Recurved, serrated teeth in baryonychines: why?

[Godzillasaurus]

This is one question that I have always asked myself: why did baryonychines possess more typical theropod dentition among the more unusual conical dentition of spinosaurines? It is obvious in terms of snout and forearm anatomy that baryonychines were of course piscivores (they in fact had proportionally more narrow snouts than spinosaurines), but then what is the purpose of the recurved and serrated dentition better structured for tearing? I have never actually found the answer to this question. Is it possible that they wold have hunted fish in a completely different way opposed to the typical simple grabbing method of spinosaurus and its closest kin?

[creature386]

Narrow snouts can also be used for small terrestrial animals, killing them with quick slashing bites. If anything, a broader snout helps more with fish, given how much the large ones struggle.

[Derdadort]

Maybe Spinosaurins are simply more derived than Baryonychins and therefore the "primitive" teeth in Baryonyx etc.?
Additionaly we have evidence that both, Spinosaurins and Baryonychins, fed on both fishes and terrestrial animals.

[Godzillasaurus]

May 27, 2014 22:22:23 GMT 5 creature386 said:

Narrow snouts can also be used for small terrestrial animals, killing them with quick slashing bites. If anything, a broader snout helps more with fish, given how much the large ones struggle.

Well fundamentally a broad snout is not necessarily ideal for piscivory, as the thin shape of spinosaurid jaws allows quick and easy maneuverability in water (as opposed to something broadened, which would cause too much drag, at least if used vertically). But yes, in this case, spinosaurus' jaws, being relatively similar to those of the false gharial in general, seem to indicate that it was in fact an opportunist that would have taken large fish for the most part.

And spinosaurus' rostrum too was even less pneumatic and gracile than that of baryonyx, at least basing off of the fenestrae size (in which case spinosaurus had very few openings aside from the nares in its actual rostrum itself) and it seems that the nares in baryonyx were not forced upward as we see in spinosaurus:



Undoubtedly there still are parallels with spinosaurus such as the obviously very shallow and narrow snout in general and presence of a "hooked" premaxilla. Both of these are heavy indicators that it would have fed mainly on smaller animals, but the specifics are unknown (although we do have evidence of iguanadon remains in a baryonyx stomach cavity, so at least we know that it too was an opportunist feeder). We know for a fact at least that spinosaurus was PERFECTLY adapted for hunting large fish, if its dental and snout morphology along with its raised nares is already enough. 

[theropod]

I’m agreed with Derdadort. Baryonychines represent a more plesiomorphic morphology than spinosaurines (compare their tooth morphology to the oldest known spinosaur, Ostafrikasaurus, to get an idea), hence their deeper, narrower snout and recurved, serrated dentition, which are more consiostent with typical theropods. Nevertheless both groups are already very specialized and different from norma theropods.

Baryonychines simply represent a more "primitive" branch of spinosaur than spinosaurines do. Unsurprisingly, spinosaurines are typically younger in geological terms, with most baryonychines being from the Valanginian-Aptian while most spinosaurines are Albian-Cenomanian in age (with a few exceptions of course).

Godzillasaurus: The raised nares are problematic as an argument, because the position of the naris on the fossil doesn’t necessarily reflect the position the fleshy nostril had in the living animal (Witmer 2001→).

I think regarding the drag the difference is neglegible, and if anything dependant on the direction the animal most often moves its snout in when striking fish. Crocodiles mainly use sideways motions for catching fish, but a taller animal like a theropod will have to strike from above, so we cannot realistically expect the same snout shape, even if it served the same purpose.

[Godzillasaurus]

Crocodilians with dorsally thin snouts are still, however, best designed for tackling fish either way you slice it. Although the broader snouts of species lil the American alligator for example can be used for lateral swiping in water to catch fish, that snout shape is undoubtedly the least ideal for piscivory among crocodilians. Of course alligators do catch fish regularly (fish make up the majority of their diet, at least in juveniles), but a thinner snout shape and sharper teeth do make for better fishing tools altogether.

