Spinosaurus Sail - for Thermoregulation/Fish Catching - New Paper

[Simon]

Pretty fascinating stuff, and it makes as much sense as some theories - the dual purpose might actually be a tri-purpose (this paper doesn't address the recent theory about tall neural spines acting like anchors for long ligaments and muscles to help keep the front of the animal suspended/balanced).

The thermoregulation theory is kind of a common - sense conclusion (since the sail would stick out of the water, using it as a "sun sail" to warm up the animal which was otherwise submerged in cooler water has a kind of obvious inevitability and would allow that animal to remain in the water longer.  Depending on the time of day and temperature, turning head-on or tail-on into the sun would also keep the animal from warming too much at high noon.  The "fish-catching" aspect of the sail is an especially ingenuous theory.  Fish indeed tend to flock to shady spots when its hot and sunny, a.snd the shade of a massive sail just might attract them - the easier to be chomped on by the Spino....fascinating how there is a bird today that uses its wings to create shade for fish and then catches them.

https://peerj.com/preprints/2917/

[CrypticPrism]

To be honest, I expected this to be the cause. Although I have to agree with the musculature one too, it seems feasible.

[Cloud the Dinosaur King]

Wouldn't the sail be used for attracting a mate as well, or is that what the crest was for?

[Appalachiosaurus]

Honestly, Thermoregulation seems to be more of a bonus than the main cause. Crocodiles do just fine without a huge sail sticking out of their back and they're cold-blooded, unlike the warm-blooded spinosaurus which lived in a thick and humid swamp. Maybe if it lived in a more polar area, but North Africa at the time was pretty much a giant deep tropical swamp. I'm still partial to them using it as a display feature, it is funny to think what funky ideas future paleontologists come up with for Peacock feathers (like maybe it was used for prolonged flights or to catch wind and sail when sitting on the water) when we know they were pretty much entirely used to communicate. I believe Spinosaurus was the same way.

[WarrenJB]

I'm sceptical about the thermoregulation bit, after all that's written about plates and fins and how the 'turn to the sun' hypothesis has problems. Can't help but think there are a few large, extant, aquatic or semiaquatic animals that keep themselves warm enough without dorsal frills.
The comparison to black heron behaviour sounds a little iffy too. For one thing, a vertical frill (rather than horizontal wings) doesn't sound much use with a high sun - with the caveat that Spinosaurus could have been a typical predator, lying up during the hottest part of the day. The black heron also sets up so that the business end (sharp beak and striking neck) is aimed at the middle of the shadow. I have trouble imagining a 15m Spinosaurus turning 90° in the water to strike into it's own shadow, with anything remotely like a similar turn of speed; especially if the sail is partially submerged. It'd be like trying to spin an oil tanker...

Maybe I'm wrong, but that's the impression I get.

Crocodiles do just fine without a huge sail sticking out of their back and they're cold-blooded, unlike the warm-blooded spinosaurus which lived in a thick and humid swamp.

Yeah, that!

[ZoPteryx]

I'm sceptical about the thermoregulation bit, after all that's written about plates and fins and how the 'turn to the sun' hypothesis has problems. Can't help but think there are a few large, extant, aquatic or semiaquatic animals that keep themselves warm enough without dorsal frills.
The comparison to black heron behaviour sounds a little iffy too. For one thing, a vertical frill (rather than horizontal wings) doesn't sound much use with a high sun - with the caveat that Spinosaurus could have been a typical predator, lying up during the hottest part of the day. The black heron also sets up so that the business end (sharp beak and striking neck) is aimed at the middle of the shadow. I have trouble imagining a 15m Spinosaurus turning 90° in the water to strike into it's own shadow, with anything remotely like a similar turn of speed; especially if the sail is partially submerged. It'd be like trying to spin an oil tanker...

Maybe I'm wrong, but that's the impression I get.

Crocodiles do just fine without a huge sail sticking out of their back and they're cold-blooded, unlike the warm-blooded spinosaurus which lived in a thick and humid swamp.

Yeah, that!

Agree on all accounts.  Display combined with a biomechanical function seems most likely, although its worth noting that none of the proposed uses are mutually exclusive.  That said, I kind of doubt this manuscript will make it past peer review...

[Simon]

Honestly, Thermoregulation seems to be more of a bonus than the main cause. Crocodiles do just fine without a huge sail sticking out of their back and they're cold-blooded, unlike the warm-blooded spinosaurus which lived in a thick and humid swamp. Maybe if it lived in a more polar area, but North Africa at the time was pretty much a giant deep tropical swamp. I'm still partial to them using it as a display feature, it is funny to think what funky ideas future paleontologists come up with for Peacock feathers (like maybe it was used for prolonged flights or to catch wind and sail when sitting on the water) when we know they were pretty much entirely used to communicate. I believe Spinosaurus was the same way.

I agree that the sail probably had multiple uses.  As far as Crocs go - they do have to spend lots of time outside the water getting warmed up by the sun.

The fish-catching hypothesis was a bit of a stretch, I agree.

[Neosodon]

I've heard before that it could be used to warn off rivals. As Spinosaurus swam a crossed a lake its sail would stick out of the water warning every other predator that this is my lake.

[BlueKrono]

I've heard before that it could be used to warn off rivals. As Spinosaurus swam a crossed a lake its sail would stick out of the water warning every other predator that this is my lake.

I once saw a moose swimming across a lake, and that was already impressive. I once heard a northwoods Native American tribe had a right of passage where the young man would have to ride a moose to become a man. The only way to do this and survive was find one swimming across a lake, paddle out to it in a canoe, jump out and swim to it, and mount it in the water where humans have the agility advantage. Once the disgruntled moose reached a shore and the hooves touched down the young man dismounted and swam back out into the lake, the only safeish place for a human in the presence of a disgruntled moose. This technique might not have worked so well for northwoods Native Americans who lived with the spinosaurs though.