Theropod non-locomotory limb function

[Godzillasaurus]

Oh wait, looks like I looked at the image wrong. There IS in fact a humerus there, my mistake

[theropod]

Jun 14, 2014 2:35:32 GMT 5 Godzillasaurus said:

But yes, I do remember people favoring it over deinosuchus, an animal that not only possessed far better weaponry for taking down the opposer but was also squat and armored.

Considering the average size of Deinosuchus rugosus, less than 3t, I can understand them very well. The crocodilian’s weaponery would surely have faced considerable problems bringing down an animal twice its weight. Either way therizinosaur vs crocodilian is a faceoff that is very difficult to imagine and that would surely be very difficult for both of them.

It get that, but would they necessarily be designed for using powerful
swipes to create broad wounds? For example, bears and giant sloths
possess(ed) very robust forearms that were quite ideal for this, and
polar bears especially use them to bring seals and such onto land. Not
to mention their claws are better designed for that

Therizinosaurus’ arms were at least as robust and powerful as bears’. In terms of the claws, they are difficult to compare, polar bear claws are more akin to cat claws in that they are curved and sharp afaik, but brown bear claws are longer and streighter, but blunt. As I wrote, therizinosaur claws were something unique, a mixture of features. All I can say is that these features make it seem very realistic that they could be used as lethal weapons.

In species that utilized their jaws as their primary weapons (ie.
tyrannosaurids, megalosaurids, allosaurs, etc), the forearms most
definitely served the sole purpose of assisting in grappling prey; I
agree with that. But their shape is simply much better designed for
slashing than a straighter, longer, and more slender claw.

It is not, that’s like saying a meathook is better suited for slashing than a steakknife. these where grappling hooks, and they were optimized for that purpose. Therizinosaurus’ claws are completely different. Maybe they were used for swiping, maybe for stabbing in some way, but in any case a robust, rounded, curved claw is not useful for slashing.

I realize that 1. there would have been a keratinous covering in life,
and 2. it would have increased their strength overall. BUT, while the
laterally-compressed shape is present, are they the best designed for
any real slashing?

Yes, one would expect so. At least claws that are not compressed and have rather rounded profiles can hardly be good at it.

 I don't think so. It is possible that, while the claws and forearms
were the primary weapons of therizinosaurids (quite obvious actually),
defense may have only been a secondary function.

Secondary function or not (which would not rule out a use in confrontations and thus primary design for fighting), their mechanical aspects are not unsuited for being used as a really serious weapon.

It is downright possible that their enlarged design was merely to assist
in feeding (by possibly allowing the creature to "bring down" tall tree
limbs possibly; I have read about this theory before).

This theory makes no sense for two reasons:

• If they where used to bring down branches, why the hell are they so straight and compressed, and not strongly hooked and blunt?
• it is beyond unlikely that it could raise its hands further than its head to effectively grasp or pull something, considering the likely lenght of its neck.

I beg to differ. Those were only the forearms, so naturally they would
appear much thicker proportionally than more complete skeletal arms.
Pantherines and bears both do not necessarily possess the most gracile
forelimbs:

Humeri are known for Therizinosaurus, and the link I included showed the complete arms.
Unsurprisingly even fairly robust forelimb skeletons can look gracile is you compare them to forelimbs with flesh, skin and fur on them. The problem is, you are using either those or other giant theropods as a comparison, and the latter often have forelimbs that are just insanely robust (related to their purpose, which was not killing stuff or slashing at anything).
But that alone may not be so important, since lenght, reach and flexibility are also very important factors as to how it could use them as an actual weapon. Again, it must have used them very differently from other theropods.

True, but the effectiveness would likely differ. Remember, positioning
is also key here, and stegosaur thagomizers were positioned perfectly
for deep penetration (which would have likely been very crippling if it
struck a predator in the thigh for example), while it seems rather
"awkward" to think that therizinosaurus and its closest kin would
deliberately jab at opponents (or at least to the point at being as
effective)

Awkwardness is not the point, any animal with claws that big will of course look awkward to the human eye, regardless of what it does. It also seems rather awkward to me that the speed you move at affects the speed you experience time in, but hey, it is a scientific theory! In this case, it is much simpler and less awkward.

They certainly had the capability for swiping and potentially creating
"surface" scratches, but I doubt they would have been as effective as
the fore claws of many other groups of theropods and felids in that they
were not heavily hooked and were not particularly broad.

Being heavily hooked is an adaption for grasping, not killing, and being narrow is an advantage for slashing.
Neither felids nore most other groups of theropods used their claws as their primary (killing) weapons, much more they need grappling tools, which is the primary use of their claws. These hooked claws of course have good penetrating ability, but they are not the only conceivable shape, and perhaps not the best, for being used as a weapon.