But as for the phylogeny aspect of spinosaurids, I can definitely see the primitive features in baryonychines more reminiscent of those of the megalosaurids such as more-so pneumatic rostra and serrated tearing dentition, as they might have simply not evolved the more advanced and specialized features of spinosaurus (ie. finely-pointed conical teeth). But the upped nares would definitely be an ideal characteristic for such an animal (one that hunts fish from up above), as they would allow the creature to breathe while hunting. I also read someone's theory that spinosaurus could have been an efficient scavenger given the slender snout and nostril positions, and scavenging would certainly make sense at least part of the time given the creature's immense size (here is the article in question: whenpigsfly-returns.blogspot.com/2008/01/feeding-adaptations-and-strategies-of.html)

[theropod]

Yes, that’s because fluid dynamics are a rather complex matter. There is both pressure and viscous drag involved in the overall drag a structure creates, and of course as thin and small in every direction as possible is the best way to reduce both components as much as possible

Still, all extant crocodilians have proportionally wider snouts, and they generally strike fish with transverse movements, so the form drag appears to be the predominant selective pressure.

But the upped nares would definitely be an ideal characteristic for such an animal (one that hunts fish from up above), as they would allow the creature to breathe while hunting.

One would expect so, but with nares in particular we sometimes see odd developments. For example, why do diplodocids have those huge nares high on their heads when their actual nostrils were on their snouts just like most other animal’s?

As regards kleptoparasitic behaviour in Spinosaurus, it does make a lot of sense for it to behave that way. However carcass dismemberment certainly wasn’t its area of expertise, while others were (its teeth are neither well-suited for tearing not are its jaws well-suited for bone-crushing, while they are just perfect to catch fish and well-suited for many small to mid-sized prey items), suggesting that despite its ecological capability to do so, this wasn’t more important for it than for other predators.

[Godzillasaurus]

Still, all extant crocodilians have proportionally wider snouts, and they generally strike fish with transverse movements, so the form drag appears to be the predominant selective pressure.

Aside from the Indian gharial, which was not particularly robust at all. And still, the differences in width for spinosaurus and tomistoma (in general) would still be negligible. There is no denying that the two genera were similar in this regard for the most part (aside from immensely robust specimens of the latter, but yet we still barely have anything to work with for the former), and both were possibly similar ecologically

One would expect so, but with nares in particular we sometimes see odd developments. For example, why do diplodocids have those huge nares high on their heads when their actual nostrils were on their snouts just like most other animal’s?

But would it not make complete sense? If spinosaurines attacked fish from above the water, it would be a perfect evolutionary feature. Compare and contrast it to modern cetaceans, which evolved nares practically on top of the head for more efficient breathing.

And I perfectly agree that it was a fish hunter for the most part; there really is no denying it unless you consider it too weak to tackle large fish (which it obviously wasn't). Just that the scavenging theory was attributed to its (at least potentially) raised nares

[theropod]

Spinosaurus is not comparable to a cetacean, it was completely capable of terrestrial weight support and locomotion for all we know. Do herons have their snouts in the water all the time while catching fish? I don't think so. How do you know Spinosaurus did, because planet dinosaur showed it like that? The facts are, we don't really know.

If anything, I would envision it having just its lower jaw in the water anyway, at least most of the time, since it would want to have its mouth already open (unless you think it used those jaws for suction feeding, which seems rather unlikely to me considering the relatively small volume) as well as reduce drag as much as possible.

In a scavenger, one would not expect a long snout, conical teeth and nares that are set high, rather one would expect brevirostry and crushing or ripping teeth. It strikes me as highly unlikely, that, whatever the real position of its nostrils, it had more to do with adaptions for scavenging as the rest of its morphology--nothing.

PS: with proportionally wider snouts I was referring to width/depth, not width/lenght. I.e. flatter rostra.

[Godzillasaurus]

Spinosaurus is not comparable to a cetacean, it was completely capable of terrestrial weight support and locomotion for all we know. Do herons have their snouts in the water all the time while catching fish? I don't think so. How do you know Spinosaurus did, because planet dinosaur showed it like that? The facts are, we don't really know.

