A dinosaur bigger than T. rex swam and hunted its prey underwater

Bone density can be used as evidence for adaptation to life in water, the study said, as even aquatic animals that are not clearly shaped for an aquatic lifestyle — such as the hippopotamus — have very dense bones.

The researchers found that spinosaurids — a family of predatory dinosaurs that can be up to 15 meters (49 feet) in length (larger than a T. rex) — had dense bones, suggesting they were adapted to life in the water. None of the other 39 dinosaurs the research team investigated as part of the study were likely at ease in water, they said.

Spinosaurids’ relationship with water

Within the spinosaurid family, they concluded that Spinosaurus, which has a distinctive sail-like feature on its spine, and its close relative Baryonyx had increased bone density and would have been able to swim and hunt while submerged underwater — a bit like a crocodile or hippo. Suchomimus, another related dinosaur, had lighter bones that would have made swimming more difficult. It likely lived by water and ate fish, as evidenced by its crocodile-like snout and conical teeth, but based on its bone density, it wasn’t actually swimming, the study found.

“The nostrils of Spinosaurus is not at all placed like it is in animals like hippos and crocs, which spend much of their time submerged; instead, it is placed back on the skull as it is in herons and other animals which feed by dipping their snout in the water to feed,” said Holz, who wasn’t involved in the study.

“The new evidence is consistent with it being able to submerge, at least sometime(s). But as we showed in a paper last year, it couldn’t have been a really fast swimmer with that large sail, at least not in shallow water.”

Jason Poole, an adjunct professor at Drexel University and the Bighorn Basin Paleontological Institute’s director of fossil preparation, said he would have liked to see more specimens related to Spinosaurus included in the study.

“Oddball dinosaurs tend to offer insight into the extremes of dinosaur evolution. The more specimens the better to understand how they got to be so odd,” said Poole, who wasn’t involved in the research.

“I think this study is a good one to keep the ball rolling but more work is always needed to get a better picture of the life of something so strange and far removed in time.”

Big data

The researchers, including scientists from the United States, Europe and Morocco, first compiled a database of sections of thigh bones and rib bones from a variety of animals to understand whether there was a universal correlation between bone density and behavior.

They cast a wide net. “We included seals, whales, elephants, mice, hummingbirds. We have dinosaurs of different sizes, extinct marine reptiles like mosasaurs and plesiosaurs. We have animals that weigh several tons, and animals that are just a few grams. The spread is very big,” Fabbri said.

They found that 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 donuts, with hollow centers.

They did find that other dinosaurs, such as the towering plant-eating sauropods, also had dense leg bones, but other bones were lightweight. Fabbri said this was a pattern also seen in very heavy living land animals like elephants and rhinos.

The research is an example of a big data approach to paleontology that has yielded intriguing insights into how dinosaurs experienced their world — something that is often hard to ascertain from studying fossils of individual animals.

Such studies, according to Jingmai O’Connor, a curator at the Field Museum and co-author of the bone density study, that draw from hundreds of specimens, are “the future of paleontology.”

“They’re very…