Spinosaurus Was an Aquatic Predator, New Bone Study Shows

For decades, paleontologists have argued about how the massive Spinosaurus lived and hunted. Now, a groundbreaking study on bone density finally settles the debate. By examining the internal structure of dinosaur fossils, scientists have proven that this giant predator was fully adapted to swim and hunt underwater.

The Long Debate Over a Giant Predator

The Spinosaurus is one of the most famous and bizarre dinosaurs ever discovered. It grew up to 50 feet long, weighed around seven tons, and sported a massive sail on its back. It also had a long, narrow snout filled with cone-shaped teeth that looked incredibly similar to a modern crocodile.

Because of its anatomy, scientists always knew the Spinosaurus ate fish. The real argument was about how it caught them. One group of scientists believed the Spinosaurus waded in the shallow water like a giant grizzly bear or a heron, snatching fish from the surface. Another group argued that the Spinosaurus actively pursued its prey deep underwater.

The discovery of a paddle-like tail in 2020 strongly suggested the dinosaur could swim. However, critics argued that its massive body would have been too buoyant to submerge. To solve this puzzle, a team of researchers looked past the shape of the bones and focused entirely on what was inside them.

How Dense Bones Work as Scuba Weights

If you want to understand how an extinct animal moved in the water, you have to look at animals that are alive today. Lead researcher Matteo Fabbri, a postdoctoral researcher at the Field Museum in Chicago, worked with an international team to do exactly that. They published their findings in the journal Nature in March 2022.

The research team analyzed the femur and rib bone cross-sections of 250 different species. This massive dataset included living and extinct animals. They looked at modern marine mammals, flying reptiles, birds, crocodiles, and various dinosaurs.

They were looking for a specific evolutionary adaptation called osteosclerosis. Here is how bone density affects an animal in the water:

• Hollow Bones: Land animals and flying birds have hollow centers in their bones. This keeps them light and agile. If an animal with hollow bones tries to dive, it will naturally float back to the surface.
• Dense Bones: Animals that hunt underwater need ballast. By filling the hollow centers of their bones with solid tissue, they become heavy enough to sink easily. Modern animals like penguins, hippos, and manatees all have incredibly dense bones to help them stay submerged.

When Fabbri and his team put Spinosaurus bones under a CT scanner, the results were undeniable. The bones were completely solid. There was almost no hollow cavity inside the femur. The Spinosaurus had evolved its own internal weight belt, allowing it to sink into the deep rivers of its habitat and actively chase aquatic prey.

Comparing the Spinosaurid Family

The researchers did not stop at the Spinosaurus. They also looked closely at the bone structures of its close relatives to see if the entire family tree shared this aquatic lifestyle. The results revealed a fascinating split in how these dinosaurs evolved.

They tested the bones of Baryonyx, a slightly smaller relative that lived in what is now the United Kingdom. Just like the Spinosaurus, the Baryonyx had highly dense, solid bones. This means it was also an active, underwater swimmer.

However, when they tested a dinosaur called Suchomimus, which lived in modern-day Niger, they found something entirely different. Even though Suchomimus had a crocodile-like snout and ate fish, its bones were hollow. This means Suchomimus lacked the ballast needed to swim underwater. It was an active wader, hunting from the riverbanks exactly like a modern heron.

Life as a Cretaceous River Monster

Understanding this bone density data paints a terrifying and vivid picture of Cretaceous North Africa. Around 95 million years ago, the area known today as the Kem Kem beds in Morocco was a massive, winding river system.

The water was filled with giant aquatic life. The Spinosaurus shared its habitat with Onchopristis, a massive prehistoric sawfish that could grow over 20 feet long. It also swam alongside ancient lungfish and car-sized coelacanths.

To catch these massive fish, the Spinosaurus used its dense bones to submerge without fighting its own buoyancy. It used its powerful, fin-like tail to propel itself through the murky water. Once it caught up to its prey, its interlocking, conical teeth acted as the perfect trap for slippery fish.

This study is a massive leap forward for paleontology. It proves that dinosaurs did not just dominate the land. At least one group of giant theropods successfully conquered the water, living a lifestyle much closer to a giant marine reptile than a traditional dinosaur.

Frequently Asked Questions

Was the Spinosaurus bigger than a T-Rex? Yes, the Spinosaurus is the largest carnivorous dinosaur currently known to science. It reached lengths of up to 50 feet, making it longer than a Tyrannosaurus Rex (which typically grew to about 40 feet). However, the T-Rex was bulkier and likely had a more massive bite force designed for crushing bone.

Did all dinosaurs have hollow bones? Most theropod dinosaurs (the group that includes T-Rex, Velociraptor, and birds) had hollow bones. This adaptation made them lighter and faster on land. The solid bones found in Spinosaurus and Baryonyx are highly unusual for dinosaurs, highlighting their specific adaptation to water.

Could the Spinosaurus walk on land? Yes. While it was highly adapted for swimming, the Spinosaurus was still a dinosaur with strong hind legs. It likely walked on two legs when on land, though it was much slower and more awkward on the riverbanks compared to land-based predators. It probably spent the vast majority of its life in the water.

How did the Spinosaurus breathe underwater? Like modern crocodiles, whales, and hippos, the Spinosaurus was a reptile that breathed air. It did not have gills. It had to hold its breath while submerged. Its nostrils were positioned high up on its snout, allowing it to easily breathe while resting near the surface of the water.