URL: https://www.bbc.com/news/articles/cy8dzv3vp5jo
Researchers concluded that two 86 million-year-old skeletons they studied belonged to a species that is now the closest known ancestor of all tyrannosaurs - the group of predators that includes the iconic T.rex.
The researchers named the species Khankhuuluu (pronounced khan-KOO-loo) mongoliensis, meaning Dragon Prince of Mongolia.
Khankhuuluu represents an evolutionary shift - from those small hunters that scampered around during the Jurassic period - to the formidable giants, including T.rex.
It would have weighed about 750kg, while an adult T.rex could have weighed as much as eight times that, so "this is a transitional [fossil]," explained Prof Zelenitsky, "between earlier ancestors and the mighty tyrannosaurs".
Mr Voris explained: "That movement back and forth between the continents basically pushed the evolution of different tyrannosaur groups" over millions of years.
Prof Zelinitsky added: "This discovery shows us that, before tyrannosaurs became the kings, they were princes."