Tuesday, July 4, 2017

Meathook Parade: Permutations, Iterations and Revelations On Predatory Theropod Forelimb Use

The following will be a blending of several under appreciated ideas on theropod forearm use combined with some of my own ideas. It seeks to drive at better answers by asking better questions.



Ahhh those theropod forelimb. They are a bit of an enigma, no? As bipedal primates descended from a brachiating pedigree of ape we have an intuitive awareness of our ability and utility to reach out and grab things.  Predatory theropods, despite being bipedal and equipped with arms and fingers like us, were a bit more constrained in their forelimb movements. The neck and head would be the first to contact with prey, the arms and claws being substantially rearward. Furthermore, the range of forearm extension and wrist movement was severely limited. Essentially the forearm and wrist acted as one single unit with the wrist unable to rotate and the radius and ulna locked together unable to rotate as well. The shoulder was likewise constrained to a relatively smal range of motion. Would it not have benefited predatory theropods to have freed up their forearms, wrists, and shoulders for a wider range of motion to assist in prey capture and manipulation? So that they could "reach out and grab stuff" like we do?

Suchomimus credit Duane Nash


Interestingly, there appears to have been at least one instance of theropods increasing both wrist and shoulder mobility and thus evolving the ability to "reach out and grab stuff" (Zanno et al., 2006). From wikipedia: "Within Therizinosauridae, broad changes to both the structure of the forelimb, pelvic, and pectoral girdles likely corresponded to changes in the lifestyle of the animals. The forelimb has undergone a drastic increase in robustness, the flexibility of the wrist has increased, and the presumed reach of the animal is believed to have lengthened. Moreover, the pectoral girdle has been modified to further augment upright reach, however the grasping ability of the animals is thought to have decreased. As with the modifications to the head, these adaptations are thought to have assisted with an herbivorous lifestyle, as they may have increased the ability to harvest and collect vegetation.[3]The obvious implication is that when the need arose to "reach out and grab things" the commensurate forelimb adaptations did arise - except that they did not arise in a predatory theropod but a likely herbivorous/omnivorous one!! Maybe the predatory theropod forelimb arsenal was not functionally adapted for "reaching and grabbing things" but served a separate purpose? Perhaps we are not satisfied with theropod forelimbs - that they are a bit enigmatic - because we are assuming the wrong job for them?

credit IsisMasshiro


There is currently a strong notion that whatever the forelimbs were doing - they were of secondary importance to what the head was doing in predatory theropods. And that if the hands were involved in prey capture they stabilized and held prey for the benefit of the head to deliver the dispatch. This notion is actually impractical for several reasons. Theropods neck musculature studies on Allosaurus indicate a design optimized to strike ventro-flexively (Snively et al, 2013). In other words they struck down and out away from the body. They were not optimized to strike back towards the body as would be expected if they bit into prey held in place by the arms. Furthermore the sheer implausibility of such a design is patently obvious when one tries to align the kinematics of such an action in the theropods with especially reduced forearms and short powerful necks such as tyrannosaurids and carcharodontosaurids.  Can anyone point me to one convincing depiction of short armed theropods holding prey with their arms as the bead bites into it?  It is also a bit of a myth that grasping hands are even necessary for the killing and dispatching of reluctant prey items by the mouth. Even a cursorary overview of both terrestrial and aquatic predators reveals that this is not the case - that the skull can be both a grasping and killing instrument - no hands need be involved.

Crylophosaurus credit Duane Nash


For this piece I am going to approach these "limitations" in wrist/arm/shoulder mobility from a different perspective. That these limitations were not at all limitations - they were in fact adaptive benefits. And that these benefits were not actually in place to assist in the capture of prey i.e. "the reaching out and grasping of prey", that was the job of the head. The forearms and wrists of predatory theropods were in fact so severely limited because of two, not mutually, exclusive reasons; 1)  many theropods would have dispatched prey with hand claws after the initial grasp by the jaws and 2) all predatory theropods - with notable exception of abelisaurids - would have used their forearms to transport food parcels to localized feeding locations and perhaps mates/offspring.

In other words it proves useful in flipping the equation: " the arms held prey for the head to dispatch" into " the head grabbed prey for the arms to dispatch" in order to understand the forearm use in a great many predatory theropods.

credit Brian Engh.

An important distinction that will color these arguments arose from an observation that Andrea Cau brought up to me in discussions on abelisaurids, theropods, and forearms. That there is a roughly inverse relationship between the power and bite of the head and the bulk and importance of the forearm in predatory endeavors. That is, for the theropods with weaker, slashing, and more modest skulls and teeth,  forearm strength and killing capacity are enhanced: spinosaurids, allosaurids, neovenatosaurids, megaraptors, basal tyrannosauroids, among others . Alternatively, where head power is enhanced arm strength and killing capacity is diminished: carcharodontosaurids, ceratosaurids, tyrannosaurids, abelisaurids. Now certainly this is not a hard and fast distinction, there were shades of grey, but I think it is a useful way to parcel out the discussion. No I am not saying that Suchomimus never killed with its mouth, nor am I saying that T. rex never killed anything in its hand claws. But they did invest in different arsenals and this should matter.
*Note that only in abelisaurids do we see the arms mutated into vestigial structures. This is an important distinction because even in theropods with reduced forearms they were not vestigial but offered an important functional usage in the transport and relocation of food resources. Dromaeosaurid forearm use will be discussed in a future piece.

