Sereno et al. argue Spinosaurus wasn't aquatic

[Newt]

And yet hippo-like morphology is used to argue for semiaquatic habits in a range of extinct mammals (coryphodonts, uintatheres, toxodonts, pyrotheres, astrapotheres, amynodontid and teleoceratin rhinos, early proboscideans, etc.). It goes to show how tenuous some paleontological reasoning is, and how biased it is by the animals we happen to be familiar with. That's why Spinosaurus is so hard to pin down - it is not much like any living animal, and the piecemeal way we compare one part at a time to better-understood animals may not be a good way to determine its lifestyle and capabilities. But the only currently available alternative is to throw our collective hands up and say, "Who knows?"

[bmathison1972]

And yet hippo-like morphology is used to argue for semiaquatic habits in a range of extinct mammals (coryphodonts, uintatheres, toxodonts, pyrotheres, astrapotheres, amynodontid and teleoceratin rhinos, early proboscideans, etc.). It goes to show how tenuous some paleontological reasoning is, and how biased it is by the animals we happen to be familiar with. That's why Spinosaurus is so hard to pin down - it is not much like any living animal, and the piecemeal way we compare one part at a time to better-understood animals may not be a good way to determine its lifestyle and capabilities. But the only currently available alternative is to throw our collective hands up and say, "Who knows?"

Yup

[Bowhead Whale]

True, but what could eat Spinosaurus with that elongated, narrow snout? This kind of snout looks pretty much like this of a gavial to me. So, to me, it did live, if not in water, at least near water. No?

[Newt]

I think everyone agrees that Spinosaurus lived near water and ate fish (and doubtless many other animals as well). Both fish and dinosaur remains have been found in the stomach region of a Baryonyx, the only spinosaurid AFAIK for which there is any direct dietary evidence. Spinosaurus's snout is long and narrow, but proportionately more robust and with relatively larger teeth than a gharial - more like a crocodile in that regard. Gharials are specialists on small fish; crocs certainly do eat small fish, but they are not as specialized as gharials and can also tackle larger fish, turtles, and terrestrial animals.

[stargatedalek]

Spinosaurus however does not have the crushing jaw structure of crocodilians. Seems silly it would be ambushing animals from the water like a crocodile.

A better comparison would probably be aquatic birds like loons or cormorants, or even dolphins. Narrow, but still robust for their size, jaws. These sorts of jaw structures are based around giving an animal extended reach, rather than picking out abnormally small prey like gharial.

[GojiraGuy1954]

Heron Spino has always been an exceedingly stupid idea to me considering the state Spinosaurus' legs are in

[suspsy]

Most of the land animals that coexisted with Spinosaurus were either sauropods or other big theropods, none of which it would have been well-equipped to tackle. Its teeth weren't designed for slashing bites like Carcharodontosaurus' nor were its jaws strong enough to subdue a struggling victim on land. Similarly, Indian gharials are among the very largest extant crocodilians, but even a 20 foot long male isn't capable of killing a human, let alone a cow. So regardless of whether Spinosaurus was a swimmer or a wader or both, its diet would have consisted mainly if not entirely of fish.

[Newt]

@suspy - Don't forget that most or all non-avian dinosaurs were r-strategists - there would have been far more juveniles than adults of any given species in an area. Spinosaurus would probably not have taken on adult Carcharodontosaurus or Paralatitan - that would have been suicidal - but I feel certain it snapped up juvenile dinos as at least a portion of its diet.

@stargatedalek - You are certainly correct that Spinosaurus was not built to tackle prey near its own size the way the biggest Crocodylus species (salties, Niles, Americans) do today. However, most of the smaller Crocodylus species, as well as Tomistoma and Mecistops, feed on moderately-sized land animals as well as fish of various sizes. Also, Spinosaurus' jaws and teeth were more robust than those of Baryonyx, which again is confirmed to have fed on juvenile dinosaurs as well as fish.

@GojiraGuy1954 - Spinosaurus does seem ill-adapted to wading, but it also seems ill-adapted to every other form of locomotion. If it were obvious what it was doing we wouldn't be having this conversation!

It's a bit silly, but I do sometimes wonder if Spinosaurus was an ambush predator that just squatted down in the shallows, using its sail as a shade structure to attract prey and reduce glare (the way some herons use their wings). This scenario would at least not require it to have better ambulatory or natatory powers than its anatomy indicates.

[Sim]

Spinosaurus behaving like a heron isn't as bad an idea as one might think, Spinosaurus had proportionally short legs but given how enormous it was its legs still ended up being huge.  Scaled up for the largest Spinosaurus specimen, the legs would have been taller than an average human!  I think having longer legs wouldn't have been helpful for an animal that size.  The legs of Spinosaurus to me seem the right size for heron-like behaviour.

It's interesting to hear Mecistops also feeds on land animals of that size, I knew Tomistoma did which surprised me when I first found that out given its narrow jaws.  As far as I've seen, Baryonyx had more robust jaws than Spinosaurus and study of their anatomy showed Baryonyx's jaws were better at resisting force than Spinosaurus's were.

I think Spinosaurus using the sail to create shade and reduce glare, thus attracting prey is the most likely way it hunted, though I don't think it needed to squat down, I think standing would put it at the right height.

[stargatedalek]

It could also have used the shade method while floating.

