Misidentified bones that were stored away in the drawers of a Mongolian institute for half a century have been identified as belonging to a new species of tyrannosaur, shedding light on the evolutionary history of the iconic T-Rex, scientists revealed.

The newly discovered dinosaur species, named Khankhuuluu mongoliensis, is an ancestor of the Tyrannosaurus Rex. These fossils were initially unearthed in southeastern Mongolia in the 1970s but were mistakenly classified as a different tyrannosaur species, Alectrosaurus.

According to a recent study published in the journal Nature, this slender predecessor of the mighty T-Rex measured around four meters in length and weighed three-quarters of a ton, akin to the size of a large horse, as described by study co-author Darla Zelenitsky from the University of Calgary in Canada.

During a visit to Mongolia, Ph.D. student Jared Voris examined the fossils stored at the Institute of Paleontology of the Mongolian Academy of Sciences in Ulaanbaatar and identified them as partial skeletons of two distinct individuals belonging to a previously unknown species.

The newly identified species, Khankhuuluu mongoliensis, provides valuable insights into the complex family tree of tyrannosaurs, clarifying the evolutionary path leading to the T-Rex's reign as the apex predator in North America until the catastrophic asteroid impact 66 million years ago.

It is believed that Khankhuuluu or a closely related relative migrated from Asia to North America via the land bridge connecting Siberia and Alaska, leading to the diversification of tyrannosaurs on the continent. Subsequently, some species returned to Asia, giving rise to different tyrannosaur subgroups, including the smaller Pinocchio rex and the massive Tarbosaurus.

Ultimately, one of these colossal dinosaurs made its way back to North America, evolving into the iconic Tyrannosaurus Rex, which dominated the region for a brief two million years before the catastrophic event that wiped out most life on Earth.

This groundbreaking discovery underscores the importance of reevaluating museum collections worldwide to potentially unveil more hidden treasures that could reshape our understanding of prehistoric life.