The New Spinosaurus

Spinosaurus has changed dramatically since I was a kid. The model I used to terrorize my other toys with looked like an overgrown Allosaurus with a giant sail on its back. As paleontologists rearranged the dinosaur family tree and found new species, however, they realized that Spinosaurus was a very different sort of animal, allied with croc-snouted, heavy-clawed dinosaurs like Baryonyx. When Spinosaurus finally tore up the celluloid in 2001’s Jurassic Park III, it was as a monstrous carnivore with giant claws, an elongated snout filled with conical teeth, and a flashy fin atop its back. And the evolution of Spinosaurus imagery has not stopped. A paper out in Sciencexpress today proposes that Spinosaurus was far stranger than paleontologists expected.

[The turn-of-the-century Spinosaurus. Today’s Sciencexpress paper suggests that the dinosaur was even more aquatic.]

The core of the new study, led by University of Chicago paleontologist Nizar Ibrahim, is a partial skeleton of Spinosaurus found in the 97 million year old rock of Morocco. The importance of the new specimen is in revealing parts of Spinosaurus never seen before. The skeleton includes parts of the skull and some vertebrae, but the real keys to the new Spinosaurus are the hips and hindlimbs.

The turn-of-the-century Spinosaurus popularized in Jurassic Park III and numerous pieces of paleoart stood tall over Cretaceous floodplains. But the hips and legs described by Ibrahim and coauthors look quite small and relatively weak. The femur – or upper leg bone – is short, yet has a robust flange of bone for a major leg-tail muscle retractor. And the foot bones of Spinosaurus are flat, with broad toe claws. This was not a dinosaur suited to running down prey. Spinosaurus, as envisioned in the new research, would have propelled itself through the water with strokes of its feet and sinuous flicks of its tail.

A new reconstruction of Spinosaurus. The red bones represent the parts of the new skeleton.  Model by Tyler Keillor, Lauren Conroy, and Erin Fitzgerald.
A new reconstruction of Spinosaurus. The red bones represent the parts of the new skeleton. Model by Tyler Keillor, Lauren Conroy, and Erin Fitzgerald.

Whether the new Spinosaurus best represents the real animal remains to be seen. The fantastic images of Spinosaurus that have come out of today’s media blitz are based upon a hodgepodge reconstruction that draws from many different dinosaurs. There’s the new subadult skeleton, digital representations of the original and long-lost Spinosaurus bones, vertebrae and hands that may or may not belong to Spinosaurus, as well as replacement parts from an assortment of spinosaurs, all scaled to fit together. The dramatic departure of Spinosaurus from the previous release is a hypothesis that will be tweaked as additional specimens are discovered.

Putting bones together is one thing, though. Understanding what those bones can tell us about vanished lives is another.

Spinosaurs stalked the shores of Cretaceous lakes and rivers. Paleontologists have known this for decades. The remains of fish and juvenile dinosaur bones found in the gut of Baryonyx – the dinosaur responsible for highlighting spinosaurs as oddballs – showed that these dinosaurs probably used their conical teeth and huge claws to nab prey in and around waterways. And geochemical evidence from spinosaur teeth further supported the notion that these carnivores stuck close to freshwater habitats. As paleontologist Thomas Holtz, Jr. has pointed out, spinosaurs were likely the dinosaurian equivalent of grizzly bears.

A reconstruction of the skull of Spinosaurus, with known elements in blue. Art by Davide Bonadonna.
A reconstruction of the skull of Spinosaurus, with known elements in blue. Art by Davide Bonadonna.

Spinosaurus itself may have done more than just wade into the shallows, though. Ibrahim and colleagues point out several lines of evidence for swimming Spinosaurus. Some are relatively weak. The nasal opening of Spinosaurus, Ibrahim and colleagues note, is retracted up the snout, possibly to stop the dinosaur from inhaling water. But the dinosaur’s fleshy nasal opening was probably far forward of the bony aperture, and some semi-aquatic animals – such as crocodiles and hippopotamus – have their noses at the tips of their snouts. A retracted nasal opening isn’t a dead giveaway.

Better evidence for swimming Spinosaurus comes from the structure of the dinosaur’s bones. The dinosaur’s long bones are solid. This is odd.