In order to disabuse ourselves of the  notion of theropod forearms as tools for "reaching out and grabbing" or "holding onto prey for head dispatch" I want to revisit a term often used in the discussion of predatory theropod hand claws: meathooks. The term is a useful one, not only because it alludes to a human contrivance, but expresses quite succinctly the use of these forearms with due credit to notions of form and function having applicability not only in natural systems but culturally mediated systems of butchery. In both situations form follows function.

Megaraptor hand. author raffaeli serge CC2.0

Enough with all these academic pedantry I want to give you, the reader, an immersive feeling on what it was like to be young sauropod skewered alive on the Megaraptor meathook claws.





Ladies and gentlemen it is disturbing because the Mesozoic was disturbing - a real horror show. Now keep in mind the meathook claws of theropods, combined with a rather inflexible, strong, and stoutly built arm, work in conjunction to lock a food item in place. Such food items are pinned by either the opposing arm and claws or are wedged in against the torso. It is the meathook morphology of the claw combined with the limited range of motion of the arm and wrist that actually make escape from such a contraption very remote. In other words, the exact flaws that we have felt for so long are built into the system actually in this view are benefits. The prey can't squirm out of the arms due to the inherent inflexibility of the arms!!

credit Brian Engh used w/permission
Brian Engh (Don't Mess With Dinosaurs) did this evocative mural depicting speculative dinosaurs of the early Jurassic Navajo sand-stone of New Mexico. Brian made the rather atypical depiction of the putative top predatory holding a coelophysid in its claws. Also check out Brian Engh and other paleo goodies on July 13th 2017 at nerd night in L.A. if possible. I will try and make it too!!



There have been some detailed studies on large predatory forelimbs. One of the most interesting and little heralded studies is by Senter & Robins 2005. What I want to draw attention to in this abstract is; the extreme flexibility of the manus - the fingers can hyperextend; the permanently locked and bent elbow, unable to straighten; the notion of struggling prey further impaling itself on digit 1; and the noted difference between coelurosaur finger flexibility (they were doing different stuff) and other theropods .


What this study gets really right I believe is where they say "Acrocanthosaurus could manually grasp prey that was beneath its chest, towards which it may have used its mouth to move prey. Struggling prey would have impaled itself further upon the permanently and strongly flexed first ungual." Perfect, they really nail it here because they are the first - that I know of - to really decouple the forearms from the head as killing instruments in their own right. That is, it is not the claws holding the prey for the head to dispatch it is the head moving prey towards the claws for dispatch!! And this notion of the head deliberately moving prey items towards the killing hand claws does mesh well with the idea of sub equal sized prey items (i.e. loads of baby dinos) forming a heavy part of the diet of these animals. So while I am not the first to make this distinction - that the hands were killing implements independent of the head - I see no reason why this method can not be extended out to a whole range of other meathook handed theropods. Again, I'm not the first to advance this idea but I still maintain it has not garnered widespread exposure and knowledge.

The almost preternatural flexibility of some theropod fingers is something that does not get enough press. Once you look at the range of extension one has to wonder, why? The answer I would suggest is that the fingers took a lot of abuse from prey items squirming while engaged in the meathook bear hug. In order for the fingers to remain hooked in such flexibility would be paramount. No matter how hard and strongly the prey item squirmed the fingers would just flex and move to keep the hapless victim ensnared. Furthermore the basic function of an animal lifted off the ground and struggling against gravity would dictate that the claws dug in deeper to the animals; body cavities penetrated; lungs punctured; ribs cracking; viscera perforated; tendons gouged; and spinal integrity compromised. Abso-fucking-lutley brutal.

It is an ingenious solution: the fingers can bend and extend all over the place to absorb the struggles of the prey item, alternatively the extremely inflexible wrist, forearm, and shoulder maintain a rigid "meathook bear hug". Diabolical.

Probably the best visual I can find for the crazy hyper extendable meathook claws of some theropods is this visual from the recent study on Australovenator forelimb motion.





"I'll Show You the World" Australovenator credit Duane Nash



The megaraptoridae took this forearm dominance to the hilt, they also appear to show a bit more forward mobility in the shoulder joint perhaps even allowing food clenched in the hands to be brought up to the face - an unsettling manner of eating due to the similarity to our own feeding style.


credit Matt A. White, Phil R. Bell, Alex G. Cook, David G. Barnes,
Travis R. Tischler,Brant J. Bassam,David A. Elliott
Also of note is that by allowing the arms to engage in the killing activity the head - and most importantly the eyes - are safeguarded from retaliatory jabs of struggling prey. Many a prey item probably met their end after the initial grasp of the head in the clutches of the meathook bear hug. Trenchant hand claws - especially massive ungual one - dealing the death blow via grievous bodily insults much quickly and safely than injury incurred by the slashing teeth.

