As a child, any millennial remotely interested in dinosaurs (how many of us weren’t, really?) would have grown up with “longneck” Littlefoot and his friends in The Land Before Time. Sidestepping for a moment the years of emotional trauma caused by that scene (if you know, you know), Littlefoot’s name leads to a very apposite question. How did Littlefoot’s Apatosaurus family and other massive sauropod dinosaurs carry their colossal weight on their feet?
Sauropods were not only the largest of the dinosaurs, the long-necked, small-headed behemoths were the largest land animals of all time. The largest like Dreadnoughtus and Argentinosaurus are estimated to have grown to 30 or 40 metres in length and weighed in at anywhere between 50-100 tonnes.
The biomechanics of lugging all that weight around on land is no mean feat and palaeontologists have been scratching their heads about it for years.
In fact, it has led many palaeontologists in the past to suggest that the only way sauropods could have carried their own weight around is if they were semi-aquatic animals with their weight supported by water. This theory was disproved in the mid-20th century by the discovery of fossilised sauropod tracks that were laid down on prehistoric land.
Research from University of Queensland (UQ) and Monash University might have cracked the case using 3D modelling and engineering methods to reconstruct and test the foot structures of different sauropods. The team’s findings are published in Science Advances.
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Leading the research as part of his PhD at UQ, Dr Andreas Jannel says the results show sauropods evolved a soft tissue “pad” beneath the heels on their hind feet. This pad would have cushioned the foot to absorb their immense weight.
“We’ve finally confirmed a long-suspected idea and we provide, for the first time, biomechanical evidence that a soft tissue pad – particularly in their back feet – would have played a crucial role in reducing locomotor pressures and bone stresses,” Jannel says. “It is mind-blowing to imagine that these giant creatures could have been able to support their own weight on land.”
“Popular culture like Jurassic Park or Walking with Dinosaurs often depicts these prehistoric mammals with almost-cylindrical, thick, elephant-like feet,” adds co-author Dr Olga Panagiotopoulou from Monash. “But when it comes to their skeletal structure, elephants are actually ‘tip-toed’ on all four feet, whereas sauropods have different foot configurations in their front and back feet. Sauropod’s front feet are more columnar-like, while they present more ‘wedge high heels’ at the back supported by a large soft tissue pad.”
The difference between elephant and sauropod feet is dueto their very different evolutionary paths according to the researchers.
“Elephants belong to an ancient order of mammals called proboscideans, which first appeared in Africa roughly 60 million years ago as small, nondescript herbivores,” says co-author Steve Salisbury, associate professor at UQ. “In contrast, sauropods – whose ancestors first appeared 230 million years ago – are more closely related to birds. They were agile, two-legged herbivores and it was only later in their evolution that they walked on all fours. Crucially, the transition to becoming the largest land animals to walk the earth seems to have involved the adaptation of a heel pad.”
As technology develops, a lot more palaeontology is being done through scans and computer simulations. This allows scientists to not only look at the fossilised remains of animals which lived tens of millions of years ago, but also make even more discoveries about how they lived.
The 3D-modelling techniques used in the sauropod foot study are applicable to other areas of palaeontological research.
“I’m keen to apply a similar method to an entire limb and to include additional soft tissue such as muscles, which are rarely preserved in fossils,” Jannel says. “We’re also excited to study the limbs and feet of other prehistoric animals. This should allow us to answer different questions about the biomechanics of extinct animals and better understand their environmental adaptations, movement and lifestyle.”