A recent discovery in Australia has reshaped the understanding of the ancient ecosystem that existed approximately 120 million years ago. Paleontologists have unearthed fossils of two formidable predatory dinosaurs that coexisted, challenging previous assumptions regarding their ecological roles. Among the significant findings is the earliest known large megaraptor, marking a crucial addition to the fossil record.
Megaraptorids, a group of predatory dinosaurs that thrived during the Cretaceous period (145 million to 66 million years ago), were known for their dominance in regions that are now part of Australia and South America. These continents were once linked through Antarctica, forming part of the vast southern supercontinent, Gondwana.
Jake Kotevski, the lead author of the study and a paleontology doctoral candidate at the Museums Victoria Research Institute and Monash University in Australia, described megaraptorids as “hands-first predators.” These dinosaurs possessed robust forelimbs equipped with elongated, curved claws designed for capturing prey. Kotevski likened their hunting strategy to a “hug of death,” a lethal grasp used to subdue their victims. The newly discovered fossils belonged to an unidentified megaraptorid species that measured between 6 and 7 meters (ca. 23 ft to 23 feet) in length, classifying it as one of the largest theropods ever found in Australia. Additionally, the specimen predates South American megaraptorids by approximately 30 million years.
The study, published on February 19 in the Journal of Vertebrate Paleontology, also identified fossils from a distinct group of predatory dinosaurs known as carcharodontosaurs. The discovery of these dinosaurs in Australia is a first, despite their previous documentation in South America. The findings indicate that carcharodontosaurs in this region grew to about 4 meters (ca. 13 ft feet) in length, significantly smaller than their South American relatives, which could reach up to 13 meters (ca. 43 ft feet).
These findings suggest that, in contrast to the ecological hierarchy observed in South America, the predator roles in ancient Australia were reversed. In this region, megaraptorids appeared to function as apex predators, whereas carcharodontosaurs occupied a secondary predatory role. This “upside-down” dynamic, as described by Museums Victoria, highlights the unique nature of Australia’s Cretaceous ecosystem.
The fossils were recovered from the upper Strzelecki rock formation along the southern coastline of Victoria. Excavations took place over a period spanning from 1988 to 2022, with the specimens extracted from what was once a major riverbank. This ancient waterway, comparable to the modern Amazon or Ganges rivers, provided a thriving habitat for diverse species, including numerous smaller dinosaurs. During the Cretaceous period, southern Australia was positioned within the Antarctic Circle. However, the climate at the time was considerably warmer than it is today, supporting a rich and varied ecosystem.
To analyze the fossils, researchers utilized advanced 3D imaging techniques, including micro-computed tomography. This method, which involves capturing X-ray images as the object rotates 360 degrees, enabled the team to examine the specimens in exceptional detail. Their findings confirmed the coexistence of megaraptorids and carcharodontosaurs along the riverbanks within a vast rift valley. Australia gradually separated from Tasmania and Antarctica, forming this valley.
According to Kotevski, the region likely experienced extended periods of darkness and daylight, akin to modern polar conditions. Thick forests lined the river, providing a suitable habitat for various small dinosaur species. Taking advantage of the many smaller animals, the apex megaraptorid predator dominated the ecosystem.
These discoveries contribute to growing evidence that dinosaurs migrated across Antarctica, facilitating the exchange of species between South America and Australia during the mid-Cretaceous period. Despite these significant findings, researchers acknowledge that much remains to be uncovered about the prehistoric ecosystem of Australia.
Kotevski emphasized the importance of continued research, excavation, and analysis to further unravel the mysteries surrounding these ancient creatures. Ongoing discoveries will enhance the understanding of how these species evolved, interacted, and adapted to their environment millions of years ago.
