Bones suggest the largest carnivorous dinosaur was a good swimmer

Clarity at last: Spinosaurus was probably excellent at hunting ill-fated prey underwater.

the terrifying spinosaurus is the largest carnivorous dinosaur ever discovered – it was even bigger than the famed T. rex! The way in which spinosaurus however, has been the subject of debate for decades. Some scientists assume that spinosaurus could swim, while others believe he waded through the water like a heron. However, a new analysis of his bones puts an end to the ongoing debate.

water dwellers

All life originates from the water. And some land animals have also returned to the water. While most mammals are land dwellers, whales and seals live in the ocean. Some other mammals, such as otters and hippos, are ‘semi-aquatic’. Birds include penguins and cormorants, while reptiles include crocodiles, marine iguanas and sea snakes. For a long time, however, the so-called “non-avian dinosaurs”—the dinosaurs that didn’t branch out into birds—were the only group that didn’t have aquatic inhabitants. That changed in 2014, when a new Spinosaurus skeleton was discovered.

It soon became clear that spinosaurus was a real water rat. It had elongated, crocodile-like jaws and cone-shaped teeth similar to those of other aquatic predators. In addition, some fossil specimens with a belly full of fish have been found. However, it remained unclear whether spinosaurus was a swimming river monster, or just standing in the shallows and poking its head under the water every now and then to startle an unsuspecting little fish swimming by. It is not surprising that this remained doubtful. The behavior of an animal known only from fossils is difficult to guess. “In addition, there are only a handful of partial skeletons of spinosaurs discovered,” said researcher Matteo Fabbri.

Bones

Because studying the anatomy of spinosaurus apparently not enough to solve the mystery, researchers have taken a different tack in a new study. In the study, they analyzed the density of the bones. Bone density reveals whether an animal in question is capable of swimming. “Previous studies have shown that aquatic mammals have dense and compact bones,” Fabbri said. “This gives an animal control over its buoyancy and can ‘submerge’ itself.”

This image shows the bone density per animal. Aquatic animals have more solid bones, while land dwellers often have hollow bones. Image: Fabbri et al.

The researchers collected cross-sections of the femur and ribs from 250 species of extinct and living animals — both terrestrial and aquatic. They then compared these cross-sections with the bones of spinosaurus and his relatives Baryonyx and suchomimus†

good swimmer

It leads to an interesting discovery. Because the bone density of spinosaurus betrays that he must have been a good swimmer. Its almost completely solid bones allowed it to hunt fatal prey under water. Also his closest relatives Baryonyx was a great swimmer. On the other hand, suchomimus about hollow bones. This means that this dinosaur did spend a lot of time in the water eating fish, as its crocodile-like snout and cone-shaped teeth suggest. But based on his bone density, the researchers hypothesize that he probably waded through water similar to a heron.

The study reinforces the assumption that swimming dinosaurs really existed. In addition, Fabbri notes that the study shows how much information you can extract from partially preserved fossil skeletons. And that creates hope for future discoveries. “Even if you only have a few bones from a newly discovered dinosaur, you can still compile a dataset to calculate bone density,” he says. “And from that you can at least deduce whether the beast lived in the water or not.”