Spinosaurus was a theropod – a member of the major lineage that includes dinosaurs such as Tyrannosaurus and Allosaurus – and these dinosaurs typically had relatively light long bones with cavities inside. The dense Spinosaurus bones, by contrast, seem similar to those of some early whales and other semi-aquatic mammals that evolved heavy bones to act as a kind of internal ballast. Based upon what paleontologists have previously discovered about animals that transition from land to the water, the solid leg bones of Spinosaurus are the best evidence that this was a dinosaur that preferred to swim. Trackways have shown that other theropods swam from time to time, but Spinosaurus may have been unique in its dedication to a semi-aquatic lifestyle.

David Martill, Nizar Ibrahim, Paul Sereno and Cristiano Dal Sasso at the site of the new Spinosaurus. Photo by Cristiano Dal Sasso.

And then there’s that fin. Ibrahim and colleagues hint that the sail of Spinosaurus might have been a way to add some extra weight for staying submerged. That could be true, but it doesn’t explain how such a sail evolved in the first place.

Smaller spinosaurs, such as Suchomimus and Ichthyovenator, had sails, too, and they don’t share the proposed aquatic adaptations that Spinosaurus did. Spinosaurus inherited that sail rather than evolving it anew. The sail of Spinosaurus could have been an aid in adding weight, a prominent display structure, or even a way to store energy to help propel itself as it swung its tail from side-to-side, or even all three. The point is that if we’re going to understand why Spinosaurus was so gaudy, we need a deeper perspective on spinosaur evolution.

The function and evolution of spinosaur sails will continue to be debated. But one thing’s for sure – Spinosaurus surely wasn’t able to sneak up on any dinosaurs coming down to the water for a drink. The sail of Spinosaurus would have jutted above the surface as it swam along, advertising its presence.

Spinosaurus couldn’t have spent all of its time in the water, though. All dinosaurs laid eggs, and that, at the very least, required journeys into the terrestrial realm. Based on the proportions of their new reconstruction, Ibrahim and coauthors suggest that Spinosaurus must have walked on all fours while on land. This looks intuitive given the heavy arms and comparatively puny legs of the new Spinosaurus, although future reconstructions and biomechanical analyses could contradict the image of Spinosaurus as a paddling, four-on-the-floor dinosaur.

Spinosaurus isn’t done changing. The new subadult described by Ibrahim and colleagues fills in parts of the dinosaur’s skeleton that have been a total mystery until now, but the fact remains that most of the new reconstruction is assembled from bits and pieces of various dinosaurs. It’s a hypothesis. Spinosaurus was undoubtedly a spectacular dinosaur, but just how strange this prehistoric piscivore truly was is a secret still held tight by the fossil record.


Ibrahim, N., Sereno, P., Dal Sasso, C., Maganuco, M., Martill, D., Zouhri, S., Myhrvold, N., Iurino, D. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Sciencexpress. doi: 10.1126/science.1258750

25 thoughts on “The New Spinosaurus

  1. First comment right here and also, in the page. I want to greet you for your excellent work in the divulgation of dinosaurs in the media. Recently I read your book My Beloved Brontosaurus and I think is one of the best books about the subject I’ve ever read.

    About Spinosaurus, I’m simply shocked. I was thrilled with the news from Sereno, but now, I see this creature was more bizarre than we ever imagined. The way the legs and arms are positioned shows Spinosaurus had a different anatomy fron other relatives like Baryonix or Suchomimus. This means Spinosaurus was a more specialized form for fishing than others.The sail is something I though continuosly that it could had a function for better swimming. Know, it confirms it.

    This also could explain coexistence of Spinosaurus with larger predators like Carcharodontosaurus or Bahariasaurus. They simply ocuppied different ecosystems and feed on different preys.

    Now, it’s only time to see the new incredible reconstructions that will make paleoartists.

  2. Hold up. Full stop. Look at that skeletal. Are the authors suggesting those legs are properly scaled and not a juvenile or, possibly, a different animal entirely? That seems completely untenable.

  3. I’m with you, Zach. There is something really odd about the hind limbs. The proportions of the femur, tibia/fibula, metatarsus, tarsals and toes do not suggest an aquatic, amphibious or even a wading lifestyle animal. In all of those forms, the long bones become shorter and the pes becomes much longer. Instead the proportions are those of a terrestrial, cursorial animal. It really looks like a chimera.