[GiganotosaurusFan]

Good points here.
Spinosaurus did live alongside a lot of other large animals as well, but it would have been one of the largest dinosaurs in its ecosystem. If it didn't live in water and prey on the fist like a modern gharial, it would, because of that sail, be prone to violent and sudden attacks by other carnivores or even packs of them.
Just my honest opinion. Feel free to disagree.

[tinyvinyldinos]

@GojiraGuy1954 - Spinosaurus does seem ill-adapted to wading, but it also seems ill-adapted to every other form of locomotion. If it were obvious what it was doing we wouldn't be having this conversation!

Honestly, I've always been reminded most firmly of an otter skeleton when looking at that leg anatomy. But imagining spinosaurus walking like an otter, with that sail... I don't think that's happening.

[suspsy]

Another interesting detail about this study is that it estimates the weight of Spinosaurus to have been just over 8 tons, confirming it to have been lighter than both Giganotosaurus (8.5 tons) and Tyrannosaurus rex (9-10 tons).

[Bowhead Whale]

Another interesting detail about this study is that it estimates the weight of Spinosaurus to have been just over 8 tons, confirming it to have been lighter than both Giganotosaurus (8.5 tons) and Tyrannosaurus rex (9-10 tons).

Longer and taller animals being lighter or thinner than shorter animals is not uncommon! Look at bowhead whales, for example. They are a lot shorter than the gigantic blue whale, but it has a bigger mouth, longer baleens and, most of all, a much thicker waist than the blue whale. OK, the bue whale is still heavier, but is a whole lot slimmer than the bowhead. So, Spinosaurus being lighter than T-Rex, well, it is not such a big surprise.

[andrewsaurus rex]

well, if Spinosaurus wasn't a swimming animal, then Collecta's new release is in big trouble! 

it's an interesting idea that Spino used its sail for shading, to attract prey.  It would explain the currently accepted shape of roughly rectangular, which would provide more shade than a crescent shaped sail.     So perhaps a shoreline or shallow wading lifestyle would be possible.  Though given the size of the fish that could be reached near the shore and the size of Spino, it would have to eat a LOT every day.  One wonders if the fish wouldn't learn or evolve  to avoid the shallows, where large scale death occurs.

As far as protection from other larger predators, it's possible that Spino lived in colonies of several animals, much as crocodiles do, and the protection of the group kept large predators away, searching for easier game.

Until concrete proof exists, i'm still going to  regard Spino as an animal that swam, decently, and could go deep enough to pursue  good sized fish and other aquatic animals, but spent much of its time sunning on the shore.  The purpose of the sail I am undecided on, although it probably served more than one function eg attract a mate, species recognition, temperature regulation, protection of back from predators, creating shade to lure prey etc.

[Sim]

The shape of Spinosaurus's back sail isn't known, there isn't a "currently accepted" shape.

[andrewsaurus rex]

the 'M' shaped sail for Spino has been around for years now and is portrayed in almost every restoration.  To me that makes it the currently most accepted shape.  I've always said I was skeptical of the shape but it seems to be the most accepted, for whatever reason.   My point was that if it is that shape, it would support the idea of using it to create shade to lure prey.

[Newt]

Fish as big as Spinosaurus could handle frequently enter meter-deep or even shallower water today. I've seen man-sized sharks in such shallows, and smaller (but still substantial enough to be a worthwhile target for a big Spinosaurus) catfish, mullet, drum, rays, gar, carp, and so on in water so shallow they were barely able to fully submerge. The teeming molluscs, crustaceans, and small fish of shallow estuarine shorelines are a powerful lure to predatory fish, even if it brings them within reach of shoreline hunters.

I doubt Cretaceous fish were any different. Even with proportionately short legs, Spinosaurus could easily wade much deeper than a meter. So I don't think a swimming Spinosaurus would necessarily have access to larger fish than a wading Spinosaurus.

I'm not really advocating for a wading lifestyle here; I think the evidence presented so far is pretty ambiguous. I just find the idea of Spinosaurus being an effective swimming predator even more preposterous than the other options. 

[Sim]

A @andrewsaurus, the M shaped Spinosaurus sail has no evidence to support it and is only depicted so often because it's become a palaeoart meme.  Scott Hartman explains this here: https://www.skeletaldrawing.com/home/the-road-to-spinosaurus-ii-known-unknowns11252020

[andrewsaurus rex]

Sim:  I realize the M sail had no evidence, I remember asking on here in my early days as a member where the M shape came from as the fragmentary fossil evidence could suggest almost any shape....however I never got a response.  That link you provided is interesting.   I read that the M shape was inspired by the sailfish......which is weird since sailfish can retract their sail and Spino couldn't.  I'm dubious of the shade idea, I just found it interesting and that  a rectangular sail shape (which the M sorta is) would support the shade idea.

Newt: I agree that Spino was probably not a good swimmer, at least underwater.  I said something to the affect in my early days on here and was promptly shot down  .   But to me that big sail on the back would be a serious impediment to swimming under water.  It would cause lots of drag and make quick maneuvers very difficult, which a fish hunting animal would need to be able to perform.

My best idea for Spino is that it swam along the surface, perhaps for hours at a time, lunging at fish below it when opportunity presented.  The sail could have been used to keep Spino warm, during long hours of swimming, as water is a very effective heat sink and the animal may have gotten chilled during long periods in the water.  However this idea  has been shot down on here too.