Sereno et al. argue Spinosaurus wasn't aquatic

[Sim]

There's a new preprint out where Sereno and colleagues argue Spinosaurus was a bipedal semi-aquatic dinosaur that wasn't a good swimmer or diver, based on re-analysis of the bones and new Spinosaurus remains that were found preserved in an inland environment.

I found it interesting and it seems to be based on good arguments.  They propose a different function for the tail (display), and interestingly their skeletals for Suchomimus and Spinosaurus don't have a dip in their spines.

Link to the paper: https://www.biorxiv.org/content/10.1101/2022.05.25.493395v1.full

[Gothmog the Baryonyx]

If someone invents a time machine, straight to Spinosaurus we should go. The palaeontology journey goes ever on in the meantime.

[Sim]

Heh, yes, it would be very satisfying to see what Spinosaurus was really like.

Below is the new skeletals for Spinosaurus and Suchomimus, from the paper:



Suchomimus should really be made into a figure more often, it's the most completely known spinosaurid.

[Concavenator]

interestingly their skeletals for Suchomimus and Spinosaurus don't have a dip in their spines.

Please correct me if I'm wrong, but AFAIK Suchomimus was never thought to have a dip in its sail (like Ichthyovenator)? And there's controversy regarding the actual shape of Spinosaurus' sail. After the 2014 discoveries and I don't know why, the M shape became popular, but as of right now, my understanding is that both the M shape and the round shape are equally right.

[stargatedalek]

And yet this conflicts with the isotope data, which indicates Spinosaurus' body has below water most of its life, while the head above.

Even if the tail wasn't for propulsion, and even if it was a bad swimmer and diver, there's no way "around" that. Spinosaurus spent essentially its entire life in some water, doing something. Perhaps it didn't need to be a strong swimmer but floated calmly, catching fish that it corralled into reach.

[GojiraGuy1954]

Mfw tail for display when you have a literal billboard on your back

[Shadowknight1]

I still find it difficult to believe Spinosaurus would spend much, if any time, on dry land with those tiny legs.  How could they possibly keep the rest of the bulk of the animal off the ground?

[suspsy]

Hippos are bad swimmers. They're even negatively buoyant. You push a hippo off a boat into the ocean or even a deep lake or river, that hippo is going to drown. 100% guaranteed.

And yet they spend the majority of their lives in water. Go figure.

[Sim]

Another new thing in this new paper is that it describes that Spinosaurus had hollow finger bones unsuited for bearing weight.

Please correct me if I'm wrong, but AFAIK Suchomimus was never thought to have a dip in its sail (like Ichthyovenator)? And there's controversy regarding the actual shape of Spinosaurus' sail. After the 2014 discoveries and I don't know why, the M shape became popular, but as of right now, my understanding is that both the M shape and the round shape are equally right.

The most recent Ibrahim paper gave Suchomimus and Baryonyx a dip in their sails for some reason, which is at odds with other reconstructions of Suchomimus such as this new Sereno paper's.

And yet this conflicts with the isotope data, which indicates Spinosaurus' body has below water most of its life, while the head above.

Even if the tail wasn't for propulsion, and even if it was a bad swimmer and diver, there's no way "around" that. Spinosaurus spent essentially its entire life in some water, doing something. Perhaps it didn't need to be a strong swimmer but floated calmly, catching fish that it corralled into reach.

Interesting, what is the source for isotope data indicating Spinosaurus held its body below water most its life?  I just remember isotope data indicating that some Spinosaurus spent a lot of time in water and others didn't.  Also I'm not sure this contradicts the isotope data you described, as the paper suggests Spinosaurus could have spent its time feeding immersed in water up to around 2.6m deep.

Mfw tail for display when you have a literal billboard on your back

I don't see a reason the back sail and tail couldn't both be for display, like in Hydrosaurus.

I still find it difficult to believe Spinosaurus would spend much, if any time, on dry land with those tiny legs.  How could they possibly keep the rest of the bulk of the animal off the ground?

The new paper says the legs of Spinosaurus were infilled probably to support its weight on land.

[Bread]

This is why I am holding off on buying any Spinosaurus figure. The next thing they'll find out is that it had a second set of arms or that it had wings

[stargatedalek]

I still find it difficult to believe Spinosaurus would spend much, if any time, on dry land with those tiny legs.  How could they possibly keep the rest of the bulk of the animal off the ground?

Loons and grebes have very similar proportions and despite incredible difficulty they spend a lot of time resting on land. An animal doesn't need to be a traditional biped to move sufficiently on land if it has other ways of avoiding predators (flight for said birds, perhaps size for Spinosaurus).