  4. Still, we need more specimens, now they need to find, if lucky enough, hatchlings or even younger Spinosauruses. I’m in favor with the adult having short legs for now. Who knows if they scanned those legs and showed they came from mature individuals? We need to wait and let them investigate further. Still, Spinosaurus is one of the most unmaginable theropods ever to walk on our planet! Congrats Dr. Sereno and Dr. Ibrahim, and thanks for posting this very great news that I’ve waited for, Brian Switek.

  5. I speculate that the sail, projecting above the waterline whilst most of the animal was submerged and not easily visible, may have acted as a territorial display to other Spinies. It allowed an animal to be visible to others of it’s species while hunting possibly acting as a warning to males and an attractive feature to females. Or, acted to maintain spacing to avoid accidental encounters that might lead to conflict and injury. Perhaps it also was involved in thermoregulation warming the blood when broadside to the sun thereby allowing the animal to remain in the water for longer periods. It could submerge or roll on one side to cool the sail if it was overheating.

  6. Well, Scott Hartman seems to have found an issue with the scaling of the hindlimbs in the reconstruction versus the tabulated measurements. So perhaps the whole quadrupedal thing doesn’t hold up.

  7. Excellent restoration, congratulations Davide Bonadonna! As regards the function of the sail, it seems likely that quite substantial aerodynamic forces would be generated by it, even in a moderate breeze. Appropriate angling at the cranial end of the “sail” (an unusual, but probably feasible, horizontal twist in the shoulder/neck joints) would produce forward thrust, capable of assisting the animal in moving almost directly into the breeze, and very powerfully at right angles to the wind, at the cost of some sideways movement. The webbed limbs, and a deep profile for the gastralia (somewhat different from the current restoration), would create a keel. It’s hard to imagine that the animal would not exploit the forces that would be generated from the “sail”, both for display and movement. It would be nice to make a 3D model showing this. Perhaps Spinosaurus was the first sailing dinosaur?

  8. Even though this is new news, I prefer the other looks of the Spinosaurus much better!! This size makes it look smaller then what it did, besides that what bones did they change out of what were the spinos’ back legs? They pretty much changed the spino to an over grown dimetrodon I think thats haow you spell it.

  9. I believe that Ibrahim’s Spinosaurus skeleton was in fact a juvenile specimen, as was another that they used in their analysis. My thoughts now go towards Jack Horner’s theory on the change in dinosaur anatomy during the aging process. Could it not be possible that only at a certain point in this dinosaur’s life did it actually look as they suggested, and in fact the hind limbs grew as it matured.
    I don’t know what advantage that this might give it, but surely it might be possible.
    I struggle to see an animal of that size quadrupedally walking (especially with pronated forelimbs), and additionally I fail to see what skill it would have at fishing with that huge sail. It could not easily ambush land predators like a crocodile, and underwater movement seems unlikely, as does the agile pursuit of fish. The only reasonable hunting behavior that I can think of is it remaining still floating on the surface of the water and then quickly snatching prey as it neared. However, the anatomy (eye positioning, solid bones) does not really lend itself to this. I’d like to know if anyone had any other ideas about behaviors.

  10. I visited the National Geographic Museum today and saw the Spinosaur skeleton. It struck me that the torso looks like the hull of s boat and the sail looks like, well, a sail. The proposed explanations for the sail in the exhibit didn’t list that possibility. Afterwards I looked up this article by Brian Switek and noticed Simon C.’s comment about the aerodynamic properties of the sail. He suggests that the sail could have been used for propulsion, a great idea. And even if is wasn’t capable of much forward thrust, it could still have provided downwind motion. Indeed, it would have been hard to avoid. A silent drift would be a great advantage for a large predator stalking fish. The Spinosaur could enter the water upwind (or swim there) and coast across the area to be fished, waiting for unwary prey. It would then return upwind or to shore by swimming. This technique might have some advantages over noisy paddling or walking in shallow water.

  11. Thanks Don! I think the idea of the sail to providing movement towards prey without paddling is excellent. Paddling would produce distinctive pressure waves that fish must have learned to be very wary of, given that plesiosaurs and turtles used such movements. I tried out a small floating model of a spinosaur in the sea off Seaton beach in the UK, but the model was only ~30cm long, and the main aerodynamic effect seemed to be to roll the model sideways. I think I need a larger model, or a smaller test arena!

  12. I wonder if the one they found was just one of many and that one had just adapted to an area that required those ligaments.