I know that. It was just an analogy: why would cetaceans ever evolve raised sinuses? Because it is an ideal adaptation for their exclusively aquatic lifestyle while still being air-breathers. I meant "compare and contrast" in the sense that raised nares would be ideal for both groups of animals; not necessarily saying that they were alike.

If anything, I would envision it having just its lower jaw in the water anyway, at least most of the time, since it would want to have its mouth already open (unless you think it used those jaws for suction feeding, which seems rather unlikely to me considering the relatively small volume) as well as reduce drag as much as possible.

Spinosaurus likely did not hunt with its mouth agape waiting for fish to swim within striking distance. As you said, its jaws were of little volume (at least compared to more typical theropods) and were designed for drag reduction. If it lied in wait as such, it seems likely that its snout be much wider (and shallower, much like laganosuchus, which was the perfect prehistoric example of this. Even some species of modern crocodiles do this at areas of rushing water) and its teeth be much smaller and more numerous. It would also be attacking from up above (more perpendicular), not parallel to the water like modern crocodilians do (as it was a biped). I do not know if this is a proven idea or not, but this is my theory, so you can feel free to object.

In a scavenger, one would not expect a long snout, conical teeth and nares that are set high, rather one would expect brevirostry and crushing or ripping teeth. It strikes me as highly unlikely, that, whatever the real position of its nostrils, it had more to do with adaptions for scavenging as the rest of its morphology--nothing.

I do agree that scavenger behavior is not fully conceivable, at least primarily. It was an evolved piscivore; I do already get that piece of it, but he did make an interesting assumption that it would help the creature to avoid injury, and its slender skull would be ideal for going deep into a carcass (also note its large size and spinal column, which could have been used for intimidation purposes). Its snout and tooth morphology does correlate best with that of piscivorous ecology, but again, scavenging is entirely possible, at least part of the time (possibly if fish are scarce)

[creature386]

Jun 6, 2014 1:51:19 GMT 5 Godzillasaurus said:

If anything, I would envision it having just its lower jaw in the water anyway, at least most of the time, since it would want to have its mouth already open (unless you think it used those jaws for suction feeding, which seems rather unlikely to me considering the relatively small volume) as well as reduce drag as much as possible.

Spinosaurus likely did not hunt with its mouth agape waiting for fish to swim within striking distance. As you said, its jaws were of little volume (at least compared to more typical theropods) and were designed for drag reduction. If it lied in wait as such, it seems likely that its snout be much wider (and shallower, much like laganosuchus, which was the perfect prehistoric example of this. Even some species of modern crocodiles do this at areas of rushing water) and its teeth be much smaller and more numerous. It would also be attacking from up above (more perpendicular), not parallel to the water like modern crocodilians do (as it was a biped). I do not know if this is a proven idea or not, but this is my theory, so you can feel free to object.

But there are crocodile species without the adaptations you have listed (many small teeth, broad snout) yet they still lie and wait. Given that various shapes work for the typical crocodilian lifestyle, I don't see why it shouldn't work for Spinosaurus.

[theropod]

Godzillasaurus: I was not saying scavenging behaviour was not likely for Spinosaurus–because from an ecological perspective it is highly likely. It is just that its functional morphology does not correlate with it, i.e. it was not adapted to do it. Animals often do stuff they are not really adapted for anatomically, even when they are rather ill-suited for it, as long as it is somehow possible.

Spinosaurus likely did not hunt with its mouth agape waiting for fish to swim within striking distance. As you said, its jaws were of little volume (at least compared to more typical theropods) and were designed for drag reduction. If it lied in wait as such, it seems likely that its snout be much wider (and shallower, much like laganosuchus, which was the perfect prehistoric example of this. Even some species of modern crocodiles do this at areas of rushing water) and its teeth be much smaller and more numerous. It would also be attacking from up above (more perpendicular), not parallel to the water like modern crocodilians do (as it was a biped). I do not know if this is a proven idea or not, but this is my theory, so you can feel free to object.