Without a doubt the claws were their primary weapons, but weapon
effectiveness depends on positioning as well instead of just size. I
would not wager that its arm/claw combination would have fared well if a
predator (such as tarbosaurus) were to bite them or simply run in to
ram it. They were certainly weapons, but they did not seem to be the
most effective as opposed to stegosaurids, whose enlarged and elongated
thagomizers were not only designed perfectly but also positioned
correctly in a muscular and probably very powerful tail.

There are no reasons to presume that Therizinosaur forelimbs where not also very muscular and powerful, and what they lacked in this regard they could probably have made up for by dexterity and precision. It is hardly possible two types of weapons that are so different on a morphological and evolutionary basis where used in exactly the same way, but that one was an effective and lethal defensive weapon still lends support to the hypothesis that the other was too.

[creature386]

I just read some hypotheses on Therizinosaurus' claw function in The Dinosauria on page 163. Wow, some really seem to believe that such a large animal could use the claws for feeding on insects. However, I got an interesting thought. Maybe some dinosaurs buried their eggs in mound like nests and Therizinosaurus could have used its claws to open them, similarly to how an ant eater (also elongate claws) opens termite mound. Or maybe it opened the lairs of some mammals like this. I don't believe this was the only function, just thinking of whether the often used ant eater analogy can maybe be applied when using something larger than insects.

[theropod]

I could think of numerous ways those claws could have been used.
Perhaps they where some sort of biological machete, helpful for feeding and when the animal moved through dense vegetation.
Maybe they where some sort of shovel or rake, or really used for cracking insect mounds (the latter makes more sense in smaller therizinosaurs though imo, it does not really explain the extreme size in T. cheloniformis).
However all of these explanations would allow for them to be used as defensive weapons.

Merely the claws being used to pull down branches into feeding range however doesn’t make any sense to me, as it would require extreme hyperelevation (so extreme that we can’t assume it was capable of it) to even reach as far as its own head, and then the claws would have a shape very poorly suited to hook and pull.

[creature386]

Jun 14, 2014 15:35:03 GMT 5 theropod said:

Maybe they where some sort of shovel or rake, or really used for cracking insect mounds (the latter makes more sense in smaller therizinosaurs though imo, it does not really explain the extreme size in T. cheloniformis[/i[)

Yeah, that's why I tried to replace insects, like cited in The Dinosauria, with something bigger.
Some other theories cited in that book are really crazy though, like a segnosaur hanging from the trees like a sloth.

[Infinity Blade]

Jun 14, 2014 15:08:25 GMT 5 creature386 said:

I just read some hypotheses on Therizinosaurus' claw function in The Dinosauria on page 163. Wow, some really seem to believe that such a large animal could use the claws for feeding on insects. However, I got an interesting thought. Maybe some dinosaurs buried their eggs in mound like nests and Therizinosaurus could have used its claws to open them, similarly to how an ant eater (also elongate claws) opens termite mound. Or maybe it opened the lairs of some mammals like this. I don't believe this was the only function, just thinking of whether the often used ant eater analogy can maybe be applied when using something larger than insects.

I'm not sure if Therizinosaurus would want to eat eggs and/or mammals (as those theories seem to imply it wants to eat them).

[creature386]

This is assuming that it was omnivorous. If the insect eater theory is considered serious, why not this? And after all, we have no evidence for it being an obligate herbivore. In fact, all the evidence for its food preferences come from phylogeny.

[Infinity Blade]

I could very well say the same for it being an omnivore. Going from close relatives, it being a herbivore is the most likely, no?

[creature386]

What I mean is given that we don't know what it ate, we cannot falsify that the claws were used to open mounds/nests/lairs by saying it was a herbivore. The reason is simply that grasping branches doesn't make so much sense (claw shape wise), while ant eater claws are also very elongate. The only thing that would hide in the structures I mentioned are animals or their eggs.
I am not sure if we actually know whether its relatives were complete herbivores either.

[Godzillasaurus]

Considering the average size of Deinosuchus rugosus, less than 3t, I can understand them very well. The crocodilian’s weaponery would surely have faced considerable problems bringing down an animal twice its weight. Either way therizinosaur vs crocodilian is a faceoff that is very difficult to imagine and that would surely be very difficult for both of them.