And yet this conflicts with the isotope data, which indicates Spinosaurus' body has below water most of its life, while the head above.

Even if the tail wasn't for propulsion, and even if it was a bad swimmer and diver, there's no way "around" that. Spinosaurus spent essentially its entire life in some water, doing something. Perhaps it didn't need to be a strong swimmer but floated calmly, catching fish that it corralled into reach.

Interesting, what is the source for isotope data indicating Spinosaurus held its body below water most its life?  I just remember isotope data indicating that some Spinosaurus spent a lot of time in water and others didn't.  Also I'm not sure this contradicts the isotope data you described, as the paper suggests Spinosaurus could have spent its time feeding immersed in water up to around 2.6m deep.

https://www.researchgate.net/publication/222090629_Oxygen_isotope_evidence_for_semi-aquatic_habits_among_spinosaurid_theropods
https://royalsocietypublishing.org/doi/10.1098/rspb.2018.0197

Sadly much of the references to this are scattered through other papers often with disparate conclusions that did not come up while searching specifically for isotope data.

[Sim]

Thanks for the links.  The first one though says the isotope data doesn't clearly support some Spinosaurus having an aquatic lifestyle.

[GojiraGuy1954]

Mfw tail for display when you have a literal billboard on your back

I don't see a reason the back sail and tail couldn't both be for display, like in Hydrosaurus.

Hydrosaurus' sail and tail are not nearly comparable to Spino's

[Sim]

I'd argue they are, but for a better comparison take the basilisk lizard which has prominent sails on its back and tail which are used only for display.  It even has a large crest on its head too.

[GojiraGuy1954]

I'd argue they are, but for a better comparison take the basilisk lizard which has prominent sails on its back and tail which are used only for display.  It even has a large crest on its head too.

What? Basilisk lizards are excellent swimmers.

[Sim]

Basilisk lizards don't use their sails for swimming.  It's mentioned in the paper:

However, cranial crests and spine-supported torso-to-caudal sails have evolved multiple times among extant lizard (agamids, iguanians, chameleons) for intraspecific display rather than aquatic propulsion. Semiaquatic sailfin and basilisk lizards (Figure 4B), for example, do not use their sails while swimming, spend very little time submerged, and are not aquatic pursuit predators.

[GojiraGuy1954]

Basilisk lizards don't use their sails for swimming.  It's mentioned in the paper:

However, cranial crests and spine-supported torso-to-caudal sails have evolved multiple times among extant lizard (agamids, iguanians, chameleons) for intraspecific display rather than aquatic propulsion. Semiaquatic sailfin and basilisk lizards (Figure 4B), for example, do not use their sails while swimming, spend very little time submerged, and are not aquatic pursuit predators.

Nobody is arguing Spinosaurus used its sail to swim either, it used the deepened tail that is obviously morphologically for propulsion

[Sim]

The tail of Spinosaurus has a sail too, from the new paper:

The caudal neural spines in S. aegyptiacus stiffen a bone-supported tail sail by an echelon of neural spines that cross several vertebral segments

The paper is arguing the tail sail of Spinosaurus was a display adaptation rather than a swimming one, which is what we've been discussing.  On that note, the tail of Spinosaurus isn't "obviously morphologically for propulsion" as this new paper argues against it with some convincing points including that:

In contrast, the distal tail of secondary swimmers such as crocodylians (Grigg and Kirshner, 2015), mosasaurs (Lindgren et al., 2013) and cetaceans (Fish, 1998) is expanded with pliable soft tissues free of bone to form a flexible caudal paddle or fluke (Figure 4C).

[stargatedalek]

But... basilisks do use their tails for propulsion. It may not be their primary function but they do make use of them secondarily. Also ignoring fish and newts which propel themselves just fine with thin surfaces for their tails (though newt tails are something of an in-between, being thin but also pliable).

[GojiraGuy1954]

The tail of Spinosaurus has a sail too, from the new paper:

The caudal neural spines in S. aegyptiacus stiffen a bone-supported tail sail by an echelon of neural spines that cross several vertebral segments

The paper is arguing the tail sail of Spinosaurus was a display adaptation rather than a swimming one, which is what we've been discussing.  On that note, the tail of Spinosaurus isn't "obviously morphologically for propulsion" as this new paper argues against it with some convincing points including that:

In contrast, the distal tail of secondary swimmers such as crocodylians (Grigg and Kirshner, 2015), mosasaurs (Lindgren et al., 2013) and cetaceans (Fish, 1998) is expanded with pliable soft tissues free of bone to form a flexible caudal paddle or fluke (Figure 4C).

Did they forget about eels