The problem with Laganosuchus (whose jaws aren’t particularly broad btw) as an analogy is the difference in positioning. A crocodile would not be able to strike fish from above, even if it wanted to, simply due to its low stance.
Also, points like tooth size and snout width are fundamentally different among the two groups (we both already elaborated on that), as you already pointed out. their predation strategy is not really comparable.

I was rather thinking of certain piscivorous birds (namely Rhynchops). Of couse Spinosaurus would not fly above the water and sweeping it until its mandible touched a fish, but it must have had its body and head above the waterline while fishing, so it too would almost necessarily attack its prey from above. The two also share the trait of a very deep mandible (unlike crocodilian mandibles wich are very shallow).

When opening its mouth far enough to catch a sizeable fish (especially in shallow, swampy water), it could automatically result in only the mandible remaining submerged. So it would make sense to adopt this behaviour alltogether while lurking for prey, as it would likely be quicker, more economical and anatomically easier to accomplish.

I think it would have varied its fishing methods somewhere between a stork and a skimmer, depending on the prey and the setting. I just didn’t find the "closed mouth held underwater-theory" very convincing. Firstly, as I already wrote, its nostrils are no proof of that. Secondly, such behaviour would only make sense if it employed suction feeding–needless to say that would only work with very small fish considering the small volume of its jaw apparatus (and THAT would really throw up the question why it had such large teeth, robust mandible and an uneven toothrow-profile).

[Godzillasaurus]

Godzillasaurus: I was not saying scavenging behaviour was not likely for Spinosaurus–because from an ecological perspective it is highly likely. It is just that its functional morphology does not correlate with it, i.e. it was not adapted to do it. Animals often do stuff they are not really adapted for anatomically, even when they are rather ill-suited for it, as long as it is somehow possible.

I understand this. This was my point; if spinosaurus was large enough for intimidation purposes, scavenging is possible if fish were to ever become scarce from any sort of environmental reason. Crocodiles have been known to venture onto land to get to a carcass, and they for the most part are hunters:



Even if it was in the end scared away, it still exhibited typical scavenging behavior.

The problem with Laganosuchus (whose jaws aren’t particularly broad btw) as an analogy is the difference in positioning.

They were broadened but yet very shallow, which is why the creature was dubbed "pancake croc":

A crocodile would not be able to strike fish from above, even if it wanted to, simply due to its low stance

Which makes it logical why spinosaurus would have evolved a proportionally deeper snout, because that allows for greater vertical resistance, and raised nares. Crocodilian snouts are "upturned" for a lack of better words at the tip, mainly because they are primarily aquatic quadrupeds with very short legs (they will ambush larger prey such as deer by "disguising" themselves as logs, and in this sense, it is imperative that they would be able to breath while swimming on the surface of the water).

I was rather thinking of certain piscivorous birds (namely Rhynchops). Of couse Spinosaurus would not fly above the water and sweeping it until its mandible touched a fish, but it must have had its body and head above the waterline while fishing, so it too would almost necessarily attack its prey from above. The two also share the trait of a very deep mandible (unlike crocodilian mandibles wich are very shallow).

Which again seems to be why its snout as a whole was deepened. If it were attacking a fish, it would undoubtedly need to breathe (where then its bipedal stance and supposedly raised nares correlate). We discussed how it would pull a (probably very large) fish out of the water pretty much vertically. Simply, attacking from above would make raised nares an ideal adaptation to compensate for its lifestyle of vertical grabbing as opposed to being pretty much parallel with the water's surface.

When opening its mouth far enough to catch a sizeable fish (especially in shallow, swampy water), it could automatically result in only the mandible remaining submerged. So it would make sense to adopt this behaviour alltogether while lurking for prey, as it would likely be quicker, more economical and anatomically easier to accomplish.

Or in the case of it coming from above, its snout would enter the water almost perpendicularly. It is definitely possible that it killed in the same fashion that you are talking about, but the "sitting and waiting with mouth agape" theory seems illogical considering its morphology.

I think it would have varied its fishing methods somewhere between a stork and a skimmer, depending on the prey and the setting. I just didn’t find the "closed mouth held underwater-theory" very convincing. Firstly, as I already wrote, its nostrils are no proof of that. Secondly, such behaviour would only make sense if it employed suction feeding–needless to say that would only work with very small fish considering the small volume of its jaw apparatus (and THAT would really throw up the question why it had such large teeth, robust mandible and an uneven toothrow-profile).

