Thread: Spinosaurus Jaws and Diet Discussion

Spinosaurus was a genus of megalosauroid theropod dinosaur that lived during the Middle Cretaceous in what is now North Africa. Based on its snout and tooth morphology alike, we can infer than spinosaurus, like all spinosaurids in general, was primarily piscivorous by nature. Its snout was very thin and specialized, perfect for quickly snatching up fish in water with minimal water resistance (drag). That being said, its snout was actually very robust, as it was very dense (it lacked the impressively-sized fenestrae present in animals with considerably lighter-built rostra, such as carcharodontosaurus, which is evident below. Compared to allosauroids, which killed vertically and possessed exceptionally deep rostra, spinosaurus killed by gripping, which means that its snout as a whole would have to be imperatively strong, as it lacked in any exceptional depth or width), and its post-premaxillary rostrum in general was very heavily-buit and was much more generalized opposed to the very specialized tip which was clearly too gracile in build to be used in macro-predation and was instead designed to hook fish.

Regardless of width, we can safely acknowledge that spinosaurus was at least characterized by jaws that would have faired much better for gripping and resisting lateral forces than carcharodontosaurus (as carcharodontosaurus had a much deeper rostrum relative to width, telling us that it was certainly not very resistant to these kinds of forces) and modern piscivorous crocodilians. A study has even been published regarding multidirectional loads on the skulls of 5 different animals: Spinosaurus Aegyptiacus, Baryonyx Walkerii, American alligator, Indian gharial, and African slender-snouted crocodile. Surprisingly, spinosaurus actually did worse than all of these animals in lateral resistance. Although the main issues with this is that they supposedly used a reasonably more gracile spinosaurus specimen (the largest spinosaurus specimens have very robust rostra in general and were clearly more generalized. Specimens like this include MSNM and MNHM), and they only put the premaxilla area into account for spinosaurus (that area was considerably more gracile than the rest of its rostrum, specifically the area posterior to that, which was a good deal more broadened). Compared to the slender-snouted crocodile and similar piscivorous species, spinosaurus had a much more heavily-constructed central and rear-most rostrum, which means that this area was fundamentally more robust in general and would have been a good deal more resistant than the more specialized region proceeding it.

Spinosaurus clearly had a very powerfully-built post-premaxilla rostrum and mandible alike. Its rostrum, despite lacking in both exceptional width and depth, was still very robustly-built and very dense, making resistance a smaller issue here than many claim. The tests did not account for the region posterior to the specialized premaxilla area of the spinosaurus' rostrum, which means that the full potential of the rostrum's ability to withstand lateral stress was never reached. The majority of spinosaurus' rostrum was very heavily-built and strong, despite being thin in multiple directions. In the event that spinosaurus would be hunting a large terrestrial animal, the more generalized region posterior to its specialized cleft region would most likely be used to bite down, as that area would have the least chance of breaking and the total biting force would be a good deal higher. Spinosaurus would most likely not use its specialized foremost region of its snout in macro-predation, as that area was designed for specialized piscivory.

Mr. Godzillasaurus, tear down this wall!

...of text and properly format it to facilitate discussion.

Spinosaurus dentition is also a good deal underrated in many peoples' eyes. People always claim spinosaurus to have been much less deadly than carnosaurs or tyrannosaurids because their teeth were conical and unserrated as opposed to laterally compressed (although only slightly in tyrannosaurids) and the possession of functional carinae (they were very ill-adapted for cutting). That is not true at all. The teeth of spinosaurus, while still being very elongate and lacking carinae, were still very thick and very robust, more than capable of withstanding good amounts of both lateral and vertical stress alike.

In addition, its dentition was, as I said, very elongate and relatively slender. This in conjunction with their conical shape and lack of serrations is an indicator that spinosaurus was very adept at piercing deeply into the hide of a prey animal (as it was a very successful piscivore) and causing a good deal of internal damage under the right circumstances.That being said, spinosaurus still lacked an exceptionally powerful bite (again, evidenced by its narrow yet robust rostrum and mandible) unlike that of tyrannosaurids (which had particularly wider rostrums and mandibles alike). Because of this, we can use the impressive resistance of its snout to tell ourselves that spinosaurus would have killed large terrestrial animals (basically, smaller dinosaurs) by clamping onto them with the central region of its snout and violently shaking its head up and down to cause good amounts of spine-related puncture/stress damage or doing so with very precise bites (as its teeth were obviously designed to pierce deeply. Theropod on World of Animals convinced me of this tactic). Its teeth were very robust and spike-like in themselves, but they were merely designed for gripping as opposed to causing fatal spinal or flesh wounds, so spinosaurus would have had to kill animals in different ways than something like tyrannosaurus or carcharodontosaurus.

