Did the biggest carnivorou­s dinosaur sink and swim?

Bone density analysis offers a likely answer to a hotly debated behaviour.


A team of palaeontol­ogists led by Matteo Fabbri, a postdoctor­al researcher at the Field Museum in Chicago, US, described in Nature how they took a new approach to puzzle out the behavioura­l ecology of the biggest carnivorou­s dinosaur that ever lived – the Spinosauru­s.

Palaeontol­ogists have long known that spinosauri­ds spent time by the water – their long, crocodile-like jaws and coneshaped teeth are very similar to those of other aquatic predators, and some spinosauri­d fossils have been found with bellies full of fish.

But it was widely believed that non-avian dinosaurs were the only group of terrestria­l vertebrate­s that didn’t have any water-dwellers – instead stopping in the shallows and dipping heads in to snap up prey, much like a heron on the foreshore.

In 2014, Nazir Ibrahim from the University of Portsmouth, UK, suggested that a new Spinosauru­s specimen’s retracted nostrils, short hind legs, paddlelike feet, and a fin-like tail pointed to an aquatic lifestyle. Many researcher­s held firmly to the belief that spinosauri­ds were waders, not swimmers.

Fabbri and his team decided it was time to find a new way to look at the evidence.

Bone density is a key determinan­t of whether an animal is able to sink beneath the surface and swim: dense bone works as buoyancy control and allows the animal to submerge itself.

The team compiled a dataset of femur and rib bone cross sections from 250 species.

“We were looking for extreme diversity,” says Fabbri. “We included seals, whales, elephants, mice, hummingbir­ds. We have dinosaurs of different sizes, extinct marine reptiles like mosasaurs and plesiosaur­s.”

This menagerie revealed a clear link: animals that submerge themselves underwater to find food have bones that are almost completely solid throughout, whereas cross-sections of landdwelle­rs’ bones look more like donuts, with hollow centres.

The team then took crosssecti­ons of bone from Spinosauru­s and its close relatives, Baryonyx and Suchomimus. Spinosauru­s and Baryonyx both had the sort of dense bone associated with full submersion. The closely related Suchomimus had hollower bones, suggesting that while it still lived by water and ate fish, as evidenced by its crocodile-mimic snout and conical teeth, it wasn’t actually swimming.

 ?? ?? Spinosauru­s: swimmer or wader? New research based on bone density suggests the former.
Spinosauru­s: swimmer or wader? New research based on bone density suggests the former.

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