Spinosaurus Reconstruction Debate

This page discusses the debate regarding the lifestyle of *Spinosaurus*. This debate is referenced in multiple genus pages, however, it is not appropriate to include in any of those articles. If you are interested in learning about this debate, this page will attempt to explain. You are also encouraged to research these arguments on your own.

## 2014 Reconstruction

In 2014, paleontologist Nizar Ibrahim proposed a radical new reconstruction for the famous *Spinosaurus*. His model suggested that *Spinosaurus* was a quadrupedal specialist fish hunter. While, by the the time Ibrahim made his reconstruction, the fish-eating behavior of *Spinosaurus* was already known, it was still widely thought to have been a bipedal predator that was less suited to swimming.

The reason why Ibrahim assumed *Spinosaurus* was quadrupedal was due to his estimates regarding its center of gravity. If they are correct, then *Spinosaurus* was too front heavy to walk on two legs like other predatory dinosaurs.

This estimate also gave more modest proportions for *Spinosaurus*, perhaps being between 13 and 20 meters long, and possessing a more slender and gracile build than other giant predatory dinosaurs such as *Giganotosaurus* or *Tyrannosaurus*.

## Debate

While this reconstruction became common on the internet, and was featured on some television channels, many paleontologists were quick to challenge it. An alternative reconstruction shows a bipedal predator, acting comparably to a modern grizzly bear. While this depiction has *Spinosaurus* standing in rivers to catch fish, it also suggests that *Spinosaurus* was a competent hunter on land, perhaps occasionally catching its own food, or forcing other predators off of kills.

Isotopic analysis shows that some Spinosaurs spent proportionally more time around water than other predatory dinosaurs. However, some *Spinosaurus* populations spent a fairly normal amount of time on land. A paper published on researchgate stated that ''*Siamosaurus* specimens tended to have the largest difference from the ratios of other theropods, and *Spinosaurus* tended to have the ***least*** difference. The analysis showed that Thai spinosaurid teeth of *Siamosaurus* tended to have the largest difference from the ratios of other, more terrestrial theropods, while those of *Spinosaurus* from Tunisia and Morocco tended to have the ***least*** difference.'' The paper also points out that, of all the Spinosaurids, *Spinosaurus* possesses the least seemingly aquatic specializations and spent a considerable amount of its life as a Terrestrial theropod.

*Spinosaurus* does seem to have a lot of aquatic specializations. For example, its conical teeth are better suited for gripping slippery fish than slicing through flesh. It also possesses pores on the end of its snout, which could perhaps detect passing fish, like a crocodile. However, it should be remembered that this trait is not unique to *Spinosaurus*, nor is it unique to dinosaurs which are thought to have hunted in the water. *Neovenator*, for example, possessed some sensory organs on its snout.

Paleontologist Donald Henderson calculated the center of gravity of *Spinosaurus* using the leg proportions of related Spinosaurs. Henderson's estimates not only show that *Spinosaurus* had a normal center of gravity for a large theropod, but also that it would be somewhat awkward in the water, capsizing if it tried to swim, unless it frantically kicked its feet. His estimates are frequently cited to disprove the Ibrahim reconstruction. However, while insightful, they should by no means be taken as definitive. The only Spinosaur specimens that can be used for leg proportions belong to *Baryonyx* and *Suchomimus*. These genera existed long before *Spinosaurus*, meaning that the latter was more derived. Also, the individuals in question were sub adults. It is not uncommon for body parts to grow at different rates. Large Tyrannosaurs, for example, had proportionally longer legs when they were younger.

The final problem is that *Baryonyx* and *Suchomimus*, while related to *Spinosaurus*, are only related at the family level. The life styles of some other Spinosaurs, like *Baryonyx* in particular, are more known than *Spinosaurus*. However, two species in the same family can be quite different. As an example, the bear family contains specialist herbivores, Pandas, as well as generalists, such as black bears.

Henderson's calculations also indicated that *Spinosaurus* would be too buoyant, in other words, it could not dive to hunt fish under water. In addition to this, when diving, the sail would have produced quite a bit of drag.

In 2020, a *Spinosaurus* tail was studied. It was wide and paddle-like, and instantly seen as additional evidence for a semi-aquatic *Spinosaurus*. Analysis of a miniature version of the tail showed that it was far better for swimming than the tails of the other theropod dinosaurs studied, and similar to a crocodile's. However, this analysis was soon criticized for using miniature models, as the results might have been different if the models used were the size of a real *Spinosaurus* tail. Paleontologist David Hone stated "We don’t have too many good dinosaur tails, generally. It’s really quite weird in lots of ways, which is really interesting and really neat. But, I’m extremely unconvinced by some of the ecological interpretations that they placed on it.”

Despite the paddle-like shape, the vertebrae were greatly extended on top of the tail and less so on the bottom. This is quite different from modern crocodiles and newts, which have vertebrae on the underside of their tails which are much longer than on top. This suggests that at least the top extensions might have been part of the sail on the animal's back, perhaps used for display.

Paleontologist Mark Witton estimated that the tail was fairly stiff, only capable of about 3 to 4 degrees of motion. However, he noted that his estimates were "rough," as they could not take soft tissue into account without speculating. Therefore, the opinions of others can differ, sometimes quite significantly.

## What should I believe?

There is evidence both for and against *Spinosaurus* being a specialist fish hunter. Acceptance of the 2014 reconstruction does require a bit of assumption and speculation, however, it does not necessarily conflict with what we know thus far. Dr. Hone put it best when he stated that "It’s not that they’re wrong. It’s just I don’t think you can support that argument with the available data.”

The idea of a generalist *Spinosaurus*, while sometimes an awkward explanation of what some perceive as specializations, is more in line with what we know of other Spinosaurs.

In conclusion, a person can reasonably choose to personally believe either interpretation. However, if educating others in something like a presentation, the "safest" approach would still be to simply wait for more material.

## Read More

Buoyancy and stability issues https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6098948/

*Spinosaurus* Isotopic analysis https://www.researchgate.net/publication/222090629\_Oxygen\_isotope\_evidence\_for\_semi-aquatic\_habits\_among\_spinosaurid\_theropods