According to Nature, Spinosaurus could have been an underwater hunter like a crocodile or penguin. This is according to a study. For decades, paleontologists have been divided on the habits of this Cretaceous predator that was larger than Tyrannosaurus rex. Some believe it could swim while others think it could not. A team of international researchers now believes it can dive to hunt.

Spinosaurus, also known as the spine lizard, lived between 112 million and 93.5 millions years ago in North Africa. In 1912, the first remains of the species were found in Egypt. Three years later, the German paleontologist Ernst Stromer drew up a description for the new species. These fossils were destroyed in World War II. However, new remains have been discovered in Egypt and Morocco in the 21st century.

The longest land dinosaur was 16 meters in length and weighed 8 tons. Its name derives from its 1.65 meter long vertebral spines. It is thought that they were linked by skin, creating a type of sail. Matteo Fabbri is a researcher at Chicago’s Field Museum of Natural History and the lead author of this study.

The dinosaurs were for a long time the only group of animals that didn’t live in water. The authors point out that the discovery in 2014 of a spinosaur skull, “with conical dentition and retractable nostrils,” shortened hind legs, shovel-shaped feet and a fin-like tail” led to the possibility of an aquatic lifestyle. This was supported by more ambiguous evidence through isotopic analysis. The debate raged between those who believed the animal could swim and those who claimed it was only able to stand in shallow water, sticking its head in it to catch prey.

‘Baryonyx,’ a relative of ‘Spinosaurus,’ with a fish between his jaws. / David Bonadonna

Fabbri admits that “if there are so many different interpretations of the same bones it is a clear indication that maybe these are not the most reliable indicators for us to infer ecology of extinct animal species”. He and his colleagues decided to pursue a different path. “Our study had one goal: It was clear that fossil data can be interpreted in different ways. What about general physical laws? Certain laws are universally applicable to all organisms on the planet. The first refers to water density and submergibility.

The animal’s ability to swim and sink is determined by its bone density. Studies have previously shown that water-adapted mammals have dense, compact bone in their postcranial skulls. Dense bone acts as buoyancy control, allowing the animal to sink. They compared Spinosaurus’ bone density with the femurs, ribs, and other extinct and living aquatic and terrestrial animals to determine if it could swim.

“We include seals and whales, elephants and mice, as well as hummingbirds. There were dinosaurs of all sizes and extinct marine reptiles such as plesiosaurs, mosasaurs, and plesiosaurs. There were animals that weighed several tons, and others that weighed only a few grams. Fabbri says that the dispersion was large. First, there was a strong correlation between underwater foraging and bone density, as well as bone density that is lower – bone with hollow centers – and land animals.

They applied the same paradigm to Spinosaurus and Baryonyx, a distant relative. The density of both bones coincides with submersibility in Spinosaurus, while it does not for ‘Suchomimus, a relative of both. . However, the bones of large herbivorous dinosaurs like long-necked Sauropods have become dense due to their swimming habits. “Heavy animals like elephants, rhinos, and sauropods have dense limb bones due to the high stress they are subject to. Despite this, other bones are relatively light. Fabbri explains that it was crucial to examine a variety bones from all the animals involved in the study.