How this giant dinosaur dubbed ‘heron from hell’ caught its prey

By Stephen Beech via SWNS

A giant dinosaur was the “heron from hell” - snatching its favorite fish from the shallows, according to new research.

The study by American paleontologists uncovered "major issues" with earlier suggestions that the sail-backed mega-predator Spinosaurus pursued its prey underwater.

For years, controversy has swirled around how the Cretaceous-era, sail-backed killer hunted its favorite prey of fresh fish.

Spinosaurus was among the largest predators ever to prowl the Earth and one of the most adapted to water.

But it had remained unclear until now whether it was an aquatic denizen of the seas, diving deep to chase down its meals, or a semi-aquatic wader that snatched prey from shallow water close to shore.

The new analysis, led by University of Chicago scientists, re-examined the density of its bones as a way of determining its life habits in water.

When detailed descriptions of a nearly complete specimen of Spinosaurus were first published in the journal Science in 2014, the Chicago-led research team pitched it as a shoreline stalking or surface swimming demon, not a fully aquatic underwater predator.

But in 2020 an international group of researchers countered that description with a study, published in the journal Nature, using its newly discovered, tall-spined tail bones to suggest that it propelled itself like an eel to hunt underwater.

A 2022 Nature study by many of the same authors confirmed their 2020 assessment showing that Spinosaurus had dense bones to use as ballast in diving like a penguin.

They also argued that some other spinosaurids, such as its older African cousin Suchomimus, had less dense bones and were likely waders.

About the same time in 2022, a group of paleontologists at the University of Chicago teamed up with colleagues elsewhere to test those ideas by creating digital skeletons and flesh models of the Spinosaurus and Suchomimus.

Their findings, published in the journal eLife, found that both species would have been unstable when swimming at the surface and far too buoyant to dive and fully submerge.

Now that same team has taken on the question of bone density, with the findings published in the journal PLOS One.

Senior author Professor Paul Sereno, who co-led the initial discovery of the new Spinosaurus specimen in 2014, said: “We had made the thin sections of these species that were used for bone density calculations, and so we thought we would start by trying to replicate their measurements.

“But we encountered many factors that generated a range of values - enough to undermine the conclusions.”

The team began by asking new questions about bone density, such as how to digitize thin sections, where to slice through the thigh and rib bones, and whether to include bones from more than one individual.

The research team explained that some modern aquatic mammals - such as manatees - have swollen, dense bones to help them stay underwater, like a scuba diver’s weight belt.

Large land animals, such as elephants and dinosaurs, also have dense bones to support their increased body mass.

Most modern birds and many dinosaurs including Spinosaurus have the opposite condition, with air sacs attached to lungs or inside bones that act like a life vest preventing submergence.

The researchers said that assessing the aquatic abilities of an extinct species such as Spinosaurus needs to take account of all those factors.

Given the complexity of understanding the meaning of bone density, Prof. Sereno and his colleagues worked with first author Dr. Nathan Myhrvold, founder and CEO of Intellectual Ventures, to reevaluate how the statistical technique used in the 2022 Nature study was applied to support the claim that Spinosaurus was a deep diver.

They explained that the approach - known as phylogenetic flexible discriminant analysis (pFDA) - is like machine-learning: the pFDA technique trains a classification algorithm on a group of species whose lifestyle is well understood.

In principle, researchers could then use the algorithm to estimate the likelihood that a poorly understood species such as Spinosaurus falls into one behavioral group or another.

However, in practice, Dr. Myhrvold says there are problems that must be overcome.

He said: “Unfortunately, that technique does not work properly unless you have lots of data, you make apples-to-apples comparisons, and you check that the data meet certain statistical prerequisites.

“None of those requirements were met in that earlier study, so the results just didn’t hold up under re-examination.”

The Chicago team say their latest findings also show the importance of taking measurement errors and individual variations into account when assessing bone density.

Prof. Sereno said: “We think Spinosaurus, one of the largest predatory animals ever to have evolved, needed extra bone strength to support its weight on its relatively short hind limbs."

He added: “Spinosaurus was able to wade into waterways more than six feet deep without floating, where it could ambush fish of any size with its claws and jaws - but all while keeping its toes firmly anchored in the mud.”