  13. I think the whole quadrupel idea is not correct. If you compare spinosaurus to other spinosaurids, no other is a quadrupel, and they were adapted to fishing too. Baryonyx and suchomimus walked on two legs, so why would spinosaurus be on 4? Plus I think spinosaurus was the apex predator of its time. If it was similar to crocs, it would base its diet off of size. Those croc like jaws would’ve been weak to open, but strong to close, and it probably shook its prey like crocs do today. This would allow it to hunt both fish and other dinosaurs

    1. beacause they are different dinosaurs? humans and gorillas both belong under hominiae (subfamily) but we dont look the same or have the same features.

  14. If spinosaurus really walked on all fours on land with hands adapted to grab fish and prey, then this is no longer my favorite dinosaur.

  15. I have an idea. Spinosaurus, when it came out of water, it would walk on all fours. To attack prey like sauropods, it would use its powerful front legs to propel its self onto its hind legs and go for the long neck. When confronted by a large carnivore, it would do the same thing.

  16. there is no possible way those legs could support a dinosaur they look like twigs. the scientists who decided this were probably still upset about the spino killing off the rex in jurassic park 3. while i do believe that it was aquatic i believe it behave more egret or heron like and therefore needed strong hind legs to support its body weight, additionally in the current form the spino would be easy prey for a super croc and would need the speed from larger hind legs in order to escape.

  17. As Holtz, I believe, observed, these reconstructions based on scaling up or down parts from various finds and then sticking them together most often results in a bizarre chimaera. This “new” Spinosaur is just such an animal. What is absolutely certain, however, is that whoever thought up this “aquatic belly-crawler” has never been in water deeper than a wading pool. I cannot imagine an animal more ill-suited for swimming than one with a large sail on its back. Ask any boat designer just what that does to a vessel’s seaworthiness and the error becomes apparent.

  18. I seriously doubt that Spinosaurus was a quadruped. Am I open to the possibility? Yes, but I think more evidence is required. The biggest flaw I see in this theory is the fact that we see no evidence of it in any other members of the Spinosauridae family. In all of the other members of the family for which we have recovered at least some of the bones in the limbs, the animals seemed to clearly be bipeds. Some of these species even have complete forelimb fossils. When one examines these remains, it becomes clear that Spinosaurid forelimbs were perfect for grasping prey like slippery fish and smaller dinosaurus, but were poorly suited for supporting the weight of these animals. Furthermore, the reconstruction of these species were based on the remains of individuals, not a combination of different specimens like the new Spinosaurus. Unless new evidence is found, I think it’s safer to assume that Spinosaurus was a biped with shorter hindlimbs (though not as short as Ibrahim claims) than other theropods.

  19. If you look at the forelegs, they look like they wouldn’t be efficient for walking. Compared to other quadrupedal animals, they look like they would not allow for proper balance or weight baring. With that in mind, the hind legs look far too small to bare the weight of the whole body. especially with where the center of gravity is placed. With the way the skeleton looks, it appears, to me at least, that it could never leave the water without practically hauling itself out, using quite a bit of energy, something animals try to avoid without a proper reason to do so.

  20. I seriously doubt that Spinosaurus was bipedal. The arms of the dinosaur, while powerful and robust, where not strong enough to support the weight of a dinosaur as massive as Spinosaurus. The specimen in question was probably a juvenile or a chimera.

  21. Uggghhhhh no there is just no at all it looked like that. LooK it’s relatives they are all bilateral creatures. And that sail to won’t catch good wind because of that dip near the center. The arms and legs looks more like a lizard and less like a crocodilian and really wouldn’t support it’s body or the sail. All in all the when from old 1900s American t rex with a a huge fin on its back to this … well this.

  22. The one thing i don’t get is that, why do they add on other bones from different Dinosaurs to Spino and say oh this is what it looks like, I mean those back legs don’t even look like they belong to Spino. So why would they add another dinosaurs bones to Spino if it did not belong to the same animal?

  23. This is so stupid. If spino, according to the “new” theory, was a quadraped it would have been so weak to stand. With such a massive body size, those legs look unusual. And also this is just one specimen which could be of a baby spino, they canno4 conclude anything on the account of one specimen. Suchomimus like dinosaurs were bipeds and so was spino. Look at documentaries about spino from different sources, you would see a clear cut difference. If a spino had such weak limbs it could never afford such a massive size. I appreciate the effort but coming up with a complete parallel and “assumption-based” theory is really stupid. Find and study more of specimen and make a theory. Dont jump 20 conclusions with a single specimen that could have been of a baby spino or a completely different dinosaur!!

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