Dinosaur paleontology has, historically,聽 been built on disagreement.

We had Othniel Charles Marsh and Edward Drinker聽聽 Cope duking it out in the聽 Bone Wars of the late 1800s.

More like "The Bonehead Wars,"聽 those guys were such jerks.

Then we got Luis and Walter Alvarez dropping聽 their asteroid impact hypothesis into the聽聽 debate about the extinction at the聽 end of the Cretaceous Period in 1980.

And now we have, literally,聽 how wet did Spinosaurus get?

While it’s definitely a more niche  disagreement than those famous聽聽 fossil beefs, it points to something聽 fundamental to the process of science:聽聽 how evidence does – or does not –  stack up to support a hypothesis.

So initially, Spinosaurus was thought聽 to be basically a T.rex with a sail.

But over the last century-ish, it's聽 undergone a radical transformation聽聽 as scientists realized it was聽 probably not just living on land.

Instead, it was likely spending its time聽 around water, making it semi-aquatic.

And that’s where disagreement comes into the   picture – and where our old  Spinosaurus episode left off.

What does it mean to be a “semi-aquatic” dinosaur?

Like, was it wading around in the shallows, like聽 a heron or a crane?

Or could it have actually been聽聽 a skilled swimmer, gliding through the聽 water like a crocodile or an otter?

Each scenario paints a very聽 different picture of Spinosaurus,聽聽 shaping everything from how it聽 moved to how it caught prey.

And the discovery of new fossils聽 has paleontologists rethinking聽聽 just how weird and watery this聽 dinosaur was, all over again.

Ever since Spinosaurus was first named聽 in 1915, it’s been a bit of a mystery.

The few fossils that paleontologist Ernst Stromer聽 had to go on painted the picture of a weird,聽聽 carnivorous dinosaur that looked kind聽 of like T. rex, but also kind of not.

It was huge, with some estimates suggesting up to聽聽 15 meters long – making it one of  the biggest carnivores ever found.

But this giant of the Cretaceous聽 Period was also…different.

The skull of Spinosaurus, for example,聽聽 was long and crocodile-like聽 compared to most large theropods.

And overall, it was just an awkward creature that聽 no one could fully make sense of.

And it didn’t   help that the early fossils Stromer described were聽 lost during the Allied bombings of Munich in 1944.

So for a period, Spinosaurus was聽 kind of an enigma, lost to time.

But then, beginning in the 1980s,聽 other pieces of the puzzle started聽聽 to fall into place when fossils of聽 its close relatives were uncovered.

Like Baryonyx walkeri, found in the UK,聽聽 followed by fragments of other聽 spinosaurids throughout North Africa.

These new fossils suggested that spinosaurids had聽 convergently evolved similar traits to crocodiles.

And the researchers that worked on聽 them concluded that, like crocodiles,聽聽 spinosaurids must have been eating fish.

In 1997, this idea gained more support聽 when fish scales were found during聽聽 the re-analysis of the stomach聽 contents of a Baryonyx specimen.

Then, in the early 2000s, scientists聽 turned their attention to using stable聽聽 isotopes to infer the diet and聽 ecology of spinosaurs in general.

An isotope is a version of an element that has聽 a different number of neutrons in its nucleus.

And isotopes get incorporated into an animal’s  bones and teeth through its diet, and the ratios聽聽 of different isotopes can help researchers figure聽 out what an animal was eating and drinking.

Basically, you are what you聽 eat, elementally speaking.

Looking at oxygen isotopes from spinosaur聽 fossils, paleontologists discovered that聽聽 these animals had chemical signatures more similar聽 to crocodiles and turtles than other theropods.

And a later study using calcium isotopes from聽 carnivorous dinosaurs in North Africa found聽聽 evidence that spinosaurs like Suchomimus聽 were feeding in aquatic environments,聽聽 while other big theropods聽 stuck to terrestrial ones.

The picture these close relatives聽 painted was that the spinosaurids聽聽 were kind of like 'mega-herons' that waded in聽 the shallows along riverbanks and ate fish.

Extreme emphasis here on聽 the ‘mega’.

Given its size,   Spinosaurus has occasionally聽 been called a ‘heron from hell.’ But that was hardly the end of the debate.

See, there still weren’t a ton of fossils,  especially not of Spinosaurus – and   the fossils that scientists did聽 have weren’t all that complete.

So, when in 2014, a team of paleontologists聽 led by Nizar Ibrahim published new Spinosaurus聽聽 fossils found in rocks in Morocco called聽 the Kem Kem Group, it was a big deal.

Dating to the Late Cretaceous,聽 around 97 million years ago,聽聽 these new finds included pieces of the skull,聽 vertebrae, pelvis, and limbs of a young adult.

And these fossils seemed to suggest to聽 the team that Spinosaurus was spending聽聽 more time in the water than previously imagined.

For instance, its skull had a series of tiny聽 pits that lined the front of the snout, much聽聽 like those seen in crocodiles, which are pressure聽 receptors that detect movement in the water.