Of course I would be remiss to not give a mention to the several studies documenting abundant - and often extreme - forearm pathologies in predatory theropods (Senter & Juengst, 2016) in which a Dilophosaurus got absolutely wrecked, like freaking Monty Python style.

from Senter & Juengst. credit L. Walters (LWPaleoArt)
Senter & Juengst do a nice summary of documented forearm pathologies in theropods in the introduction - therefore saving me a load of work so I will put that here:

Some comments - a lot of mention of T. rex here. That might be a bit surprising considering T. rex should fall more into the "kill with mouth" gestalt. But there might be some reasons. As I will discuss later specific circumstances may have necessitated live prey being put in the arms of T. rex and other mouth dominant killers; the public, and researchers, like to obsess on T. rex so it might just be more looked over; multiple specimens; pathological features may often be omitted or overlooked in descriptions. Overlooked and omitted pathologies is interesting and Senter & Juengst go into some detail in these regards:

I should also give a mention to the work of Rothschild et al, 2001 that did some work on stress fractures and tendon avulsions in theropods as indicative of an active predatory lifestyle. I don't have the original work but it is heavily cited in the wikipedia articles on Ceratosaurus and Allosaurus both of which evince evidence of forearm and manus pathologies. Indeed the well documented trauma that Allosaurus sustained might be indicative of a willingness to sink its meathooks into prey substantially larger than itself!!

Earlier in this discussion I alluded to some of the reasons why a T. rex or other "mouth killing" theropods would have put a live or still struggling prey item in the grasp of its forearms. I also want to suggest some reasons why we should be optimistic about the utilitarian benefits of hauling parcels of food around in the arms (except for abelisaurids of course wink, wink). Let's remain mindful that as reduced as tyrannosaurid arms were, they were not vestigial. They were actually pretty damn powerful, conservative estimates give T. rex about 430 lbs on the bicep curl - a feat no human, not even pro-body builders can ever hope to achieve.

Removal of food from a highly competitive/dangerous arena to a more secure locale. Modern predators do it all the time. Hyenas haul off bits or whole carcasses. Raptors will take their prey off the ground to a safer location to eat. Leopards haul their kills up into trees. Carcasses can attract a lot of undue attention and if you have a way to move your larder to a more secure locale all the better for you.

*Note that, unlike quadrupedal predators that have to carry food in their mouth, theropods carrying food in their hands can still lash out and defend against would be usurpers with their mouth.



Transport of food to a mate and/or offspring. It is weird to think of such prosocial behavior in these animals but not without merit. Especially in light of the recent incubation lengths given for some dinosaurs - if such lengths were emblematic of theropods - then I think the discussion swings more and more into this realm.

Southern Ground Hornbill feeding mate. credit Steve Upton
Maximize exploitation of an abundant ephemeral food source. This is one of the funnest ones for speculative and humorous depictions. A bivouac of baby dinosaurs, a trapped pool of lungfish, a beach full of nesting/hatching sea turtles. Every once in a while predators get a gargantuan smorgasbord of easily acquired and abundant food stuffs and then it is gone. Theropods I would put forth as champions at taking advantage of these windfalls. First swallow as many as you can, then have each arm carry one, and finally cram as many into your maw as possible.

Greedy Daspleto credit Duane Nash


Atlantic Puffin w/sand eels credit Paul Mcllory CC2.0

So to review some of the main points:

- Predatory theropod forearm use has been stymied by our own intuitive understanding of having flexible, grasping forearms. We expect that theropods should have the same use of forearms in "reaching out and grabbing stuff" as we do, so that when we see they are limited in this regard it is thought of as an imperfect, problematic system.

- A study on the forearms of Acrocanthosaurus is one of the first mentions of theropod forearms being decoupled from the head as a killing mechanism in their own right. Forearm killing dominance has also been suggested for megaraptorids but can be extended out towards other theropods to varying degrees.

- There is a general pattern showcasing a trend from more mouth dominant predators to more arm dominant predators. Towards the extreme of forearm dominant predators would be spinosaurids and megaraptorids, towards the mouth dominant extreme would be tyrannosaurids and carcharodontosaurids.

- A meathook type claw morphology combined with a rigid arm anatomy would allow predatory theropods to not only kill but to carry prey/remains manually, useful for several very practical and not mutually exclusive reasons i.e. relocation of carcass, feeding of mates/offspring, hoarding of ephemeral rich food source.

- Forearm pathology in theropods is consistent with a heavy dependence on forearms in acts of predation.





References

Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.

Senter, Phil; Robins, James H. (2005). "Range of motion in the forelimb of the theropod dinosaur Acrocanthosaurus atokensis, and implications for predatory behaviour". Journal of Zoology266 (3): 307–318.doi:10.1017/S0952836905006989

  1. Snively, E., Cotton, J. R., Ridgely, R. & Witmer, L. M. Multibody dynamics model of head and neck function in Allosaurus (Dinosauria, Theropoda), Palaeontol. Elect. 16(2), 11A 29p (2013).


