Spinosaurus didn’t swim after dinner, study claims
Spinosaurus was one of the largest carnivorous dinosaurs and ate fish. Many paleontologists agree on this.
But did he just wade into the rivers and yank them out of the water like a grizzly bear? Or did he dive after his prey like a penguin or a sea lion?
This has become a matter of keen debate among dinosaur experts.
One group is increasingly convinced that Spinosaurus was a rarity among dinosaurs: one that stuck its head underwater and swam beneath the surface. Others say no.
The latest salvopublished Wednesday in the journal PLOS One, comes from the Spinosaurus-couldn’t-swim contingent to counter a pro-swimming article published a few years ago. The previous work, published in the journal Nature, claimed that animals that spend much of their time in the water, such as penguins, tend to have denser bones that provide ballast and make diving easier. Spinosaurus also had dense bones and was therefore most likely a swimmer, the Nature article concluded.
But that bone density analysis was “statistically absurd,” says Nathan Myhrvold, a former Microsoft chief technology officer and amateur paleontologist who led the new study with Paul Sereno, a paleontologist at the University of Chicago.
Dr. Myhrvold and Dr. Sereno have also argued that Spinosaurus’s clumsy body shape would have made it a poor swimmer, if it could swim at all. The dinosaur’s weight distribution would have made it top-heavy and unstable, said Dr. Myhrvold.
“It’s clear why it can’t swim,” he said.
The giant sail on its back would make it difficult for a swimming Spinosaurus to stay upright, said Dr. Myhrvold. “If it tips even the smallest amount, it will keep tipping.”
In other words, the Spinosaurus would capsize and have difficulty pulling its sail out of the water.
There are points of agreement in this dispute. Spinosaurus may have been longer and heavier than Tyrannosaurus rex. It lived about 95 million years ago in what is now Western Sahara, but was then a lush environment with deep-flowing rivers. It was also a strange-looking dinosaur, with elongated vertebrae that formed a huge sail on its back.
Interest in Spinosaurus has increased over the past decade after a new fossil was discovered in Morocco by Nazir Ibrahim, who also authored the earlier bone density study and is now a senior lecturer at the University of Portsmouth in England. The only other fossil was found in 1915 by Ernst Stromer, a German paleontologist, and destroyed during an aerial bombardment of Munich in 1944.
In the latest study, Dr. Myhrvold and colleagues that the paleontologists who made the bone density claims used a sophisticated statistical technique without understanding its limitations.
“It’s being completely misapplied here,” said Dr. Myhrvold. “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 sparked esoteric statistical battles before, criticizing findings on dinosaur growth rates and claiming that a NASA trove of asteroid data is flawed and unreliable.
Previous research by other researchers has shown that diving mammals tend to have denser bones than mammals that stay on land. But other mammals have dense bones for other reasons too. 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 predictor of whether an animal lived in water or on land for a much wider range creatures, including extinct species.
“We thought, oh, are these just mammals and or are these also reptiles?” said dr. Fabbri 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 correlated with the likelihood of going underwater.”
Spinosaurus and a Baryonyx, a relative of Spinosaurus, did dive, while another related dinosaur, Suchomimus, did not, the team of scientists concluded.
Dr. However, Myhrvold argues that bone density cannot be neatly divided into two groups. There are many aquatic animals whose bones are less dense than many land animals, and vice versa. “If the two distributions are close to each other, you can’t draw a valid conclusion, 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. So if someone tells you that a person weighs 135 pounds, you can tell whether that person is a man or a woman.
Although Dr. Myhrvold and Dr. Sereno now disagree with Dr. Fabbri and Dr. Ibrahim, they were once all on the same side as the co-authors of the 2014 article describing the Spinosaurus discovered in Morocco.
Dr. Fabbri is currently in the same department as Dr. Sereno, although he will become a professor at Johns Hopkins University this summer.
“We say hello in this hallway,” said Dr. Fabbri. “It’s okay. Obviously we’re not killing each other.”
Dr. Ibrahim, who is conducting additional studies in Morocco, said further findings would provide even more compelling evidence that Spinosaurus lived in water.
He also rejected the biomechanical arguments of Dr. Myhrvold explains why Spinosaurus couldn’t swim, and said much remains unknown. He compared Dr. Myhrvold’s findings to paleontologists who once argued that tyrannosaurs must have been scavengers because they could not run fast enough to catch small, fast prey. But tyrannosaurs didn’t have to be fast to take down a large, slow-moving triceratops.
Likewise, prehistoric African rivers were filled with giant, slow-moving fish, said Dr. Ibrahim. Spinosaurus didn’t have to be a skilled swimmer to catch them.
“I can’t reveal too much,” he said. “But we have new material. We have some very exciting ongoing projects.”