But the theropod's weaponry was massively sufficient, especially when considering its opponent

Therizinosaurus’ arms were at least as robust and powerful as bears’. In terms of the claws, they are difficult to compare, polar bear claws are more akin to cat claws in that they are curved and sharp afaik, but brown bear claws are longer and streighter, but blunt. As I wrote, therizinosaur claws were something unique, a mixture of features. All I can say is that these features make it seem very realistic that they could be used as lethal weapons.

For lethal swiping to cause nasty broadened wounds, it seems notoriously unlikely. Shorter, recurved claws simply tend to be much more effective weapons than supposedly rather heavy elongated and straightened claws. I wouldn't hold my breath that they were as lethal as you think, but that is just me

It is not, that’s like saying a meathook is better suited for slashing than a steakknife. these where grappling hooks, and they were optimized for that purpose. Therizinosaurus’ claws are completely different. Maybe they were used for swiping, maybe for stabbing in some way, but in any case a robust, rounded, curved claw is not useful for slashing.

A steakknife is sharply-edged and serrated; therizinosaur claws were not. If they were optimized to have been used that way, then it seems probable that they would at least be designed for such. Curved claws can definitely be used as weapons, simply because their hooked shape and sharp points would allow for effective slashing given enough driving force. It is as simple as that. If therizinosaurus' claws were designed for such slashing, it would be beneficial for them to have been shorter and more strongly recurved (simply because their realistic morphology is awfully flimsy and would likely cause the structure to break)

Yes, one would expect so. At least claws that are not compressed and have rather rounded profiles can hardly be good at it.

If they were much shorter, than it is possible. Longer, straighter, and more slender structures tend to be far from efficient at any sort of forceful tearing and slashing, regardless of cross-section shape. If a claw is particularly (at least somewhat) narrow but yet sharp and recurved at the same time, it would prevent breaking all that much more and would thus make slashing far more effective than a structure that was probably too fragile for such a job, even if the primary function of the latter was gripping.

Secondary function or not (which would not rule out a use in confrontations and thus primary design for fighting), their mechanical aspects are not unsuited for being used as a really serious weapon.

They were definitely deadly, but they seemed far too flimsy and fragile to be quite a deadly as you seem to be implying

Humeri are known for Therizinosaurus, and the link I included showed the complete arms.

This is already realized by me. I examined the arms closer and actually saw traces of humeri as opposed to just the forearms and hands (I justified this in my previous post here)

Being heavily hooked is an adaption for grasping, not killing, and being narrow is an advantage for slashing

To say the least, if therizinosaurus possessed much shorter and broadened (laterally) claws, then I would agree that slashing would be the primary function. But you still must realize that, aside from being laterally-compressed, there really is not much else to back up this theory.

Neither felids nore most other groups of theropods used their claws as their primary (killing) weapons, much more they need grappling tools, which is the primary use of their claws. These hooked claws of course have good penetrating ability, but they are not the only conceivable shape, and perhaps not the best, for being used as a weapon.

I realize this, but a shorter and recurved claw would nonetheless be more resistant to fracturing than one that was much longer, more slender, and erect; regardless of if that said claw's primary function is for grappling prey.

I'm not sure if Therizinosaurus would want to eat eggs and/or mammals (as those theories seem to imply it wants to eat them).

In terms of carnivorous behavior, I see insects as the primary food source. Although therizinosaurids were most likely primarily herbivorous, I would not disagree that insects at least could have played a part in diet.

I remember I once saw a clip from a documentary (I forget which one) where a therizinosaurus actually ate a tarbosaurus hatchling... And it played the "role" of the "villain"... My initial reaction was one big FACEPALM

[creature386]

From what I know, this documentary is simply called "Tarbosaurus".

[theropod]

For lethal swiping to cause nasty broadened wounds, it seems notoriously unlikely. Shorter, recurved claws simply tend to be much more effective weapons than supposedly rather heavy elongated and straightened claws.

Which would be exactly the specifications of most bears’ and many xenarthrans’ claws…

You have not explained why a morphology that actually corresponds to gripping (the "shorter recurved claws" as seen in most other theropods) is iyo superior in causing damage than this claw shape.
In fact, cassowaries have straight claws, which they evidently→ _{(download warning)} use as deadly weapons. Bears have notoriously powerful paws, even though they have at times been overhyped, and anteater claws are also elongated, but still very powerful instruments capable→of killing a human→, there are even anecdotes of them killing jaguars.

Curved claws can be very dangerous weapons, but by no means does that mean straighter ones aren’t as well. The curved design primarily aids in gripping, it’s not important for dealing damage. And there is more than one single way for an animal to use its claws to kill something!

A steakknife is sharply-edged and serrated; therizinosaur claws were not. If they were optimized to have been used that way, then it seems probable that they would at least be designed for such.