White MA, Bell PR, Cook AG, Barnes DG, Tischler TR, Bassam BJ, et al. (2015) Forearm Range of Motion in Australovenator wintonensis (Theropoda, Megaraptoridae). PLoS ONE 10(9): e0137709. https://doi.org/10.1371/journal.pone.0137709

Zanno, Lindsay E. (2006-01-01). "The Pectoral Girdle and Forelimb of the Primitive Therizinosauroid Falcarius utahensis (Theropoda, Maniraptora): Analyzing Evolutionary Trends within Therizinosauroidea". Journal of Vertebrate Paleontology26 (3): 636–650. JSTOR 4524610doi:10.1671/0272-4634(2006)26[636:tpgafo]2.0.co;2.









"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

Support me on Patreon.
Like antediluvian salad on facebook. Visit my other blog southlandbeaver.blogspot
Watch me on Deviantart @NashD1Subscribe to my youtube channel Duane Nash.



45 comments:

babehunter1324 said...

Some pretty interesting thoughts. And some really meme worthy images too :P

Bk Jeong said...

First of all: carrying a lot of food is a hilarious image.

Second: not sure if "slashing jaws" really means "hand-dominated killing". Your posts on Allosaurus really show what slicing teeth can do to prey, and even that's likely an underestimate of what slicing teeth can actually do. Predators in recent times with slicing bites (Smilodon, great white, Komodo dragon, etc) kill quickly if they need to (giant petrels killing slowly and gruesomely gets a pass, penguins can't fight back so they have no reason to hurry).

Anonymous said...

Could it be that maybe large scary arms were a result of competition with other theropods in the ecosystem, as defense?

Duane Nash said...

@Bk Jeong Well, yeah this post was all about the arms and claws. A different tactic used for different prey I would suggest. For Allo large prey I would lean more towards the head for multiple bites and retreats, for smaller prey the arms can kill quite quickly and at the same time help avoid dangerous retaliatory bites, pokes, strikes from the prey. Those claws are nasty - especially digit I - and they were doing something with them. If not reaching out and grabbing stuff perhaps killing things in their own right. Letting the arms do the killing helps get the face and most importantly the eyes out of range of damage. Even young sauropods were probably antagonistic prey. You had whip tails for some and macronarians could bite pretty hard. Not to mention many had thick hides and others osteoderms. Vicious hand claws could circumvent these defenses.

MrCrow said...

"The humerus can be retracted and elevated to subhorizontal positions and protracted somewhat beyond the vertical. In both taxa, the elbow can be strongly flexed but cannot be fully extended. Supination and pronation cannot occur by movement of the radius, which is immobile relative to the ulna. The palms therefore face medially except during wrist extension, which causes obligatory supination. The fingers of Deinonychus remain spread during flexion. In contrast, torsion of the distal articular surface of metacarpal I and the long axis of phalanx III-3 cause the first and third digits of Bambiraptor to approach each other during flexion, the first known instance of opposable fingers in a dinosaur" (Senter 2006). So, if the hands of Dromaeosaurs automatically supinate (rotate upwards) when the wrist is extended... perhaps that is an adaptation to carrying food as well? It surely had some sort of purpose..

Bk Jeong said...

I agree that young sauropods were still large and dangerous prey (and probably not that slow due to their stride length).

Lam Luong said...

I've seen Mapusaurus reconstructions with arm proportions even smaller than that in T. rex - I dare even say close to abelisaurid arm proportions - but they look functional like in other carcharodontosaurids. Do you have any takes on forelimb usage in Mapusaurus?

MrCrow said...

Hmm...juvenile Tyrannosaurids has proportionally longer arms...maybe they used their arms more than adults?

Duane Nash said...

@MrCrow good point about dromaesaur suppuration via that Senter paper. I've always been a little skeptical on that obligatory suppination part. I mean it does not really fall in line with the flight stroke? I'd like to see if there have been some challenges to it. But then again maybe its good. On juvenile tyrannosaurids longer arm being used more. Possibly, could be some evo-devo stuff going on as well as ecological/behavioral traits too.

@Lam Luong On Mapusaurus short arms (but still functional). Exactly, I would put them more in the kill with head, carry with arms camp. But again not suggesting that this is hard black/white distinction only that those large carchs seem to trend more in that direction. I would not be surprised that in Mapusaurus those arms were still quite powerful (like T. rex) and could probably haul large loads. T. rex is conservatively given a bicep loading strength of over 400 lbs. Scientists are notorious for low-balling these kinda things so when we take into account other muscle recruitment and the use of both arms I would not put the idea of lugging 1000 lbs of food to go for the combined use of both arms for a T. rex. That's a good sized meal, even for ol' rexy.

Κηφας said...

What do the cross sections of the various species' claws suggest? Like teeth, I would expect teardrop, narrow, or especially serrated claws to be cutting through things and therefore dispatching them, whereas round claws would seem more like meat hooks - going in and staying in rather than ripping through and out.

Maybe they were also used for holding onto large prey, to allow for repeated and/or glancing/raking bites?

Poppy Raima said...

