Re: Spinosaurus dorsal sail function riddle

[Mike Habib <biologyinmotion@gmail.com>]

The authors do consider submersion versus surface swimming - but only by using 
the most simple of scaling regimes (essentially lumping all semiaquatic 
vertebrates together and saying that the lung volume follows isometry, more or 
less). I was particularly interested in their hypothesis of a “hydrodynamic 
fulcrum” function for the sail (mostly because, I admit, I was immediately 
skeptical).

The entirety of that argument turns out to be this:

"While smaller dorsal sails or fins make the dorsal water volume better 
accessible for slashing, it can be speculated that their smaller stabilization 
effect makes lateral slashing less efficient (e.g. for thresher sharks). 
Forming a hydrodynamic fulcrum and hydrodynamically stabilizing the trunk along 
the dorsoventral axis, Spinosaurus’ sail would also have compensated for the 
inertia of the lateral neck by tail movements and vice versa not only for 
predation but also for accelerated swimming. This behaviour might also have 
been one reason for Spinosaurus’ muscular chest and neck reported by Ibrahim et 
al. (2014).”


Cheers,

—Mike


> On Nov 17, 2015, at 6:37 AM, Jaime Headden <jaimeheadden@gmail.com> wrote:
> 
> Until they realize that the nearly solid bones of the sail are
> counter-intuitive to flotation, as argued by Sereno at this years'
> SVP, and in general contradiction to previous arguments for a bouyant,
> crocodilian-like surface swimmer.
> 
> On Tue, Nov 17, 2015 at 6:26 AM, Ben Creisler <bcreisler@gmail.com> wrote:
>> Ben Creisler
>> bcreisler@gmail.com
>> 
>> A new paper:
>> 
>> Jan Gimsa, Robert Sleigh and Ulrike Gimsa (2015)
>> The riddle of Spinosaurus aegyptiacus' dorsal sail.
>> Geological Magazine (advance online publication)
>> DOI: http://dx.doi.org/10.1017/S0016756815000801
>> http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10036572&fulltextType=RC&fileId=S0016756815000801
>> 
>> Spinosaurus aegyptiacus was probably the largest predatory dinosaur of
>> the Cretaceous period. A new study shows that it was a semiaquatic
>> hunter. The function of Spinosaurus’ huge dorsal ‘sail’ remains
>> unsolved, however. Three hypotheses have been proposed: (1)
>> thermoregulation; (2) humpback storage; or (3) display. According to
>> our alternative hypothesis, the submerged sail would have improved
>> manoeuvrability and provided the hydrodynamic fulcrum for powerful
>> neck and tail movements such as those made by sailfish or thresher
>> sharks when stunning or injuring prey. Finally, it could have been
>> employed as a screen for encircling prey underwater.
> 
> 
> 
> -- 
> Jaime A. Headden
> The Bite Stuff: http://qilong.wordpress.com/
> 
> 
> "Innocent, unbiased observation is a myth" - P. B. Medawar (1969)