Which is why it most likely caught prey quickly and powerfully. Its teeth were designed for deep pentration while its snout was very narrow but yet deeper than those of all modern crocodilians (at least proportionally). Coming from up above is probably the most logical theory as to how it hunted. But even if it did strike perpendicular to the water, in no way would its teeth be the only structures securing the fish in its mouth: it would need to motion its snout outward, so the relevance of the lower jaw still is present here.

[theropod]

Godzillasaurus: I know about Laganosuchus aka "pancake croc", I have had a look at its description. What I was saying was that its snout is not particularly broad at all. Broader than Spinosaurus’ snout of course, like most crocodilians, and broader than gharials’ due to its distinct, rounded shape. But in relative terms, not broader than most other crocs’.
My point was that I don’t think the functional morphology and hunting method of pancake croc were in any way comparable to spinosaurs. In fact, the two seem to be on opposite sides of the scope as far as the morphometrics and lifestyle of a specialized piscivore can go.

Which again seems to be why its snout as a whole was deepened. If it were attacking a fish, it would undoubtedly need to breathe (where then its bipedal stance and supposedly raised nares correlate). We discussed how it would pull a (probably very large) fish out of the water pretty much vertically. Simply, attacking from above would make raised nares an ideal adaptation to compensate for its lifestyle of vertical grabbing as opposed to being pretty much parallel with the water's surface.

The point was that it didn’t necessarily have its upper jaw in the water anyway.
Even with a conservative gape angle of less than 50%, it could reach in way deeper by just abducting its mandible than by sticking its whole snout in as deep as possible, and the former eliminates the need for extreme head ventroflexion (something that would put a lot of strain on its nuchal ligaments).
Here, for a little visual demonstration:

full-sized version→

Of course the way it held its skull would also depend on the type of fish and the depth, but in moderately deep water and with moderately large fish, it makes most sense for it to have its rostrum almost parallell to the surface and its mandible depressed. That way its mouth would already be opened and facing forward to catch whatever fish it wanted to catch, all it had to do is shut its mouth by cranial depression and mandibular adduction.
This would also make sense for baryonychines.

[Godzillasaurus]

Godzillasaurus: I know about Laganosuchus aka "pancake croc", I have had a look at its description. What I was saying was that its snout is not particularly broad at all. Broader than Spinosaurus’ snout of course, like most crocodilians, and broader than gharials’ due to its distinct, rounded shape. But in relative terms, not broader than most other crocs’.

It doesn't have to be: it was still far different from that of spinosaurus, and was perfectly designed for lying in wait to catch smaller and weaker fish

My point was that I don’t think the functional morphology and hunting method of pancake croc were in any way comparable to spinosaurs. In fact, the two seem to be on opposite sides of the scope as far as the morphometrics and lifestyle of a specialized piscivore can go.

I firmly agree with this

Even with a conservative gape angle of less than 50%, it could reach in way deeper by just abducting its mandible than by sticking its whole snout in as deep as possible, and the former eliminates the need for extreme head ventroflexion (something that would put a lot of strain on its nuchal ligaments).

I don't believe I ever said that it would go in at a 90 degree angle every time, did I? Just that it would likely not have its snout parallel with the water when closed, like a crocodile.

Of course the way it held its skull would also depend on the type of fish and the depth, but in moderately deep water and with moderately large fish, it makes most sense for it to have its rostrum almost parallell to the surface and its mandible depressed. That way its mouth would already be opened and facing forward to catch whatever fish it wanted to catch, all it had to do is shut its mouth by cranial depression and mandibular adduction.
This would also make sense for baryonychines.

But would this be the most efficient and effective way to catch fish? Remember, it would be striking from above. I am really bad at physics though. But of course, it nonetheless was adapted for pulling fish out of the water from above, both morphologically and stance-wise. It was similar to a few crocodilian species in terms of feeding apparata, but it was still not a squat quadruped