The Spinosaurus is the largest predatory dinosaur known — over two metres longer than the longest Tyrannosaurus rex — but the way it hunted has been a subject of debate for decades.
In a new paper published recently in Nature scientific journal, a group of palaeontologists took a different approach to decipher the lifestyle of long-extinct creatures by examining the density of their bones.
By analysing the density of Spinosaurid bones and comparing them to other animals like penguins, hippos, and alligators, the team found that Spinosaurus and its close relative, the Baryonyx, from the Cretaceous of the UK both had dense bones that would have allowed them to submerge themselves underwater to hunt.
Scientists already knew that Spinosaurids had certain affinities with water, as their elongated jaws and cone-shaped teeth are similar to those of fish-eating predators, and the ribcage of the Baryonyx from Surrey even contained half-digested fish scales.
In the last decade, the University of Portsmouth’s Palaeontologist and National Geographic Explorer Nizar Ibrahim unearthed different parts of a Spinosaurus skeleton in North Africa’s Sahara Desert. The skeleton Ibrahim and his team described had retracted nostrils, short hind legs, paddle-like feet, and a fin-like tail — all signs that firmly pointed to an aquatic lifestyle.
“We battled sandstorms, flooding, snakes, scorpions, and more to excavate the most enigmatic dinosaur in the world, and now we have multiple lines of evidence all pointing in the same direction — the skeleton really has ‘water-loving dinosaur’ written all over it!” said Ibrahim.
Based on its highly specialised anatomy, Ibrahim and his team previously suggested that the Spinosaurus could swim and actively pursue prey in the water, but others claimed that it was not much of a swimmer and instead waded in the water like a giant heron.
Researchers have continued to debate whether Spinosaurus spent much of its time submerged, pursuing prey in the water, or if it just stood in the shallows and dipped its jaws in to snap up prey.
“In part, this is probably because we were challenging decade-old dogma, so even if you have a very strong case, you kind of expect a certain degree of pushback,” Ibrahim added.
The team assembled a very large dataset of femur and rib bone cross-sections from 250 species of extinct and living animals — including both land-dwellers and water-dwellers — of various weights and sizes, including seals, whales, elephants, mice, and even hummingbirds.
The scientists found a clear link between bone density and aquatic foraging behaviour; animals that submerge themselves underwater to find food have bones that are almost completely solid throughout, whereas cross-sections of land-dwellers’ bones look more like doughnuts, with hollow centres.
