Spinosaurus's dense bones may have helped it submerge in water as an aquatic predator. That’s the takeaway from a recent paper that adds to the ongoing debate about these dinosaurs’ lifestyles by comparing features of Spinosaurus’s skeleton to those of other animals.

Yes, it’s another episode of Spinosaurus: Aquatic Or Not? We’re your hosts, IFLScience, and today we’re exploring a paper published in Nature that suggests bone density may be a key indicator as to how the largest predatory dinosaur known to science spent its days.

A pivotal discovery, led by University of Portsmouth paleontologist and National Geographic Explorer Dr Nizar Ibrahim, first invigorated the discussion as his team uncovered fossilized clues pointing to an aquatic lifestyle for Spinosaurus. These included paddle-like feet, a fin-like tail, and short hind limbs – all features that painted Spinosaurus as a “water-loving dinosaur,” said Ibrahim.

But did Spinosaurus pursue prey in the water? Or did it merely wade like a giant stork snatching food from the water? (FYI, some of its close relatives were named "Crocodile-Faced Hell Herons")

Dr Matteo Fabbri of the Field Museum, Chicago, teamed up with Ibrahim to try a new approach to pinning down Spinosaurus’s way of life, looking to its skeletal system as an indicator of its lifestyle and ecology.

“The idea for our study was, okay, clearly we can interpret the fossil data in different ways. But what about the general physical laws?” Fabbri said in a statement. “There are certain laws that are applicable to any organism on this planet. One of these laws regards density and the capability of submerging into water.”

For aquatic hunters to submerge in water, they need dense, compact bone as this contributes to the animals’ buoyancy control.

With the help of an international team of researchers, Fabbri and Ibrahim gathered data on the femur and rib bones of 250 species of extinct and living animals to compare against Spinosaurus and its relatives, Baryonyx and Suchomimus.

The results showed a clear association between lifestyle and skeletal phenotype, with animals known to practice aquatic foraging behaviors found to exhibit higher bone density.

Both Spinosaurus and Baryonyx’s near-solid bones were found to be most like those of animals that hunt or forage in the water, pointing towards these dinosaurs fully submerging themselves in aquatic habitats rather than wading through them.

Suchomimus, on the other hand, had hollow bones that the analyses revealed are more like those of land-dwelling animals. Unexpected, but not necessarily surprising it seems, as other groups of closely related animals were also found to differ in this way.

"The bones don’t lie, and now we know that even the internal architecture of the bones is entirely consistent with our interpretation of this animal as a giant predator hunting fish in vast rivers, using its paddle-like tail for propulsion,” said Ibrahim.

“I think that, with this additional line of evidence, speculative notions that envisage Spinosaurus as some sort of giant wader lack evidential support and can be safely excluded."

When ripples of a paleontological embargo begin to spread across Twitter, dinosaur fans have learned to expect that something Spinosaurus is afoot. The frequency of debates surrounding this ancient beast has meant that in recent months, when news arrives of T. rex being three species instead of one, people were surprised we weren’t talking about Spinosaurus for once.

The aquatic cat on this latest embargo is now out of the bag, but we’d be lying if we said we weren’t a little disappointed that some alternative predictions didn’t turn out to be true.