spinosaurus

[darylj]

Another question,
wanted to know peoples opinions on the dinosaur spinosaurus, and in-particularly the sail / hump.

what are peoples views on why this evolved, what it was for, and why similar species (baryonx) didnt have the same feature.

[Zopteryx]

Most scientists agree that the long spines of Spinosaurus supported a sail rather than hump.  The hump theory, I believe, was mainly supported by scientists who favord a quadrepedal or semi-quadrepedal posture for Spino.  We are now pretty certain that therapods could not adopt that pronated hand posture, and knuckle walking seems even more unlikely.  I imagine the sail was a little thicker then the shrink-wrapped version oftne portrayed, but I wouldn't call it a hump.

As for function, the theories vary.  It almost certainly had a display function, considering how prominent it would have been.  A likely second function was thermoregulation, the large surface area could capture or disipate heat quickly.  It has also been suggested that the sail helped Spino to catch fish by creating a shadow that the little fishies would want to hide under, only to be eaten!  I find this theory a little unlikely though, due to the odd angle the Spino would have to grab the fish at.  For completeness sake, if you favor the hump theory, it would have acted as either an area for fat storage or the attachment point for muscles.

And as a final note, Spino wasn't the only spinosaurid with a sail like structure on its back.  Suchomimus and the newly discovered Ichthyovenator also had sails.  Spinosaurus just took this feature to the extreme.

Hope this help!

[darylj]

thanks for the response.
I am also in favour of the sail over the hump theory.

am i wrong in thinking that the sail as method of display would have been a secondary function? i mean thats a pretty strange thing to evolve solely for display.
i have also heard about the fish shadow idea, which seems unlikely.
then theres the thermo regulation idea... which i believe would mean the sail had the same use as dimetrodon,,, conveniently.
the only issue i have with both of these theories is that baryonyx filled essentially the same niche as spinosaurus, yet clearly didnt need a sail to either hunt or thermo regulate... even suchomimus managed without a large sail.

so when we look at suchomimus, do we think that its small sail was used for thermo? or shadow fishing? because this seems more unlikely.

[Zopteryx]

Well, antlers are pretty strange, and they evolved solely for display and competition within the species.  But yes, display was likely a secondary benefit, but it probably evolved rapidly once started.

Baryonyx lived a slightly cooler climate than Spino, so perhaps its own body heat was enough to sustain itself.  Suchomimus and Spino lived in similar climates, but evolved different shaped sails.  This is probably because Suchomimus spent more time in the water, keeping it cooler, while Spino was more terrestrial.  This habitat theory is supported by a recent chemical analysis of spinosaurid teeth.  Spino may have also needed its large sail to help scare off equally large competition, like Carcharodontosaurus.  It's also important to note that within the Spinosaurid family, there are the subgroups Baryonychinae (Baryonyx, Suchomimus, Ichthyovenator) and Spinosaurinae (Spinosaurus).  The former group had low, long sails; while the latter group had relatively short, but tall sails.  So sail size could just be more of a matter of genetic lineage than function.

No matter what, there's too little fossil evidence to support much of this for certain.

[darylj]

to be honest i dont know enough about thermoregulation... il have to do some research.
is there any evidence that spinosaurus was more terrestrial than say, suchomimus?

i long for some more spinosaur finds... there just havnt been enough!

what do people think / know about the evolutionary path of spinosaurids? i read a piece recently suggesting a lineage orriginating with dilophosaurus... based on the notch in the skull.... interested me

[Gryphoceratops]

"am i wrong in thinking that the sail as method of display would have been a secondary function? i mean thats a pretty strange thing to evolve solely for display."

Look around at what animals today will do at their own expense just for the sake of mating.  My favorite example is the male peacock.  Those tail feathers are so cumbersome the poor bird can't fly very fast, has its field of vision cut in half every time it spreads them out, plus is cursed with an insane color pallet that makes it stick out like a beacon to predators (lots of male peacocks fall victim to tigers and leopards).  A spinosaurus evolving a few elongated neural arches doesn't really seem like a big deal anymore.   

[Zopteryx]

to be honest i dont know enough about thermoregulation... il have to do some research.
is there any evidence that spinosaurus was more terrestrial than say, suchomimus?

i long for some more spinosaur finds... there just havnt been enough!

what do people think / know about the evolutionary path of spinosaurids? i read a piece recently suggesting a lineage orriginating with dilophosaurus... based on the notch in the skull.... interested me

Thermoregulation is simply the way an animal regulates its body temperature for maximum energy efficiency.  Most (if not all) therapods were "warm-blooded", that put big animals like Spino (which lived on the equator) at great risk of overheating, so big surfaces like a sail were great for dissipating heat quickly or collecting it quickly if needed, making the animal more active sooner and better able to respond to stimuli in its environment.

