Impressions of the past
Australian scientists studying the smallest known dinosaur footprints, left by a creature the size of a sparrow, also discovered the largest, left by a dinosaur 700,000 times as heavy.
WHILE THE FOSSILISED bones of dinosaurs tell us about the size, shape and anatomy of the animals they once belonged to, fossilised footprints can tell us a whole different story about these animals, revealing clues to prehistoric behaviour.
In 2017 Dr Anthony Romilio of the University of Queensland was part of the team that f irst recorded dinosaur footprints on the coast of the Kimberley in Western Australia that were a whopping 1.7m in length – big enough for many people to lie down inside. These were left by longnecked, herbivorous dinosaurs called sauropods, which walked along river deltas 130 million years ago. Known for centuries by Aboriginal people, these tracks were much bigger than the previous biggest known dinosaur footprints, which measured 106cm across and were discovered the year before in Mongolia’s Gobi Desert.
Now, to complement the exciting 2017 f ind, Romilio, as part of a team that includes South Korean and Chinese scientists, has recorded the smallest dinosaur footprints ever – 1cm-long tracks left by a creature with a hip height of about 4.5cm.
“These new tracks are just 1cm in length, which means the dinosaur that made them was an animal you could have easily held in your hand,” Romilio says. “The diminutive sizes of these new tracks are extraordinary; the tracks were made by tiny dinosaurs about the size of sparrows.”
These are evidence of the smallest dinosaur ever discovered (the previous smallest known dinosaur was a feathered species called Microraptor from China, which was about the size of a crow).
The tracks’ shape reveals they were left by tiny dromaeosaurs – the group of predatory dinosaurs to which Velociraptor, of Jurassic Park fame, belongs. Dromaeosaur tracks are very distinctive, because these animals kept two of the three toes on each foot on the ground, with the third ‘recurved’ claw retracted, a bit like that of a cat. It’s not clear if the animals that left the footprints were babies or adults.
The tracks were found in the Jinju Formation of rocks in South Korea’s Gyeongsang Basin, which is about 129–125 million years old, meaning it’s ver y likely the tiny dinosaurs found here were contemporaries of the truly gigantic dinosaurs we have evidence of in the Kimberley.
Those 1.7m-long prints are among many thousands of dinosaur footprints that have been documented in recent years all the way down that northern part of the coast of WA, by a team including Romilio, as well as his University of Queensland colleague Dr Steve Salisbury.
During the age of the dinosaurs, South America and Australia were joined as part of the supercontinent of Gondwana, which means some species of dinosaurs roamed right across this landmass.
While in WA we only have the footprints of the very largest sauropod dinosaurs, in Argentina there are fossil skeletons, such as that of the recently described species Patagotitan mayorum. Some estimates suggest this titanosaur sauropod would have reached about 37m in length and nearly 64 tonnes in weight – that’s about as heavy as a space shuttle.
Assuming the sauropod footprints in WA were left by dinosaurs that matched that size, and the tiny dinosaurs from South Korea weigh just 100g or less, then the very biggest dinosaurs weighed up to 700,000 times as much as the smallest.
That mind-boggling f igure is testament to the incredible f lexibility of the dinosaur body plan, which could build creatures on such vastly different scales, based on the same basic dinosaur genetic blueprint.
JOHN PICKRELL
is a former AUSTRALIAN GEOGRAPHIC editor. Follow him on Twitter: @john_pickrell