The study claims that Spinosaurus did not swim after dinner

Spinosaurus was one of the largest carnivorous dinosaurs, and it ate fish. This is what paleontologists often agree on.

But did he wade into rivers and snatch them from the water like a grizzly bear? Or did it dive after its prey like a penguin or sea lion?

This has become a matter of contentious contention among dinosaur experts.

One group is increasingly convinced that Spinosaurus was rare among dinosaurs: it stuck its head underwater and swam below the surface. Others say no way.

Latest shotspublished Wednesday in the journal PLOS One, comes from the Spinosaurus that couldn't swim team to counter a pro-swimming paper published two years ago. Previous work, published in the journal Nature, He claimed that in general, animals that spend most of their time in the water, such as penguins, have denser bones that provide heaviness and facilitate diving. The Nature paper concluded that Spinosaurus also had dense bones and was therefore likely a swimmer.

But the bone density analysis was “statistically ridiculous,” said Nathan Myhrvold, a former chief technology officer at Microsoft and an amateur paleontologist who led the new research with Paul Sereno, a paleontologist at the University of Chicago.

Dr. Myhrvold and Dr. Sereno also argued that Spinosaurus's inappropriate body shape would have made it a poor swimmer, if it could swim at all. Dr. Myhrvold said the dinosaur's weight distribution would have made it very heavy and unstable.

“It's obvious why he can't swim,” he said.

The giant sail on its back would have made it difficult for a swimming Spinosaurus to stay upright, Dr. Myhrvold said. “If you tip even the smallest amount, you will continue to tip.”

In other words, the Spinosaurus would capsize and struggle to pull its sail out of the water.

In this disagreement, there are points of agreement. Spinosaurus was probably longer and heavier than Tyrannosaurus rex. It lived about 95 million years ago in what is now Western Sahara, but it was then a fertile environment with deep-flowing rivers. It was also a strange-looking dinosaur, with its long vertebrae forming a huge sail on its back.

There has been significant interest in Spinosaurus in the past decade following the discovery of a new fossil in Morocco by Nizar Ibrahim, who was also the author of an earlier study on bone density and is now a senior lecturer at the University of Portsmouth in England. The only other fossil was found by Ernst Stromer, a German paleontologist, in 1915, and was destroyed in an aerial bombing of Munich in 1944.

In the latest study, Dr. Myhrvold and his colleagues say that paleontologists who made bone density claims used a sophisticated statistical technique without understanding its limitations.

“This has been completely misapplied here,” Dr. Myhrvold said. “Unfortunately, when you have something that involves a lot of dense statistics, most paleontologists' eyes glaze over.”

Dr. Myhrvold is not a traditional academic. Since leaving Microsoft in 1999, he is perhaps best known for leading the development of the encyclopedic Modernist Cuisine cookbooks. But he has previously sparked esoteric statistical ruckus, criticizing findings about dinosaur growth rates and claiming that NASA data on asteroids is flawed and unreliable.

Previous work by other researchers has found that diving mammals tend to have denser bones than mammals that remain on land. But other mammals also have dense bones for other reasons. Elephants, for example, need stronger bones to support their weight.

In 2022, researchers led by Matteo Fabbri, now a postdoctoral researcher at the University of Chicago, argued in their paper that bone density was a reliable indicator of whether an animal lived in water or on land for a much broader range of creatures, including Extinct species.

“We thought, 'Oh, are these just mammals or are they reptiles too?' Dr. Fabbri said in an interview. “And if this is true, can we infer the ecology of extinct animals, including strange-looking dinosaurs like Spinosaurus?”

Dr Fabbri said the analysis showed that “very high bone density is associated with the likelihood of going underwater”.

The team of scientists concluded that Spinosaurus and Baryonyx, a relative of Spinosaurus, did dive, while another related dinosaur, Saucomymus, did not dive underwater.

However, Dr. Myhrvold believes that bone density is not strictly divided into two groups. There are many aquatic animals with less dense bones than many terrestrial animals and vice versa. “If the two distributions are close to each other, you won't be able to get a correct result, or at least one that has any statistical power,” he said.

He gives an example: In humans, men are generally heavier than women, but not every man is heavier than every woman. Therefore, if someone tells you that someone weighs 135 pounds, you will not be able to reliably conclude whether that person is male or female.

Although Dr. Myhrvold and Dr. Sereno are now at odds with Dr. Fabbri and Dr. Ibrahim, they were all on the same side as the co-authors of A 2014 paper that described Spinosaurus was uncovered in Morocco.

“We were divided intellectually,” Dr. Sereno said.

Dr. Fabbri currently works in the same department as Dr. Serino, although he will become a professor at Johns Hopkins University this summer.

“We say hello in this hallway,” Dr. Fabray said. “It's okay. We're obviously not killing each other.”

Dr Ibrahim, who is in Morocco to conduct additional studies, said further findings would provide a more convincing argument that Spinosaurus was aquatic.

He also rejected Dr. Myhrvold's biomechanical arguments as to why Spinosaurus could not swim, saying much was still unknown. He compared Dr. Myhrvold's findings with paleontologists who argued that tyrannosaurs must have been scavengers because they were unable to run fast enough to catch small, fast prey. But tyrannosaurs didn't have to be fast to pull off a large, slow-moving Triceratops.

Likewise, prehistoric African rivers were full of giant, slow-moving fish, Dr. Ibrahim said. Spinosaurus didn't have to be a strong swimmer to catch them.

“I can't reveal much,” he said. “But we have new material. We have several ongoing projects that are very exciting.”