But that being said, they would have been very deadly in the event that spinosaurus managed to grab a hold of a prey animal or was very precise in he delivery of a deep impaction of the spinal cord. In this case, its dentition would be able to easily cause a good amount of spine-related or internal neck damage due to its very specialized morphology. As I said earlier, spinosaurus would have not killed using the cleft regions in both is dentary and premaxilla, as those areas were very specialized and would have likely been broken very easily. It would instead utilize its more robust region posterior to its premaxilla.

Originally Posted by Flick Montana

Mr. Godzillasaurus, tear down this wall!...of text and properly format it to facilitate discussion.

Got it. I just fixed it

Thats a LOT of text to have to sift through to be honest.

What are you looking specifically do discuss?

(Also Binomials should be capitalized genus name and lower case species name, all in italics: Spinosaurus aegyptiacus and Baryonyx walkerii rather then "Spinosaurus Aegyptiacus" and "Baryonyx Walkerii")

Semi-aquatic (shallows, really) is pretty certain from its posture and balance. Spinosaurus would be clumsy on land, but neither a fast swimmer with those limbs hanging useless. Safe to assume any fish it failed to snap by chance, spinosaurus had no hope of pursuing?

Could have pounced up at shoreline prey very well though. See, a pounce that overshoots a bit has those large claws seizing prey, then the slender neck (for this function) may crook around allowing Spiney to bite any protruding part with the side of its jaws, while still holding the prey. It doesn't have to get out of the water and stand on its food. And obviously Spiney can't perform a death-roll. So does this resolve the problem of reducing a carcass to pieces it can swallow?

I'm thinking that with smaller prey, spinosaurus could have employed a quick snap in any direction with that longish neck. This attack is not slowed by the inertia of its body. That would be true ambush behaviour - just wait for smaller prey to come within range of a sudden bite.

As for the teeth. I don't know much about them but is it not likely spinosaurus would sometimes in its life snap down hard on a turtle shell? Just biting whatever brushed by, you know. Fancy teeth aren't worth their fine points if you'll accidentally break them. I'm suggesting the plain conical teeth may have just been insurance against abuse, not shaped like that for any specific purpose.

Clumsy on land? It has the same overall body plan as the rest of the theropods did, and the vast majority of them are all though to have been active predators.

Please tell me that the conclusive fight between a Spinoaur and Tyrranosaur from Jurassic Park 3 encouraged you to post this...

Originally Posted by Paleoichneum

Clumsy on land? It has the same overall body plan as the rest of the theropods did, and the vast majority of them are all though to have been active predators.

Overall body plan, like hominids share the same overall plan so should be equally bipedal.

Forelimbs don't support the weight, so terrestrially it must balance at the hip. So far so good. But note the shorter and lighter counterbalance tail, plus the additional weight of the "sail", which may have been a fatty hump. Could you build a standing model that doesn't tip over?

Besides other reasons to conclude this animal was more adapted to water.

What are you looking specifically do discuss?

The diet of spinosaurus.

As for the teeth. I don't know much about them but is it not likely spinosaurus would sometimes in its life snap down hard on a turtle shell? Just biting whatever brushed by, you know. Fancy teeth aren't worth their fine points if you'll accidentally break them. I'm suggesting the plain conical teeth may have just been insurance against abuse, not shaped like that for any specific purpose.

Actually, spinosaurus' teeth were very specialized. As I have said earlier, they were very slender (or elongate) and very well adapted for piercing deeply without much effort. That combined with their overall robusticity and resistance (they were actually particularly strong and were more than capable of withstanding large amounts of pressure) implies that large and powerful fish made up most of its diet. Its teeth were very well constructed for piercing into the hides of large fish and retaining a strong grip. So yes, they were in fact very specialized.

Please tell me that the conclusive fight between a Spinoaur and Tyrranosaur from Jurassic Park 3 encouraged you to post this..

.

Definitely not...

Originally Posted by Pong

Originally Posted by Paleoichneum

Clumsy on land? It has the same overall body plan as the rest of the theropods did, and the vast majority of them are all though to have been active predators.

Overall body plan, like hominids share the same overall plan so should be equally bipedal.

Forelimbs don't support the weight, so terrestrially it must balance at the hip. So far so good. But note the shorter and lighter counterbalance tail, plus the additional weight of the "sail", which may have been a fatty hump. Could you build a standing model that doesn't tip over?

Besides other reasons to conclude this animal was more adapted to water.

yes actually, multiple models have been constructed.

What researchers suggest a fatty hump on the spines?

What other reasons?

Originally Posted by shlunka

Please tell me that the conclusive fight between a Spinoaur and Tyrranosaur from Jurassic Park 3 encouraged you to post this...

Do you know where my mobile phone is by any chance..../tic :-))

Originally Posted by Implicate Order

Originally Posted by shlunka

Please tell me that the conclusive fight between a Spinoaur and Tyrranosaur from Jurassic Park 3 encouraged you to post this...

Do you know where my mobile phone is by any chance..../tic :-))

I'll call it from the landline if you don't find it. Only have text credit on mine for now.

