolia," was smaller-bodied, weighing around 750 kilograms, and exhibited agility, contrasting with the later giant T. rex predators. This discovery redefines the evolutionary history of tyrannosaurs by bridging the gap between small early tyrannosaurs and the large apex predators they eventually became. Additional findings include a recently unearthed dog-sized dinosaur from Colorado, dating to about 150 million years ago, which adds to the understanding of dinosaur diversity but is separate from the Khankhuuluu discovery. The Khankhuuluu mongoliensis fossils had been misidentified and stored in museum collections for decades before being reclassified, highlighting the importance of revisiting archived specimens in paleontology.