While I'm inclined to agree with the idea of the arms of carnivorous theropods being much more functional that we give them credit for, I do have to notice that you essentially overlooked how these animals would actually be picking up a struggling prey item in the first place, particularly ones small enough to seemingly comfortably carry away in the arms like they're coming back from grocery shopping. (Great imagery, by the way.) Given the generally short and inflexible range of motion, how do you propose or envision that actually working? I can only picture stepping on such prey items to immobilize them, giving the predator time to actually bend forward or squat low enough to reach the quarry with its arms.

Duane Nash said...

@Knoac I have not heard of any serrated or cutting edge type hand claws for slicing, only the piercing raptor talon style that I know of.

@Poppy Raima " I do have to notice that you essentially overlooked how these animals would actually be picking up a struggling prey item in the first place"

Ummm, go read the post again. I say it like three or four times that the head brought the prey within reach of the claws. This is also the method mentioned in the Acrocanthosaurus paper I linked to. No reason that the feet could not pin prey for the arms to latch onto as you suggested, good point. Theropods, like birds had very flexible necks so even for the stouter necked types I could envisage this method.

MrCrow said...

Another use: Jacanas carry their young in their folded wings. So perhaps some Dinosaurs carried their young in their arms (wings in the case of Pennaraptorans).

Andrew Raymond Stuck said...

Wow, as interesting as your theories are, I don't always buy into them wholesale, but I think you may have really nailed it with this one, Duane. I've always thought it obvious that despite the pressure to reduce the size of theropod arms there was an equal pressure to eke every possible ounce of use out of them some way or another nonetheless. I simply couldn't figure out what that use might be given their range of motion. This hypothesis makes a stupid amount of sense.

khalil beiting said...

Great post! This makes perfect sense and I'd love to see more artists reconstructing this kind of behavior. I have always wondered why so many Theropods had massive and powerful arms yet are always envisioned to use the head. I also wondered why their arms were so powerful and big clawed yet had so little range and flexibility. But this summed it all up into a nice little bundle of badassery and evolutionary biology. I REALLY need to start drawing again so I can reconstruct all of these awesome behaviors and speculative appearances.

Anonymous said...

Sometimes I imagine Theropods and small ornithischians using their arms to help climb trees. Not necessarily that they were arboreal, but shuffling up a tree to get a better vantage point, to escape danger, to have a safe place to sleep, or to access a food item in the tree.

MrCrow said...

Sometimes I imagine Theropods and small ornithischians using their arms to help climb trees. Not necessarily that they were arboreal, but shuffling up a tree to get a better vantage point, to escape danger, to have a safe place to sleep, or to access a food item in the tree. (Sorry about double posting I just forgot to sign the last one with my name).

The Eurypterid said...

In regards to being used as killing claws, I'd note that the hypertrophied inner claw is shared by the marsupial lion, the only known mammal to probably use its limbs as a primary killing mechanism, in addition to the immediately-obvious deinonychosaurs.

Bk Jeong said...

The marsupial lions did have those claws, but it had f**king guillotines for molars. Seriously. That looks like a killing weapon.

Poppy Raima said...

@Duane Nash Okay, I misread part of it, my bad. I initially read that part as your disagreeing with the notion of a typical theropod being able to reach its mouth with it's hands and conflated it with the point where you mention the old theory of claw to mouth prey manipulation, but now I understand what you meant in that section. Regardless, more theropod arm involvement in paleoart is a good trend to move towards.

Tim said...

Great stuff Duane. Seriously, you should publish this 'meathook' idea. I think you've hit on something hugely important here.

I agree completely that the head (specifically the jaws) was the major predatory instrument in predatory theropods. The forelimbs were capable of surprisingly little reach and mobility. This is something many researchers have tended to overlook, due to our anthropocentric (and more generally primate-centric) view that arms and hands are for reaching out and grabbing stuff. But for theropods, the 'meathook' analogy fits the evidence much better.

Senter & Juengst (2016)'s study, which indeed shows that the forelimb of Dilophosaurus got "absolutely wrecked", is especially significant. The Dilophosaurus racked up a number of debilitating injuries in its forelimb - but it soldiered on. The authors state "During the healing period the ailments in their early states must have severely compromised the use of the forelimbs in prey capture. The survival of the animal despite these ailments therefore suggests a prolonged period of fasting or subsisting on prey small enough to be dispatched with the mouth and/or feet alone or with the use of only one forelimb." (Or maybe using no forelimbs at all...?)

The Senter & Juengst (2016) study emphasizes that the forelimbs were not critically important to Dilophosaurus' predatory strategy. The jaws could 'go it alone'. This would ordinarily be the case with small prey (as you say). This may be the case for many predatory theropods - the forelimbs had only an auxiliary function in predation, far inferior to the head. Yes, the forelimbs could help dispatch prey that was seized and held by the jaws, by locking prey in place and inflicting further injuries as it thrashed about. This would be especially true when the predator was dealing with relatively large prey. Many predatory theropods had forelimbs that were very robust and, but also quite short - including the spinosaurids (which were additionally equipped with a deadly thumb-claw) (e.g. Hone and Holtz's recent review.

Finally, in certain theropods, because the forelimbs had such a secondary role in predation, this might have 'freed up' the forelimbs for other purposes - particularly display.

