@@DevinDTV Well you have to understand that most of the muscle in the shoulder area of a T. rex is dedicated to the neck and jaw. Many large carnivorous Theropods developed along these lines, to the point that Carnotaurus only has little nublets for arms that are way more vestigial looking that T. rexes.
Was the arm more balanced when the T-Rex was younger? Every dinosaur had to start from the size of an egg, and maybe it played a role in the child/adolescent stage of the T-Rex's life?
@@christopherellis2663 Differing proportions over life stages is extremely common in nature. humans for one, we have proportionally larger heads as infants than as adults, we also grow additional molars as we mature. In almost all insects major morphological changes occur from egg to adult. Most extreme being the endopterygota which undergo complete metamorphosis. If we’re talking about the concept of maintaining juvenile features into adulthood, the phenomenon, called neoteny is pretty widespread. The axolotl being a prime example. In terms of maintaining structures which only serve a function in immature organisms there are examples of this as well, the belly button is a good one.
@@christopherellis2663 lots of different places within the animal kingdom, juveniles having a different lifestyle and by extension different anatomy is fairly common among animals.
The problem with this idea is that there is muscle scarring on adult T-Rex skeletons. Muscles are kind of use it or lose it tissues, so if the dinosaurs didn’t use their arms in adulthood, the arms should be pretty weak in adults but very strong in juveniles. Thus we should see signs of atrophy in the fossils, and since we don’t, we assume that even if they may have served more purpose as an immature, they must still be used by the adults.
This is actually something scientists have discussed in connection with the controversy over Nanotyrannus, what was originally described as a genus of dwarf tyrannosaurs existing alongside t rex, but which now appears to be a juvenile t rex. The main reason it was treated as a distinct genus early on was it's disproportionately large arms for a t rex. But the counter argument is that the arms likely stopped developing after a certain point, and juvenile t rex using their arms to hunt but shifting to bite force dominated hunting as they age is the explanation given for why that happens.
Since reading the book “good enough”, I’ve realized not every trait is an adaptation selected for because of pressures. A lot of things happen in nature that just persist because they are good enough not to be eliminated. Nature is actually pretty forgiving, and a more accurate term than “natural selection” is “natural elimination”. Maybe the short arms came first and a purpose was made after. Or maybe in cohesion. Animals tend to do what they can with the limbs they have.
Even though T. Rex arms are proportionally shorter and smaller than their body size. A Tyrannosaurus Rex arms range inbetween 2-3ft long. Their arms were about the same length as our own human arms. And were much stronger than our adverage arms. Capable of lifting over 400 pounds with ease like a Male Chimpanzee.
I feed geese. I think they would use the hands to reposition their prey as they’re eating it. Maybe throw something on it’s back to avoid the rib cage? I also think they used the tail and didn’t get up “awkwardly” at all.
body part proportions change with age. In a newly hatched T. Rex, the forearms may have been proportionately larger, and served to help grasp and tear off smaller pieces of food. The arms would be closer to the mouth in the baby T. Rex. Maybe.
Yeah I could see that. Possibly helped them hunt and become the large beasts they were. And then once a gigantic predator no longer needing the forearm
@@michaelcorrigan6577 right. and when you look at the issue that the T. Rexes weren't just considered 'invasive species (it's closest kin, Tyrannosaurus or Tarbosaurus Bataar became dominant in Asia slightly earlier than T. Rex), but that as they established themselves in northern Laramidia, they also evolved to fill each niche of its new environment, you get to see what's going on. The babies were scuttling through the underbrush going after insects, lizards. The juveniles, working for the creatures that the big raptors didn't go for (or perhaps in competition with). The sub-adults were transitioning from speed to power, so were probably hunting the big duckbills. And finally, a fully grown Rex would be able to tackle the most dangerous prey, the armored ankylosaurids, the aggressive ceratopsians, and the giant alamosaurids of their area. So, when you add all that together, it's quite a formidable animal that could have used its arms in an entirely different manner as a rexling than the 'big brute' 16-18 years older that could not reach its chin.
I have often wondered if T-Rex's arms were truly vestigial, maybe even fully internal to the body like a whale's leg bones. Your explanation about nerve fibres and muscles helped me understand how scientists can tell they were actual arms.
@@aydensalerno8489 It was mentioned on 7 Days of Science, I think 2 weeks ago, on The Ben G. Thomas channel. They often have links to the studies in the descriptions.