Well, for some reason no claws in the animal kingdom seem to be serrated, not even the sharpest ones. And even if they were, the bony core would likely not preserve any trace of it.
Selective pressure on a claw is a different thing from selective pressure on a tooth, their orientation is different and so is their size and strenght.

Curved claws can definitely be used as weapons, simply because their hooked shape and sharp points would allow for effective slashing given enough driving force. It is as simple as that. If therizinosaurus' claws were designed for such slashing, it would be beneficial for them to have been shorter and more strongly recurved (simply because their realistic morphology is awfully flimsy and would likely cause the structure to break)

As you will see, your assumptions base on a premise that you lack evidence for.

The majority of animals with curved claws (mostly theropods) certainly did and do not use them for slashing, which is the reason for those claws being round or oval in crosssection–the exception being cats, but their claw’s primary function is still gripping, and accordingly their morphology is not ideal to cause deep slash wounds, rather they are built to cut into the skin to get a good grip.

If a claw is particularly (at least somewhat) narrow but yet sharp and recurved at the same time, it would prevent breaking all that much more and would thus make slashing far more effective than a structure that was probably too fragile for such a job, even if the primary function of the latter was gripping.

You seem to be of the erraneous assumption that therizinosaur claws were particularly "flimsy" and fragile, while they actually are not. The claws of dromaeosaurs and accipitrids are slender as well, your eyes are deceiving you. the difference is that they are curved, which makes the whole structure seem more compact, without the claw itself actually being thicker.

If they were much shorter, than it is possible. Longer, straighter, and more slender structures tend to be far from efficient at any sort of forceful tearing and slashing, regardless of cross-section shape.

And why if I may ask?

If a claw is particularly (at least somewhat) narrow but yet sharp and recurved at the same time, it would prevent breaking all that much more and would thus make slashing far more effective than a structure that was probably too fragile for such a job, even if the primary function of the latter was gripping.

But most theropod claws are not narrow and sharp, they are rounded and robust. The very point is that this shape is designed for robusticity, not slashing. In a claw made for slashing, one could realistically expect the opposite morphology, although I think thether they are recurved or straightened is rather irrelevant.

[ultimatedinoking95]

I love theropods, and I have often wondered at the function of their hands, from what I've read, they could not rotate their wrists due to the radius and ulna being locked together. but the arms must have had some use, for the Spinosaurs, they may have been used as fish hooks, small theropods may have used them to grab tiny prey, and Dromeosaurs may have used their arms to hang onto larger animals, so they could stab them with the sickle-claws. as for Carnotaurus, those stumps are a mystery, too small to be of any real use, they couldn't reach a mate, scratch an itch farther than a few inches, and had almost nonexistent claws. given a few million years, they may have been lost completely, as in the Moa.

[theropod]

It is quite obvious abelisaurid forelimbs could not possibly have served a function in hunting, due to the extreme reduction of the antebrachium, manus, or claws. However I wouldn’t go so far as to conclude they were useless alltogether.
Their robust shape actually makes complete vestigialism no more likely than it is for tyrannosaurids (despite them being even less raptorial in built).

Burch & Carrano 2012 said:

Although the forelimb is highly reduced distally, abelisaurids retain large scapulocoracoids with broad areas for muscle attachment and a robust humeral morphology. The hemispherical humeral head would have allowed an extensive range ofmotion at the shoulder, potentially less restricted than in typical theropods.

Mating claspers actually sounds like a good use they could put those things to. In fact, the extreme reduction of the distal parts makes sense for a greatly reduced structure with single specialized function without requirement for a lot of flexibility or dexterity.

The extreme shortness of the manual elements, especially in Majungasaurus, makes it unlikely that the individual digits retained much autonomy, and it is possible that the manus was employed as a functional unit.

both from here→

Tyrannosaurid forelimbs are built differently from abelisaurid ones, but I’m fairly confident they’d be capable of serving similar actions.

What they have in common is considerable amounts of strenght and resistance.

I find the thought of tyrannosaurs as well as abelisaurs using their forelimbs to aid in rearing up (Stevens et al 2008) and that as mating claspers the most compelling, as they would both explain their short lenght, the ocurrence of occasional stress fractures and their robusticity and strenght. Note that both do not require a lot of reach or flexibility. All that it
would take would be to stay in place to stabilise the animal on a mate
or on the ground.
In tyrannosaurs, I can also see an occasional use on prey or opponents, after getting in a bite of course. This would be rather rare and unimportant behaviour though.

[Infinity Blade]

How strong do you think megalosauroid and carnosaur forelimbs would have been compared to those carnivorous mammals?