SbS said...

Bone crushing or head dominant theropods with small less lethal arms might be proportional to the amount of competition.

Bone crushers like tyrannosaurs might have had so much competition that the relocation utility of carrying arms resulted into a reinvesting into the head so that it makes prey relocation obsolete. The bone crusher bypasses the need to carefully pick and clean their prey by sloppily eating everything.

Duane Nash said...

@Tim Thanks. Publication is something I have, well, "idiosyncratic" thoughts on. More on the modern peer reviewed paper business model forthcoming and how I think it can be dramatically improved and made over. That being said I'm glad you seem to have got most of the major points here.

@SbS On "tyrannosaurs" and "the bone crusher bypasses the need to carefully pick and clean their prey by sloppily eating everything." It is interesting that tyrannosaurids - supposedly the penultimate bone consumers - have the most elaborate adaptations to carefully nip and clean bone. They are the only theropods to have those "incisor" like front nippers D-shaped cross section front teeth after all. Funny how the other carnivorous theropods - which supposedly avoided bone at all cost - have no such adaptations to carefully avoid bone. Weird.

saeteren said...

The theropods' short and very little flexible forelimbs should indicate very well that they were secondary fligtless birds really, though more primitive than extant birds. I find it quite unrealistic or impossible that they should develop such forelimbs and other very distinct birdlike characters before they could actually fly. No extant ground dwelling creature other than birds have developed them.
I think all the dinosaurs were descendants of more or less developed birds really, where all of them used their forelimbs/wings actively in climbing/walking as well as in flying. If some used them only for gliding, their forelimbs would probably have been even less flexible and quite useless when they became exclusively ground dwellers. And a transition from gliding to active flight would probably be impossible, at least if they first used their forelimbs only for gliding. But I also doubt that a transition from climbing/walking to active flight for any of the limbs would be possible. Such limbs would't have a large enough bearing surface in the air, and their kind of movement wouldn't be suitable.
I think the evolution of birds has been a very long process that started already with the first diapsids. They were probably tree dwellers, and may already have had a kind of wings when they first came up on land from the water, maybe not so unlike those of rays, of which some can actually also make a "flapping flight" in the air. They probably used their "limbs" both for a kind of climbing and flight right from the start. They must first somehow have "flown" up into the trees I think, for otherwise they would hardly have developed flight at all.
And I think that also all the reptiles have evolved from these forms at different stages of flight development, hence they more or less share similar characters with birds as well as with the prehistoric flying lizards/Pterosaurs.

Duane Nash said...

Is that you Josh Jackson? The second coming of BCF? Well I'm not going to stop you from having your opinion, I don't see a lot of evidence of early theropods showcasing secondarily flightless characteristics. But this is not the topic for this post and there is quite a lot of thought on this subject in various invocations of the birds came first scenario both online and in various writings by Josh Jackson. It had a certain appeal back in the 90's but I don't think the evidence that has came to light in recent years bears it out. Best, Duane

Tim said...

An arboreal/climbing origin of dinosaurs is science fiction. As Duane points out, there was a flurry of interest in the 1990's in this "birds-came-first" idea - but it's now utterly defunct. All dinosaurs, including theropods, were thoroughly terrestrial with a parasagittal gait. Its only in the bird lineage (avialans) that we see indications of real scansoriality/arboreality.

The short forelimbs of theropods are NOT a consequence of secondary flightlessness. It's due to bipedality. Bipedality, which is primitive/plesiomorphic for Dinosauria, is likely a consequence of the shift to cursoriality - see Persons & Currie (2017). The forelimbs of theropods were probably not used to seize/apprehend prey. I think Duane has made a good case for their actual function, as tools that aided the predator to subdue prey held in the jaws.

saeteren said...

No, I'm not Josh Jackson, I have actually not heard of him before.
Since secondary flightless theropods is not the topic for this post, I shall not persist on this discussion. I will just mention Scansoriopteryx, which is found to be more primitive than the theropods and the dinosaurs as a whole. But nevertheless it must have been a kind of bird, for it had f. ex. feathers, and even flight feathers on its wings it seems. It could evidently climb trees, and I'm sure it was also capable of active flight. It resembled very much the maniraptorans I have understood, and may therefore have been a precursor to them. This should indicate that at least the maniraptorans was decendants of climbing and even flying forms. And some maniraptorans which earlier was thought to be developing into birds, are now found to actually have been capable of flight.

khalil beiting said...

@saetereb who on Earth has proclaimed Scansoriopteryx more basal than Theropoda, let alone Dinosauria!? This has nothing to do with the post and you sound insane to think that Theropoda or god forbid Dinosauria come from flighted ancestors. Where are you even getting this stuff from? You sound even worse than *shudders* David Peters. Seriously, where are you getting this from because nobody in recent DECADES has said or mentioned ANY of that stuff in a serious tone.

"Since secondary flightless theropods is not the topic for this post, I shall not persist on this discussion."
>continues to ramble on

saeteren said...

