A newly published scientific paper highlights the uniqueness and diversity of Australian theropods. The research, published in the Journal of Vertebrate Paleontology identifies the world’s oldest known megaraptorid. In addition, the study provides the first evidence of the presence of carcharodontosaurs in Australia. These fossil discoveries are rewriting the evolutionary history of theropod dinosaurs. Furthermore, they highlight a unique predator hierarchy in Australia during the Early Cretaceous.
The research was led by Museums Victoria Research Institute and Monash University PhD student Jake Kotevski. The scientists describe five new theropod specimens. Three tibiae, and a fossil consisting of two articulated caudal vertebrae with haemal arches, from the upper Strzelecki Group. In addition, the study includes a single tibia from the slightly younger Eumeralla Formation.
Unenlagiinae left tibia (front). Carcharodontosauria left tibia (middle) and Megaraptoridae right tibia (rear). New research highlights the diversity of Early Cretaceous Australian theropods. Picture credit: Nadir Kinani/Museums Victoria.
Picture credit: Nadir Kinani/Museums Victoria
Describing the Theropod Fossils
The five specimens included in the study are:
- Articulated Megaraptoridae caudal vertebrae (NMV P257414) – from upper Strzelecki Group exposures from the Twin Reefs locality.
- A partial right tibia (Megaraptoridae) specimen number NMV P257415 also from upper Strzelecki Group exposures at the Twin Reefs locality.
- Carcharodontosauria indet. left tibia (NMV P186143). A fragmentary fossil collected from the Lesley’s Lair site by Patricia Vickers-Rich in 1988 (upper Strzelecki Group).
- NMV P221042 a Carcharodontosauria indet. right tibia from the Point Lewis locality of the Eumeralla Formation.
- NMV P257601 a crushed left tibia assigned to Unenlagiinae indet. This fossil was found at Eagles Nest, near Inverloch, (upper Strzelecki Group).
For context, the upper Strzelecki Group deposits are dated from 121.4 to 118 million years ago. Whilst the geologically younger Eumeralla Formation dates from 113 to 108 million years ago.
Fragmentary fossil material found in Australia has been assigned to the Megaraptoridae family previously. However, these megaraptorid fossils from the upper Strzelecki Group are several million years older. As such, they are the oldest assigned Megaraptoridae fossil material known to science. Previously, Everything Dinosaur has reported on the discovery of Australian megaraptor fossil material that dates from approximately 110 million years ago.
To read more about this research: Australian Theropod Bone Challenges Gondwana Break-up Theory.
Megaraptoridae right tibia. Picture credit: Nadir Kinani/Museums Victoria.
Picture credit: Nadir Kinani/Museums Victoria
A Fresh Perspective on Australian Theropods
These newly described theropod fossils offer insights into Victoria’s dinosaur dominated, Early Cretaceous ecosystem. The fossils suggest that the apex predators were megaraptorids. In contrast, the coeval carcharodontosaurs were much smaller and lighter. For example, the partial tibia and articulated caudal vertebrae indicate the presence of megaraptorids that were around six to seven metres in length. The fossils assigned to carcharodontosaurs indicate much smaller theropods. A size estimate for the carcharodontosaurs of two to four metres in length has been proposed.
One of the authors of the study, PhD student Jake Kotevski commented:
“The discovery of carcharodontosaurs in Australia is ground-breaking. It’s fascinating to see how Victoria’s predator hierarchy diverged from South America, where carcharodontosaurs reached Tyrannosaurus rex-like sizes up to 13 metres, towering over megaraptorids. Here, the roles were reversed, highlighting the uniqueness of Australia’s Cretaceous ecosystem.”
Two Megaraptoridae caudal (tail) vertebrae and haemal arches. Picture credit: Nadir Kinani/Museums Victoria.
Picture credit: Nadir Kinani/Museums Victoria
Numerous small ornithopods are known from the Early Cretaceous of Victoria. However, sauropod remains are absent. This may have favoured the evolution of smaller, cursorial predators such as megaraptors. Whereas, in South America large carcharodontosaurs were the apex predators. They probably hunted the abundant sauropods. This suggests the composition of the herbivorous dinosaurs in each region led to different theropods dominating the ecosystem.
To read a blog post from 2019 about the discovery of a new ornithopod from Victoria: A New Early Cretaceous Ornithopod from Australia is Described (Galleonosaurus).
Evidence of Faunal Interchange
Co-author Dr Thomas Rich (Museums Victoria) added:
“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. The findings also challenge previous assumptions about body-size hierarchies in Gondwanan predator ecosystems highlighting Victoria’s unique Cretaceous fauna.”
Specimen number NMV P257601 has been referred to the Unenlagiinae. Their taxonomic position within the Theropoda remains controversial. For example, some palaeontologists consider unenlagiines to be a subfamily of the Dromaeosauridae. However, other scientists consider, these small, long-snouted dinosaurs as a separate family (Unenlagiidae). Most unenlagiine fossil remains have been found in South America. Historically, Australia had limited evidence for their presence. Nevertheless, the crushed tibia (NMV P257601) provides further robust evidence for a faunal interchange between South America and Australia across Antarctica.
Jake Kotevski (left) holding Unenlagiinae left tibia and Tim Ziegler (right) holding Megaraptoridae right tibia. Picture credit: Nadir Kinani/Museums Victoria.
Picture credit: Nadir Kinani/Museums Victoria
The Importance of Museum Collections
Co-author Tim Ziegler (Museums Victoria) highlighted the importance of access to museum collections to foster scientific breakthroughs.
He stated:
“Museum collections are crucial to advancing our understanding of prehistoric life. Specimens preserved in the State Collection for decades – unidentifiable until now – are providing new insights into the evolution of dinosaur ecosystems.”
Three of the fossils, uncovered between 2022 and 2023, were first identified by Museums Victoria volunteer Melissa Lowery. This discovery highlights the essential contributions of community members working alongside seasoned researchers to further our understanding of Australia’s Cretaceous past.
An aerial view of Twin Reefs, Bunurong Coastal Reserve (Victoria), the area where some of the dinosaur fossils were found. Picture credit John Broomfield/Museums Victoria.
Picture credit: John Broomfield/Museums Victoria
Everything Dinosaur acknowledges the assistance of a media release from Museums Victoria in the compilation of this article.
The scientific paper: “Evolutionary and paleobiogeographic implications of new carcharodontosaurian, megaraptorid, and unenlagiine theropod remains from the upper Lower Cretaceous of Victoria, southeast Australia” by Jake Kotevski, Ruairidh J. Duncan, Tim Ziegler, Joseph J. Bevitt, Patricia Vickers-Rich, Thomas H. Rich, Alistair R. Evans and Stephen F. Poropat published in the Journal of Vertebrate Paleontology.
The award-winning Everything Dinosaur website: Prehistoric Animal Models.