Saying that Spino is terrestrial is relative to other spinosaurs, compared to other therapods Spinosaurus was highly aquatic.  An oxygen isotope study on therapod teeth backs this up.  The study found that most therapods spent little time in the water, with spinosaurs being the exception.  However, within this group there was variation, from most aquatic to least aquatic: Siamosaurus, Irritator, Suchomimus, Baryonyx, Spinosaurus.  Siamosaurus spent by far the most time in the water (a possible indication that the teeth tested were actually from a crocodile); Irritator, Suchomimus, and Baryonyx all tested very closely to one another; and Spinosaurus was shown to be far less aquatic than the others (but still more aquatic than other types of therapods).  This makes sense for Spino, being so big meant he'd need a lot of food; so, in addition to fishing, he probably also scavenged or hunted small prey inland.

As for the evolution of spinosaurs, they are believed to have arisen from the megalosauroid group of therapods, probably during the late Jurassic.  While no "missing link" has been discovered, some megalosaurids like Dubreuillosaurus had rather long & strong arms and longer skulls, possible evidenve of the connection between the two groups.  I've heard the dilophosaurid origin theory too, but I think most scientists don't accept it, the notch in the upper jaw is just an example of covergent evolution.

As for more discoveries, I think just about everyone on this forum would be thrilled if a mostly complete spinosaur specimen was found!   There's rumored to be an almost complete, but as of yet undescribed, juvenile Spinosaurus specimen in exsitence.

[Sharptooth]

Frankly i don't think Suchomimus had a sail... His neural spines are quite low, more reminiscent of a hump or a well-muscled back than of a sail, like in Spino's case.

Why Spino should have evolved such a big structure on his back, well, as Griff said, display could be an answer (maybe only males had it)... Or maybe it worked like a fin and helped him to swim faster (if he was really a semi-acquatic animal as some people suggested).

[darylj]

if suchomimus spines were for a hump then wouldnt it suggest that spinosaurus had jsut a larger hump?
im sure wether it was hump or sail that they both had the same feature... just a different size.

with regards to a fin... on a 15m long predator... all its gonna do is make you extremely visible. and besides, some of the 'more aquatic' speices lacked the spine.
i guess thermoregulation is poosible... but i dont understand why spinosaurus would need to cool down when other large predators in the same area managed without a sail...?
this says to me either... spinosaurus hunted in the day and other large predators were nocturnal (or vise versa?)
or
spinosaurus stood, like a heron, in the water... for hours on end (fishing) and the sail being out of the water kept the creature warm? (is tht a possible 'thermoregulation use?)

[DinoFan45]

It's not necessarily an inhibiting factor for hunting. If you look at large mammals today, you would be surprised to find that, at least for me, they can be relatively quiet when they want to. If only we could see the skin colors, then it could help.

[Sharptooth]

if suchomimus spines were for a hump then wouldnt it suggest that spinosaurus had jsut a larger hump?
im sure wether it was hump or sail that they both had the same feature... just a different size.

Not at all; different species of the same family can exhibit a vast array of different physical traits, it happens quite often in modern animals too 

That's why i usually dislike when paleoartists sometimes restore a dinosaur making him look a carbon-copy of another, better-known relative... 

[darylj]

Fair… but im just saying that spinosaurus, irritator, suchomimus etc all share a common ancestor… and that creature had reason to develop the beginnings of either a humo or a sail… so it seems unlikely that if say this was a sail, that one member of the lineage would lose that and then find the need to develop a hump.

Personally im very much the opposite and think that animals of the same lineage should be used to fill the gaps.

[Sharptooth]

Bear in mind that, if you look at all the spinosaurids discovered so far, the only one who looks to have had a proper sail is S. Aegypticus; Baryo, Sucho and Irritator (or Angaturama) seem to have a hump-like structure on their backs; so it's not a stretch to suggest a species of that family could have developed a new structure (i.e. a sail)... Then again, we don't have enough spinosaurid material to restore with a good degree of confidence their evolutionary history, so it's all basically speculation.

[Zopteryx]

Here's my theory on how spinosaur sails evolved: 1) Megalosauroid genus in the Jurassic, like Dubreuillosaurus, have adapted to finding much of their prey in and around the water.  To keep their body temp up while in the water, elongated vertebral spines evolve to capture more heat. 2) These small sails/humps quickly become an attraction for the opposite sex and morph into a display function.  3) Some spinosaurs, like Spinosaurus, grow very large sails.  While still used for thermoregulation when in the water, the excessive size is primarily for display, either to members of its own species or competing species.

Basically, almost anything involving spinosaurs is speculation.  Like Sharptooth said, there's just not enough specimens.  Even the best known genera, Suchomimus and Baryonyx (which are very close relatives), are only known from one or two partial skeletons.  Spinosaurus is just known from isolated bones (many of which were destroyed in WW II), Irritator is known only from a skull, Oxalaia is kown only from a snout tip, Ichthyovenator is known only from a few vertebrae and other bones, and many other suppossed spinosaurs are only known from teeth and single bone fragments.  There's just not enough evidence to point either way at anything.

[darylj]

Great theory tho...  It makes good sense. Very good