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A remarkable Early Jurassic record has been hiding in plain sight for 20 years on a slab of rock displayed at a high school in Biloela, Australia, according to a new study.
While researchers knew the 1.5-meter-long (about 5-foot-long) slab was around 200 million years old and home to an abundance of visible dinosaur footprints, the significance of the fossil remained unclear.
Now, a team of paleontologists studying the rock’s surface has found 66 fossilized footprints from 47 individual dinosaurs belonging to the ichnospecies Anomoepus scambu. Ichnospecies are organisms identified only through trace fossils, or fossils that are of impressions they leave, such as footprints, rather than the actual organisms.
The discovery represents one of the highest concentrations of dinosaur footprints per square meter ever documented in the country, and it provides an “unprecedented snapshot” of the abundance of dinosaurs during the Early Jurassic, a period during which no dinosaur bones have been uncovered in Australia, according to a news release from The University of Queensland. The findings were published in the journal Historical Biology on March 10.
The fact that this fossil slipped under the radar for decades isn’t surprising, said lead study author Dr. Anthony Romilio, a paleontologist and research associate with the university’s Dinosaur Lab.
The footprints show the dinosaurs walking in two directions, likely depicting a crossing at a river. – Courtesy The University of Queensland
“Fossil dinosaur footprints tend to be vastly under-rated even by many (paleontologists),” Romilio said in an email.
But in Australia, since the oldest fossilized dinosaur bones come from the Middle Jurassic, about 160 million years ago, “footprint fossils are the only direct evidence our country has of the types of dinosaurs we had here (during earlier times),” Romilio said. What’s more, the slab provides a rare glimpse into the behavior and activity of a dinosaur that has only been described by its footprints found in various parts of the world, experts say.
Dinosaur footprints from Early Jurassic
By using advanced 3D imaging and light filters, Romilio was able to uncover hidden details in the stone slab, revealing the multitude of footprints and other features such as the direction in which the animals that made the tracks were headed.
The 66 fossilized footprints, which range in size from about 5 centimeters to 20 centimeters (about 2 to 8 inches) in length, reveal that the dinosaurs had likely been crossing a river or going up and down the length of a river, Romilio said. Since there are no ripple marks on the surface of the rock, it is difficult to tell the river flow’s direction, but the tracks clearly show the dinosaurs walking in two directions, he added.
Through his analysis, Romilio found a total of 13 sequences of footprints that belonged to 13 dinosaurs that made the trackways. The remaining footprints, coming to a total of 34, were classified as isolated footprints, accounting for the 47 total individuals. The dinosaurs that made the tracks would have had legs ranging from 15 to 50 centimeters (about 6 to 20 inches) in length along with a chunky body and short arms, Romilio said.
Although trace fossils are often overlooked because they are more common than dinosaur bones, they can “provide a huge amount of information when they’re properly analyzed,” said Dr. Paul Olsen, a paleontologist and Arthur D. Storke Memorial Professor of Earth & Environmental Sciences at Columbia University. Olsen, who has studied Anomoepus, was not involved with this new study.
“(Footprints) provide information about animals that were present even though we don’t have the bones … They’re really like a parallel dataset that allows us to track, pun intended, what’s going on when the bones are rare. That’s why they’re so important,” Olsen said.
From what is known about the other tracks that have been found across parts of the US, Europe, Africa and China, A. scambus was a three-toed, two-legged dinosaur that belonged to the ornithischian family, which includes other plant-eating dinosaurs such as duckbills and triceratops, and had beaks at the front of their mouths with grinding teeth, Olsen said.
These new footprints, which preserve a lot of anatomical detail, further support that “small ornithischian dinosaurs achieved a global distribution by the beginning of the Jurassic Period,” he added.
Hidden in plain sight
The study authors also analyzed two other instances of trace fossils that were found in unexpected locations. They found that a 2,000-kilogram (about 4,400-pound) boulder used as a parking lot entry marker at the Callide mine near Biloela had two distinct footprints left by a slightly larger dinosaur. And a third rock from a personal collection (in use as a bookend) had a single footprint.
The researchers also analyzed a boulder being used as a parking lot entry marker at the Callide mine near Biloela. The rock has two distinct footprints left by a slightly larger dinosaur. – Courtesy The University of Queensland
The rock slab located at the high school was also originally from the Callide Mine, which is an open-cut mine, meaning that the overlying rock is removed to get to the coal underneath, Romilio explained. During the extraction of the overlying rock, which spans many miles and dates to the Early Jurassic period, fossil footprints such as these can be found.
“There are definitely many more fossils occurring there,” Romilio said. “Whether they are spotted in time, or whether it is safe to pick them up is another thing entirely. We are just lucky that these and some others have been spotted, recovered and available for people like me to study them and share the findings.”
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