Perhaps the most iconic dinosaur is tyrant-saury Rex, a massive predator that lived in what is now North America. We have now discovered that carnivorous dinosaurs of a similar size also existed in ancient Australia.
Following in the footsteps
We learned about these carnivores by studying fossils that were discovered up to 90 years ago. Coal miners found them while digging at the Walloon Coal Measures in Rosewood, near Ipswich and Oakey, north of Toowoomba, Queensland.
Fossils are not bones. They are fossilized footprints, the only form of fossil that records the movements of animals and preserves the details of their behavior and the environments they prefer.
While looking at fossil footprint records in Australia, we came across a file photograph from the 1930s showing a dinosaur footprint inside a coal mine. Although these mines have closed a long time ago, the image led us to investigate the fossil footprints collected at that time and stored in museums and other footprints like them.
Greater than T. rex
The specimens we found suggest that the richly forested and swampy environment of southern Queensland in the Jurassic period was home to several types of carnivorous dinosaurs. The smallest would have been the size of an emu, while the largest would be less than 3 meters tall, almost as large and imposing as a Tyrant saurian Rex.
The footprint of this great dinosaur is almost 80 cm long, approximately the distance from the center of its body to the tip of its outstretched arm. The fossilized path is approximately 160 million years old, 90 million years older than the oldest known Tyrant saurian Rex fossil
This suggests that the print belongs to a different predatory dinosaur. While it is similar to Tyrant saurian Rex In terms of size and dietary preference, these massive ancient Australian trackers may have been slimmer and longer in appearance than the North American dinosaur icon.
Fast runners, formidable predators
In addition to the individual tracks, we found evidence of pathways where multiple tracks made by the same animal are preserved. Based on what we know about how two-legged animals move, we can use the tracks to discover how dinosaurs traveled through their environment.
Several of the larger dinosaurs appear to have moved at a walking pace, since the length of their steps is shorter than the estimated length of their legs. However, two tracks had the oversized steps that are typical of animals in the race.
The passing distance suggests that these large dinosaurs were moving at speeds of up to 35 kilometers per hour. For comparison, the average human can run at about 24 kilometers per hour.
These speeds mean that the old track makers would have been formidable predators. Unfortunately, no track was preserved for the largest track maker.
Not all types of terrain are equally suitable for preserving fossilization tracks. What appears to have happened in South Queensland is that the dinosaurs stepped on mats of swamp plant material that was then overlaid with sand, resulting in sandstone footprints in a bed of coal. The miners were able to easily remove the softer coal from under the sandstone and, to their surprise, found these ancient footprints.
If it weren’t for coal mining and the sharp eyes of 20th-century miners who spotted unusual features in the rock, we might never have known about these tracks. More hidden treasures are likely still buried under our feet.
Filling the gaps in ancient Australia
Our discovery fills a gap in the slow growth of Australian dinosaurs. While large dinosaur footprints have been documented in several Australian states, so far most belong to plant eaters. They include footprints of long-necked sauropods similar to Brontosaurusand ornithopods similar to Muttaburrasaurus, whose skeleton can be seen on display at the Queensland Museum.
There is also evidence of carnivorous dinosaurs, but so far the fossil record has indicated much smaller animals, from the size of chickens to slightly smaller than Allosaurus.
Our discovery of the tracks of a large carnivore adds a major high-level predator to the Australian dinosaur landscape.
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