I have read about an examination of Scansoriopteryx, wich was done with the help of quite advanced aquipment made by Alan Feducia and Stephen Czerkas some 3 years ago. I'm no expert in these matters, so I can't right away tell you what methods. They found that Scansoriopteryx did not have some traits that is common for all the dinosaurs, but rather more basal and primitive traits. If you really are ignorant of this, I am surprised.

Duane Nash said...

@saeteren Again this post is not about bird origins or Scansoriopteryx so it is a little more than annoying to me that you insist on hijacking this comment section. I too am no expert on avian origins but I know enough to know that the work of Stephen Czerkas (RIP a great sculptor & paleoartist BTW) and Feducia has been fairly soundly and thoroughly shredded. For years they and their ilk rejected maniraptorans as bird relatives, then when they finally had to capitulate to that loss they said that maniraptorans are not dinosaurs they just show convergence. They ignore cladistic completely and invent their own definition of dinosauria to fit their hypothesis. This is a clear example of changing the goal posts and shoehorning the data to fit your hypothesis which is bad science. If you really are ignorant of this, I am surprised.

Here's a good start:https://qilong.wordpress.com/2014/07/10/really-again-youve-got-to-be-fucking-kidding-me/

Surely if you read my posts to any measure you are well aware that I often go against what might be considered "general consensus" or "mainstream" views. I'm certainly not averse to new ideas or challenges to paradigms. But this whole debacle is one that doesn't cut the mustard.

Again, this is way off topic there are loads of people online way more versed in the ins and outs of why Feducia & Czerkas need to give it up who I'm sure can illuminate you further but I consider the matter closed as it pertains to this comment thread and will delete further comments on the subject - not because I am trying to silence you - simply because it is distracting from my time, off topic, and thoroughly rebutted elsewhere.

Best, Duane

saeteren said...

Duane. I'm sorry to have insisted on hijacking this comment section, but I just had to answer khalil beiting when he asked me from where I had got the stuff about Scanseriopteryx.
You're talking about Czerkas and Feduccia's shoehorning of data to fit their own hypothesis, but this can certainly also be said about the other side of the conflict. I will only mention the fact that most maniraptoran fossils are younger than Archaeopteryx, which is explained by Archaeopteryx' descending from unknown older maniraptorans.
Czerkas, Feduccia and their like may have been wrong in their assumption that maniraptorans were not bird relatives. But they have at least been willing to correct themselves, and have come to what is likely the wright view, that maniraptorans decended from volant birds, and were therefore birds themselves.
I have less confidence in those who never change or correct their own view, very likely because they are afraid a loss of prestige.

Tim said...

Re theropod forelimbs... another thing to consider is that there is strong evidence that the hands of maniraptorans might have been functionally didactyl. In Anchiornis, the second and third fingers were bound together by skin, as preserved integument shows (Wang et al., 2017). This would seem to rule out a climbing/grasping function for the manus. Based on skeletal evidence, previous work has suggested that the same (2nd + 3rd fingers bound together) might have been true for other theropods, including Archaeopteryx (Mayr et al., 2007), Chirostenotes (Currie & Russell, 1988), and Struthiomimus (Nicholls & Russell, 1985)

I wonder if this configuration might be typical of all theropods - including the predatory theropods mentioned here. In theropods with a tridactyl manus, were the 2nd and 3rd fingers bound together, with only the first finger ('thumb') free and mobile? If so, it might undermine your interpretation that "the fingers can bend and extend all over the place to absorb the struggles of the prey item". Then again, this feature (2nd and 3rd fingers bound together) might be limited to coelurosaurs, or even just to a subset of paravians.

Duane Nash said...

@Tim I did seek to spotlight that this is not referring to maniraptoran forelimbs as I do think that they were doing things a bit differently. If you the abstract to the acrocanthosaurus paper it states that there is a distinction between the way the forelimbs of carnosauran theropods work versus maniraptoran. Also that paper was the first time I had come across the hyper extendable finger observation. I suspect that the 2nd and 3rd fingers of maniraptorans are bound together in skin is because many are potentially secondarily flightless or at least were almost flighted at some point. In other words I don't think that trait is a basal plesiomorphic trait for all theropods.

That is the first time I have heard the idea of Struthiomimus having the 2nd and 3rd fingers bound together. That paper is a little old though and I have not read it.

Tim said...

@Duane Re Struthiomimus, the quote from Nicholls and Russell (1985) is "The incipient coalescence of digits II and III, and their ability to be
strongly flexed suggests that they were enclosed in a common sheath of
skin". (So their interpretation is somewhat speculative.) Note that if ornithomimid forelimbs sported large feathers (Zelenitsky et al., 2012; although Foth et al. 2014 were more skeptical), it might be consistent with a more maniraptoran-like manus.

I agree that maniraptorans should be considered distinct from other theropods - I was interested in your thoughts regarding the possibility of fingers being bound together elsewhere among theropods. I think there's a high probability that critters like Anchiornis, Microraptor, and Archaeopteryx were capable of powered flight (probably launching 'ground-up') - this might well explain why two fingers were bound up in integument. I highly doubt these critters could climb trees ('ground-up' flight would make climbing unnecessary anyway).

