How the giant sail-backed dinosaur, Spinosaurus, hunted its prey has been a long-standing controversy. Scientists have been debating whether the creature dove deep down to catch its prey or dwelled in shallow waters near the shore.

Water Habits of Giant Spinosaurus

Generally, paleontologists agree that the seven-ton giant Spinosaurus was a fish-eater. However, how the dinosaur lived and preyed on fish has been a long-standing debate subject.

For one, there is research that suggests that the creature swam or waded in shallow waters near the shore to search for its prey. There have also been other studies that hinted that they dove into great depths to catch their meals.

The authors note in the study that, unlike other carnivorous dinosaurs, there are significant clues that hint that the creature lived close to water and consumed fish and other marine fare. This has bolstered the controversy regarding how these dinosaurs lived.

To shed light on the matter, the authors of the new "Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle" study performed an analysis wherein they re-examined the dinosaur's bone density to know more about the creature's life habits in water.

As part of the study, the researchers also noted another 2022 study that supported the hypothesis of aquatic pursuit predation. The researchers examined the argument and concluded that the hypothesis has grave flaws.

Nathan Myhrvold, one of the study authors, explains that the earlier study's gist is that they wanted to make use of bone density and a new statistical analysis to show that the creature was a forager in underwater environments. Myhrvold adds that they revealed that the data used was not appropriate as it did not have the needed characteristics.

Myhrvold and colleagues also say that the hypothesis is not biologically feasible. Though several modern marine mammals have evolved bones that are denser than normal to serve as a ballast and aid them with underwater life, several dinosaurs, such as the Spinosaurus, had air sacs in their spinal bones. Myhrvold explains that the density of the rib and thigh bones does not reveal whether the dinosaur could dive.

The author also noted in an earlier 2022 paper they published that the air sacs of the Spinosaurus offered such buoyancy that the dinosaur could not dive.

While the new study does not settle the long-standing debate about the dinosaur's lifestyle, Myhrvold shares that their key finding is that the 2022 paper incorrectly states that their analysis proves that the Spinosaurus was an underwater hunter.

Findings also suggest that the dinosaur was not a diving or swimming predator that chased fish in a similar manner as a sea lion.

Paul Sereno, another author of the study, shares that they have no bone density evidence that suggests that the dinosaur is not anything else compared to what they judged from other evidence lines in earlier research. This points to the dinosaur being a fish-eating and semiaquatic predator that haunted shallow water and shorelines and ambushed different-sized prey.

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Findings Disputed

However, the findings have been disputed by the team of Fabbri, who was behind the 2022 study. Fabbri shares that they do not think that the data of the new researchers supports their conclusions.

Fabbri notes that, for one, high bone density is observed across the entire Spinosaurus skeleton. Fabbri explains that while the 2024 researchers suggest that only the legs have high bone density, this is not the case. The team of Fabbri was able to observe high bone density in the spines of the rail and sail, ribs, and even hand-forming bones. He explains that animals that adapt to diving underwater exhibit high bone density all over their skeletons.

The researcher also explains that the model used by his team is accurate. He shares that their model is based on modern species' training data set.

Fabbri also adds that the most complete Spinosaurus specimen found lacks bones for the body part where the air sacs would be present: the neck. This could lead to interpretation problems.

He explains that the skeleton can suggest the location of the air sacs, but there are no traces regarding actual volume. Hence, air sac quantification could be overstated easily.

Fabbri notes that, resultantly, the body density estimations that the authors published are lower than the known density of chickens today, which are marked by bones that are hollow. Considering the high bone density observed all over the Spinosaurus' skeleton, this is not possible.

He adds that a morphological feature's presence may not exclude ecological behaviors.

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