Between 2022 and 2023, three new theropod fossils were uncovered, along the coastline in Victoria, Australia. They were first identified by Museums Victoria volunteer Melissa Lowery. Among the finds are two of the oldest known megaraptorids.
"The discovery of carcharodontosaurs in Australia is groundbreaking," said Ph.D. student Jake Kotevski with Museums Victoria Research Institute and Monash University.
According to paleontologists from the Museums Victoria Research Institute and Monash University, during the Early Cretaceous Period, Victoria's ancient ecosystem was dominated by powerful theropods, with large megaraptorids likely holding the dominant predatory role. This contrasts with predator dynamics in South America, where carcharodontosaurs were the apex predators reaching sizes comparable to Tyrannosaurus rex.
Kotevski finds it "fascinating to see how Victoria's predator hierarchy diverged from South America, where carcharodontosaurs reached Tyrannosaurus rex-like sizes up to 13 meters [about 42 feet], towering over megaraptorids. Here, the roles were reversed, highlighting the uniqueness of Australia's Cretaceous ecosystem," as reported by Popular Science.
The fossils were found in geological formations dating back to the Early Cretaceous Period. Specifically, they were found in the upper Strzelecki Group, approximately 121.4 to 118 million years ago, and the Eumeralla Formation, approximately 113 to 108 million years ago.
"The findings not only expand Australia's theropod fossil record but offer compelling evidence of faunal interchange between Australia and South America through Antarctica during the Early Cretaceous," explained Dr. Thomas Rich, senior curator of vertebrate palaeontology at Museums Victoria Research Institute.
Megaraptorids and carcharodontosaurs were theropod dinosaurs—a group characterized by walking on two hind legs and primarily being carnivorous. Megaraptorids belonged to a family of large-bodied dinosaurs from the Cretaceous Period called Megaraptoridae. They are known for somewhat small but sharp teeth, air-filled bones, and powerful forelimbs with enormous claws. These dinosaurs have mostly been found in southern continents.
Carcharodontosaurs, on the other hand, were among the largest land-dwelling carnivores in Earth's history, capable of growing to approximately 45 feet long. While carcharodontosaurs dominated the predator hierarchy in South America, the new findings suggest that in Australia, megaraptorids likely held the dominant predatory role.
"The findings also challenge previous assumptions about body-size hierarchies in Gondwanan predator ecosystems, highlighting Victoria's unique Cretaceous fauna," said Rich, according to Popular Science.
During the Cretaceous Period, Australia was part of the supercontinent Gondwana, along with Antarctica, New Zealand, Africa, India, and South America. As Gondwana began breaking apart, dinosaur evolution changed and diverged. The new findings offer evidence of faunal interchange between Australia and South America through Antarctica during the Early Cretaceous.
The article was written with the assistance of a news analysis system.