A tiny Tyrannosaurus nicknamed the "Omen of Fate" was discovered in Utah

Tyrannosaurus rex has not always been the king of dinosaurs. Before becoming large predators, tyrannosaurs initially had a much smaller size, and a newly discovered fossil helps bridge the gap between these two extremes.

Fossil finds are detailed in a study published Thursday in Communications Biology.

The dinosaur fossil was discovered in Utah, where he lived 96 million years ago in a lush delta during the Cretaceous period. It's called Moros intrepidus, which means "the omen of fate". The dinosaur lived at the end of the reign of the allosaurs at the top of the food chain and before the arrival of Tyrannosaurus rex.

It is now the oldest Tyrannosaurus of the Cretaceous period of North America.

Medium-sized Tyrannosaur fossils date back to the Jurassic period, about 150 million years ago. And then, about 81 million years ago, during the Cretaceous, tyrannosaurs became giant predators and replaced allosaurs at the top of the food chain.

So what happened between the two? Moros helps researchers bridge this gap of 70 million years and paint a portrait of the lineage of Tyrannosaurs in North America. Moros connects the oldest and the smallest tyrannosaurs to Tyrannosaurus rex.

"With a murderous combination of biting forces, a stereoscopic vision, rapid growth rates and a colossal size, the tyrant dinosaurs ruled for 15 million years, unquestionably, up to # 1. 39 at the final Cretaceous extinction – but this was not always the case "Lindsay Zanno, lead author of the study and paleontologist at North Carolina State University, in a statement. "When and how the tyrannosaurs went from wallflower to prom king, it has long frustrated paleontologists. The only way to tackle this problem was to go there and find more information about these rare animals. "

Zanno and his team spent a decade looking for Upper Cretaceous fossils. They recovered teeth and a hind limb consisting of a femur, a shin and parts of a foot belonging to Moros in the same area where Zanno found the fossil of a carnivorous carcharodontosaurus giant.

But Moros was between 3 and 4 feet tall. The dinosaur they found was 7 years old when he died, an almost adult adult who would have weighed about 172 pounds. The bones of the leg and the elongated foot indicated that he would be an excellent runner.

"Moros was light and unusually fast," said Zanno. "These adaptations, combined with advanced sensory abilities, are the mark of a formidable predator. He could easily have shot prey, while avoiding confrontation with the big predators of the day. "

This allowed Moros to be a survivor as the environment changed. For 15 million years, tyrannosaurs were restricted to this reduced size before becoming giants (about 12 feet tall and 11,000 to 15,500 pounds) over a period of 16 million years.

"Although the first Cretaceous tyrannosaurs are small, their predatory specialization has allowed them to be ready to take advantage of the new opportunities offered by warmer temperatures, rising sea levels and the reduction of distribution chains in the early late Cretaceous, "Zanno said. "We now know that it took them less than 15 million years to gain power."

Moros is very close to the tyrannosaurs of Asia, which allowed the researchers to trace the lineage of the dinosaurs. This means that Moros crossed the Alaska land bridge during early Cretaceous to reach North America.

"T. Rex and his famous contemporaries such as Triceratops may be among our most valued cultural icons, but we owe their existence to their intrepid ancestors who emigrated from Asia at least 30 million years ago, "he said. said Zanno. "Moros signals the establishment of the iconic ecosystems of the Upper Cretaceous of North America."