A newly discovered, tiny T.Rex – a relative of the tyrant king of dinosaurs reveals crucial new information about when and how T. Rex came to as rule the most fearsome of prehistoric predators.
Moros intrepidusa small tyrannosaur who lived about 96 million years ago – during the Cretaceous period – in what was the lush, deltaic environment of what is now Utah. The tyrannosaur, whose name means “harbinger of doom,” is the oldest Cretaceous tyrannosaur species yet discovered in North America, narrowing a 70-million-year gap in the fossil record of tyrant dinosaurs on the continent.
Lindsay Zanno, a palaeontologist at North Carolina State University, head of palaeontology at the North Carolina Museum of Sciences and lead author of a paper describing the research, says: “With a lethal combination of bone-crunching bite forces, stereoscopic vision, rapid growth rates, and colossal size, tyrant dinosaurs reigned uncontested for 15 million years leading up to the end-Cretaceous extinction—but it wasn’t always that way.
“Early in their evolution, tyrannosaurs hunted in the shadows of archaic lineages such as allosaurs that were already established at the top of the food chain.”
Medium-sized, primitive tyrannosaurs have been found in North America dating from the Jurassic (around 150 million years ago), but by the Cretaceous—around 81 million years ago—North American tyrannosaurs had become the enormous, iconic apex predators we know and love.
The fossil record between these time periods has been a blank slate, preventing scientists from piecing together the story behind the ascent of tyrannosaurs in North America.
Zanno says: “When and how quickly tyrannosaurs went from wallflower to prom king has been vexing palaeontologists for a long time.
“The only way to attack this problem was to get out there and find more data on these rare animals.”
That’s exactly what Zanno and her team did. A decade spent hunting for dinosaur remains within rocks deposited at the dawn of the Late Cretaceous finally yielded teeth and a hind limb from the tiny T.Rex.
In fact, the lower leg bones of Moros were discovered in the same area where Zanno had previously found Siats
Despite its diminutive size, Zanno warns that the new specimen was still a
“These adaptations, together with advanced sensory capabilities, are the mark of a formidable predator. It could easily have run down
Zanno continues: “Although the earliest Cretaceous tyrannosaurs were small, their predatory specializations meant that they were primed to take advantage of new opportunities when warming temperatures, rising sea-level and shrinking ranges restructured ecosystems at the beginning of the Late Cretaceous.
“We now know it took them less than 15 million years to rise to power.”
The bones of Moros also revealed the origin of T. rex’s lineage on the North American continent. When the scientists placed Moros within the family tree of tyrannosaurs they discovered that its closest relatives were from Asia.
“T. rex and its famous contemporaries such as Triceratops may be among our most beloved cultural icons, but we owe their existence to their intrepid ancestors who migrated here from Asia at least 30 million years prior,” Zanno says. “Moros signals the establishment of the iconic Late Cretaceous ecosystems of North America.”
The research appears in Communications Biology, and was supported in part by Canyonlands Natural History Association. Lecturer Terry Gates, postdoctoral research scholar Aurore Canoville and graduate student Haviv Avrahami from NC State, as well as the Field Museum’s Peter Makovicky and Ryan Tucker from Stellenbosch University, contributed to the work.