Originally Posted by moonmule

Originally Posted by Implicate Order

Originally Posted by shlunka

Please tell me that the conclusive fight between a Spinoaur and Tyrranosaur from Jurassic Park 3 encouraged you to post this...

Do you know where my mobile phone is by any chance..../tic :-))

I'll call it from the landline if you don't find it. Only have text credit on mine for now.

Moon, that was a quote from the movie JP3......

Originally Posted by Paleoichneum

Originally Posted by Pong

Could you build a standing model that doesn't tip over?

yes actually, multiple models have been constructed.

With steel posts in a concrete base, or cables from the ceiling. Okay, that's unfair. I'll take your word there are models of the animal free-standing and balanced, and I'd very much like to see them. To my eye, looking at the skeleton, Spiney seems way front-heavy in contrast to classic terrestrials like T Rex.

Originally Posted by Paleoichneum

What researchers suggest a fatty hump on the spines?

The guy who first described the fossil, for starters. Second paragraph on wikipedia. I assume it a reasonable hypothesis.

Originally Posted by Paleoichneum

Originally Posted by Pong

Besides other reasons to conclude this animal was more adapted to water.

What other reasons?

It ate fish.


Now I feel a flight of fancy coming on, bear with me.

I suggest spinosaurus employed two very distinct modes of catching and eating prey.

One mode was passive ambush predation. In water, either fully submerged or surfaced, the animal would simply conserve energy and wait for small fast prey - like fish - to come within striking range of its head. In striking, spinosaurus neither thrust forward nor moved it's body much - that is too slow against small prey. Rather it whipped its head sideways to catch prey at eye level. It could afford to fail in most of these attempts because it wouldn't go chasing through the murk after its food. Many modern reptiles employ this cost-saving strategy, including crocodiles of course. Crocs make the strike by suddenly clinching their bodies into a "C" so the head swings around, but a spinosaur's longish neck alone could propel a quick strike. That's more akin to the snapping turtle, with an extended-neck strike capability all around its otherwise docile body.

An entirely different mode of predation targeted larger prey at the water's edge. On detecting the (usually terrestrial) prey spinosaurus would creep toward it, fairly hidden by water or vegetation. In range, the difference lies in the strike: because spinosaurus can't effectively seize prey with a face-on bite, it used the talons. This requires pouncing with the whole body. So, kick off from pond-bottom and lunge up, claws spread. The jaws have no role in this. With successful strike the prey is gripped and probably dragged down, away from land. At this stage spinosaurus may begin eating/killing its prey by biting any part that sticks out, like a limb. Like I suggested earlier, spinosaurus needs a means of tearing large carcasses into pieces it can swallow. Holding a carcass with the forelimbs while twisting away with the teeth should work fine, because the flexible neck allows that.



JP3, didn't see that. Did Rex conquer to triumphal music?

Holding a carcass with the forelimbs while twisting away with the teeth should work fine, because the flexible neck allows that.

This depends on what part of its snout it would be using. It would most likely not use the particularly gracile and specialized foremost region of its snout, as that area was only used for fishing purposes and was horribly adapted for dealing with large terrestrial animals. In this case, the theropod would most likely use the more robust central region of its snout over anything when it comes to tearing.

And even then, more forceful means of separating flesh would need to be put into place, as spinosaurus' teeth did not work in the same way as those of many other carnivores like allosaurus or carcharodontosaurus; they were very elongate and conical, and they lacked serrations. Spinosaurus' teeth were used mainly for puncturing into the hides of fish (gripping, fundamentally) so such ripping would likely need to be done more forcefully, such as by head-shaking. But that being said, head shaking would be very risky when using the specialized premaxilla of its rostrum and it could only really be done efficiently and to prevent injury with the robust central and posterior region of its rostrum. And even then, its snout was designed to be very strong when gripping large fish, not necessarily with dismemberment and/or such shaking.

I agree the snout's a liability if closed on large prey that is fighting back. But if Spiney's MO against these was to drag down with the forelimbs, well a drowned dinosaur doesn't struggle! In terms of behaviour, I suppose a simple inhibitory instinct against biting things that are large and struggling, would protect that snout from accident.

So, large prey stops twitching. Now how to eat it? At this stage Spiney's still holding the body down with its claws, but its inhibition against biting is subsiding. Why not try some gingerly nibbles into the soft spots? If that produces nothing to swallow, Spiney can grip some skin with its teeth and pull back. The stress on its jaws is minor, since this is tension running straight back to the neck. It can repeat this simple yanking action until it's worked an opening into the meat and gore.

Crocs can't do anything like that, as they lack a means of holding their food in place, and lack a neck with which to pull back while biting. I think it's been said that groups of crocs performing death-rolls on a carcass "cooperate" by twisting in opposition. But a lone crocodile rolling over and over with its food doing likewise, demonstrates the worst method of eating possible.