And both its nostrils and eyes appeared to聽 be positioned higher than most theropods,聽聽 which would have allowed it to breathe聽 while partially submerged, the team argued.

This hinted at an animal that was not just聽 a riverside hunter, but was actually a聽聽 skilled swimmer, snaring fish while moving聽 through the water like an otter or a croc.

The back half of its skeleton聽 seemed to confirm this, too… Spinosaurus’ hindlimbs and pelvis  were smaller than expected,聽聽 featuring a proportionally short femur.

A shorter femur, Ibrahim’s team  pointed out, is a feature we see聽聽 in living swimming mammals that聽 use their hindlimbs for paddling.

The researchers even thought that聽 Spinosaurus’ feet were potentially webbed,   which would have also benefited an animal聽 hunting fish in North Africa’s river system.

But not everyone was convinced聽 that Spinosaurus was doing more聽聽 than just splashing around in the shallows.

Some scientists argued that the nostril聽 position still would have required the聽聽 animal to raise much of its head above聽 the water to breathe, for example.

Others declared that Spinosaurus’ body  shape suggested it was “unsinkable”   and therefore couldn’t dive to chase fish.

But then, in 2020, Ibrahim and聽 a team of researchers announced聽聽 they had discovered the tail of聽 that same Spinosaurus individual.

The tail was estimated to be about 80% complete,聽 and it was entirely different from what people聽聽 had expected, because it was unlike the聽 tail from any other theropod dinosaur.

Previously, paleontologists had assumed that聽 the tail of Spinosaurus was thick, muscular,聽聽 stiff, and a good counterbalance聽 – like its close relatives.

But this tail had odd features that gave聽 it an almost paddle-like appearance,聽聽 like elongated neural spines.

It was also very long, and it聽 didn’t have features that would   generally stiffen and stabilize it,聽 meaning it had a ton of flexibility.

And all of these traits would be beneficial to聽聽 a swimmer that propelled itself聽 through the water with its tail.

So Ibrahim’s team created models that  compared two terrestrial theropod聽聽 dinosaurs and two aquatic tetrapods聽 – a crocodile and a newt – to show   that the shape of the tail generated聽 enough thrust for an active swimmer.

They concluded that Spinosaurus聽 wasn’t just a wading dinosaur,   but instead a swimmer that pursued its聽 prey in deeper waters – like a crocodile.

So under this hypothesis, the dinosaur would聽 actively dive into rivers, swimming in the聽聽 water to chase lungfishes, coelacanths,聽 and other fish found in the Kem Kem group.

So that’s it, right?

One complete tail and the  arc of the wild Spinosaurus saga is complete?

No, that's actually not what happened...

The idea of a submerged, swimming聽 dinosaur hasn't been universally accepted.

Other paleontologists stuck with the聽 original hypothesis.

For these researchers,聽聽 the animal’s anatomy didn’t  point to an efficient swimmer… Like, those toe claws that had been interpreted聽 as potentially webbed – maybe they weren't   actually that different from the claws聽 of other terrestrial theropods after all.

Then, in 2022, a team working with聽 Ibrahim turned to Spinosaurus’ bone   structure as another way to聽 test the swimming hypothesis.

They looked at bone density, which聽 can vary across species depending聽聽 on how much buoyancy an animal聽 needs when diving or foraging.

And they found a strong correlation between聽 foraging underwater and bone density:聽聽 species who moved underwater to feed聽 had denser bones than those who did not.

And Spinosaurus seemed to have this type of dense聽聽 bone, suggesting that it was聽 likely an underwater forager.

In comparison, another spinosaurid relative聽 from North Africa, Suchomimus, had much less聽聽 dense bones and was, therefore, probably more聽 terrestrial and confined to the water’s edge.

This, of course, has not been the聽 last word on Spinosaurus’ lifestyle… Now look, we could keep citing studies back聽 and forth, like some kind of paleontological聽聽 ping-pong match, with each side聽 of the debate either presenting聽聽 new evidence for their hypothesis or聽 disputing the claims of the other.

Like, we've all seen that movie before, right?

But, ultimately, without聽 more fossils or new methods,聽聽 we’re unlikely to solve  the mystery of Spinosaurus… Which is unsatisfying, I know,聽 I get it, I'm there with you,聽聽 but that’s just what being in the middle  of the process of science is like!

It seems that most researchers now聽 agree that Spinosaurus was some聽聽 version of ‘semi-aquatic’...but there’s a lot of  disagreement about what, exactly, that term means.

What’s really exciting is that its  adaptations show that dinosaurs聽聽 radiated into many niches during the Mesozoic聽 Era, including at least to the waters’ edge.

And these are niches that their聽 descendants, aka birds, still occupy today.

So, whether you think the evidence supports聽 Spinosaurus as a wader or a swimmer,聽聽 the next time you watch a heron聽 spear a fish in your local pond,聽聽