MrCrow said...

@Tim, "I highly doubt these critters could climb trees" keep in mind that crocodiles aren't built for climbing trees yet they can climb. Also Microraptor at least occasionally hunted tree dwelling Enanthiornithines (http://www.pnas.org/content/108/49/19662.full).

Tim said...

@MrCrow
Crocodiles have a low center of mass and sprawling posture, which makes them predisposed to scansoriality. This is true for a lot of extant reptiles. It is not true for dinosaurs, including birds.

Re Microraptor hunting tree-dwelling (arboreal) enantiornithines... The fact that Microraptor ate arboreal birds does not necessarily indicate that Microraptor climbed trees. It is possible Microraptor flew up into the tree to seize arboreal birds (PeerJ 4:e2159 doi.org/10.7717/peerj.2159). Or, maybe Microraptor hunted the enantiornithine bird on the ground. A Microraptor was found with fish remains in its guts (Evolution doi: 10.1111/evo.12119). This suggests Microraptor "appears to have been an opportunistic and generalist feeder".

MrCrow said...

@Tim good points.

MrCrow said...

New SVP abstracts (http://vertpaleo.org/Annual-Meeting/Annual-Meeting-Home/SVP-2017-program-book.aspx) including upcoming studies on theropod forelimbs, Dromaeosaur pedal claw function, and the development of bird beaks. Things you've talked about here on this blog.

Duane Nash said...

Thanks for heads up MrCrow, I spent my day off yesterday perusing it. And yes several of the topics are of some relevance to things I have discussed here. Lots of interesting ankylosaur stuff too. Not going to go this year however due to several other things going on, wedding etc etc.

saeteren said...

If microraptor really ate fish, it should have been capable of powered flight, if it didn't just jump down on the fish from a tree. And it may also have been able to dive under water to catch the fish, like diving birds of today.

Regarding the theropods' forelimbs again, I don't think that any of them used them for predation, but only for locomotion. Their ancestors probably used their clawed wings for climbing trees, and I imagine that at least the big carnosaurs used their forelimbs in about the same manner in shallow waters. For I think that these, like also the big sauropods, were aquatic cratures. They were simply too big and heavy to be competetive for a life on dry land, and especially as they were bipedal. I image that the largest carnosaurs's great weight made it necessary for the forelimbs to be held approximately straight down through shallow waters, or when they needed to crawl up on land, in order for them to lift up and push the body forward. This may explain the relatively very short forelimbs of the largest carnosaurs, like f. ex. the Tyrannosaurs.
At least some maniraptorans may also have been aquatic or partly so, and maybe some of them still occasionally climbed trees. I understand that at least some, if not all maniraptorans had their second and third fingers bound together with skin. Couldn't it be that this was a part of a still remaining wing membrane, like that of Pterosaurs? And couldn't it still be possible to use those fingers in climbing? Maybe the maniraptorans and their ancesters also had some shared traits with Pterosaurs, as well as with the birds.

Duane Nash said...

OK saeteren I don't know where to start with all of this, so i won't. I don't know if you are just a kid, have aspergers, are trolling or whatever BUT just about everything you brought up can be easily dismissed with some rather cursory investigation even just wikipedia.

So please start there!! You should know form this blog that I'm sympathetic to out of the box ideas but I'm sorry the things you are bringing up are just reheated garbage from yesteryear. They don't cut the mustard in the least.

And please no one else follow up with this it will just encourage.

Hey sorry if I'm coming off dickish but so be it. I don't have the time to correct every error in your thinking/ideas and I've warned you once to not hijack and to stay on topic. If you can't stay on topic and keep bringing up ideas that are easily dismissed (or have been dismissed numerous times in the past) you will find yourself B-A-N-N-E-D just like a couple of other knuckleheads are. Don't be a knucklehead sauteren. Maybe just watch from the sidelines, stay quiet and learn. There is nothing wrong with that. Realize that hey this isn't my first rodeo - I've trashed a lot of mine own ideas - and I was well into my 30's before I started coming up with better stuff.

saeteren said...

Duane, your response just show how single-minded and almost dogmatic this science have become, and I guess you are a pleontolog yourself. When someone comes up with alternating ideas about evolution, they are being bullied and almost banned, like the pope church once banned heretics. If you have come to a point were you are not willing to reconsider your own picture of ideas any more, you are not a true scientist really. You are just following the main stream, probably very much because you are afraid of becoming a heretic.

I have of course after all to accept that your perceptions doesn't conform with mine, but I can't accept that you again are accusing me for not staying on topic. Wasn't the theropods' forlimbs and the use of them exactly the topic of this post? And in this respect, it should be allowed to present the hypothetical background for this.

MrCrow said...

Mr.Nash, I have since learned that we are not allowed to publicly discuss on social media the unpublished SVP abstracts. I hope you don't mind me asking this, but could you please delete that comment? I don't want to cause any trouble.

The Wolf of Comedy said...

So if I understand correctly, certain theropods could have used their forearms to dispatch of small prey animals instead of using their jaws?

Duane Nash said...

yup

Related Posts Plugin for WordPress, Blogger...