Spinosaurus has no sail

There are popular mainstream beliefs that are just plain wrong.

One of them, is the issue I shall address: Sailbacked Spinosaurs.


Spinosaurus has traditionally been depicted with a sail. Jurassic Park 3 is also to blame for this as well.

But just because it's depicted as such, doesn't mean it's true. In fact, it's in this case, it's pretty wrong.

The comparisons used to give Spinosaurus a sail are Dimetrodon and Edaphosaurus, they even literally put a Dimetrodon sail on a spinosaurid's body in some reconstructions, like the one shown below:

Spinosaurus does NOT look like this!

Whoever made that depiction, obviously did not look at, or completely ignored, the fossils.

Spinosaurus holotype IPHG 1912. Note the broadness of the spines, and the fact that they look nothing like that of Dimetrodon.

By looking at the fossils, it's pretty obvious that Spinosaurus' neural spines looked nothing like a sailback's. In fact, Spinosaurus spines actually resemble bison and chameleon spines more(not perfect matches though) than those pathetic thin rods.

Spinosaurus skeletal reconstruction by Scott Hartman. Note the broadness and the spacing of the spines. There's little space between each neural spine. Image only used for illustration. I obviously have no claims towards this image.

Bison skeleton. The tall elongated spines support a heavy hump. The spines are close together, and are broad, like Spinosaurus. However, the bison's neural spines are thicker in frontal view, and that's where the chameleon comes in.

Chamaeleo melleri, a ridgebacked chameleon. it's spines also compare to Spinosaurus', but isn't as elongated, and the chameleon's spines are spaced farther from each other than that of bison and Spinosaurus.

Chamaleo melleri, in the flesh. There is no clear distinction between ridge and back.

The dorsal structure of Spinosaurus seems to possess attributes of both bison and chameleon spines. It is therefore likely that Spinosaurus had a ridge. It would have looked like a vertically-elongated triangle with a somewhat thin and rounded top in cross-section.

The neural spines of sailbacks only have to support itself and a vascular network. They can, and do get thinner distally, from all directions. This is not the case with Spinosaurus.

No suitable comparison can give Spinosaurus a skin sail.

Oh, and here's the Dimetrodon and Edaphosaurus stuff:

Dimetrodon skeleton. Note the thin rod-like spines, which look absolutely NOTHING like the ones found in Spinosaurus.

Edaphosaurus skeleton. Again, a total lack of resemblance to the spines of Spinosaurus.

Those sailbacks have spines which, aside from being long and elongated, have nothing in common with that of Spinosaurus!

In the top image, I have photoshopped a Spinosaurus restoration, to incorporate the more likely dorsal structures. The same has been done with the Ouranosaurus carcass. Here is the original, and very wrong, image.

Whether that structure is muscle or fat remains is still debatable.

With this, we can say, that a Dimetrodon-backed Spinosaurus is silliness.

If it had a sail, why would it evolve broad spines, when thin rods could have done the job?

Simple answer: It did NOT evolve a sail. Animals do not waste energy developing useless structures.

How large is UCMP 137538, really?

Many of you who are interested in dinosaurs, may have seen people in forums and youtube who fuzz over the legend of the "14-15 meter Tyrannosaurus", and refer to the specimen "UCMP 137538".

UCMP 137538 is known from a single 13-centimeter long pedal phalanx, which has been assumed to be a left pedal phalanx from comparisons with FMNH PR2081. That is a weak assumption, as the bone looks quite different from that of FMNH PR2081.

For starters, it may not even be a tyrannosaurid. It could have been a gigantic therizinosaur, since a herbivorous lifestyle isn't limited by the constraints of a carnivorous one, such as the need to run down prey. If you read the paper about UCMP 137538, you will see that the only real diagnosis done is the one assigning it as a theropod.

It's assignment to Tyrannosaurus is based on nothing but size and location, both of which are weak arguments for assigning isolated fossils to specific genera/species. It's also partly based on the assumption that Tyrannosaurus is the only large theropod living at North America at the Maastrichtian age, which is quite an almost-baseless assumption, considering that the vast majority of the dinosaurs are very likely undiscovered.

It's placement within the foot is also uncertain, the paper bases it's placement on nothing but superficial appearance.


Then how large would it be?




Answer: Completely unknown.


The problem is, it's just an isolated toe bone. Even the enigmatic Amphicoelias fragillimus is known from better remains(A D9/D10 vertebra).

The giant sizes come from scaling it up from FMNH PR2081, and the naive fanboys seemingly only scale from that specimen. FMNH PR2081 isn't the only tyrannosaur specimen however. And Tyrannosaurus isn't the only tyrannosaur. For all we know, UCMP 137538 may actually be a non-Tyrannosaurus tyrannosauroid.

Even IF it was a Tyrannosaurus or a very similar genus, you should still stay away from those 14+ meter calculations. Tyrannosaurus specimens can show quite a lot of variation.

BHI 3033(~10.9 meters, probably around 6 tonnes?), has toe bones that come close in size to that of FMNH PR2081. Not to mention that with pathogeny, digit bones can vary greatly even within individuals.

It is entirely possible that UCMP 137538 may actually be smaller than FMNH PR2081(~12.3 meters, ~8 tonnes).