@@aydensalerno8489 Ah, here it is. www.researchgate.net/publicat... And this is the link to the video where I saw it mentioned. ua-cam.com/video/N5_sRc6n6ts/v-deo.html
Most "walking" birds have the ability to run up trees to escape predators before flight feathers come in. Hoatzin climb around tree branches using wing claws. Perhaps young rexes used the arms in similar ways until they reached a size too big for most predators. Even bears and lions climb trees before they become too bulky.
@@deadmeme8973 Modern day birds do it and a week old chicken's wing can not support it's weight nor a chukars nor a pigeons. The birds are essentially "running" up the tree trunk, the wing hooks and beats just keep the body in the right posture. We do know rex arms were strong and all they'd need to do is keep the upper body close to a surface to prevent leaning back.
@@deadmeme8973Whoa calm down with the caps, its a hypothesis, not a statement of fact. Since neither of us were there, we probably will never know for sure. All modern day flighted and flightless birds do it, which suggests it's a foundation behavior. The legs of the animal does all the pushing up vertical surfaces, the wings in modern birds pull them towards the surface. In less steep inclines they simply run up it. In hoatzin and kakapo, the juvenile wing claws function like sloth claws meaning they have very little strength but do have incredible grip. It's not hard to imagine a juvenile rex running up and trunk, using it's arm clams in a failing motion to rapidly grip and release the trunk as it's legs propel it up. Once at a safe height those claws could be used to simply hold it in place while it's legs carry the weight. getting back down might prove a bit challenging. It's been studied as a ground up theory of flight evolution. It's a behavior that is universal to all birds. How do you know a hatchling or juvenile rex could not do the behavior? What is your theory?
Two ideas: One, they had feathers of some kind on their arms and the muscles were needed to perform mating displays. Two, they were needed to gather nesting material to cushion the fall of the egg from a cloaca 10 feet off the ground. The inward facing claws are like the hooks on the end of bungee straps holding vegetation to the chest as the animal returns to the chosen site.
Display structures. Yeah, I know, it's the go-to nowadays, so sue me. But imagine Rexy having a line of bright iridescent feathers on each arm. When he's trying to impress a mate, he holds out his arms, fans his feathers, and wiggles those two claws to make the fan shimmy around, peacock-style.
maybe that was one of its purposes, but the arms were far too bulky and strong to simply be for display. I say it was multifunctional as most things are.
@@francesconicoletti2547 Not necessarily. Look at a peacock - those giant feather tails of theirs are attached to a practically vestigial tail. It would make sense for Rex to have big muscles on vestigial arms if the muscles were being used to control large feathers.
I find it unlikely, these kind of display structures are most commonly found on smaller animals. It is a way to show strength and “ look I don’t fear those predators” to the females. It is pretty common on today’s birds probably because they occupy these ecological niches, these kind of behaviours are not really present in birds of prey. I don’t see why a large theropod would engage in such display demonstrations. Every single tyrannosaurus specimen have been found with signs of bite marks from others tyrannosaurus rexes, so it might be due to fights during the mating season.
Not impossible, but I think still unlikely. The arms look to be used for holding something down under it. And the arms look unsuited for violence. Only another T-rex will sit willingly under a T-tex. So a youngster don't need (much) larger frontlegs, as their purpose is probably for mating, and not for hunting.
Would be interesting to find out if there were feathers on the arms, as we know therapods did have them, that maybe made them appear larger and could be used for temperature regulation or displaying colours.
Damn. If I had been cornered by a T-Rex my strategy would have been to challenge him to an an arm wrestle and let me go if I win. Now it seems even that's not gonna work.
There’s an interesting correlation between the size of carnivorous dinosaurs arms and the size of their skulls. Generally the larger the skull the smaller the arms. I read a paper once that suggested that this is a general trend and that having massive jaws puts anything in front of those jaws in danger of being bitten off or becoming infected. So the evolutionarily advantageous response to favoring a bigger bite was to shrink one’s arms. I liked that hypothesis because it explains the evolutionary pressure which requires the arms to become vestigial. No need to claw something if you can just bite off 40 pounds of meat at once.
The similarity is due to function. Two bones are needed on the lower arm in order to twist the hand at the wrist... you know, to open door knobs ;) but you get what I mean.
There was one hypothesis u missed that I personally think is the most likely explanation for their relatively small arms. This theory suggests that tyrannosaurus used their arms more in their early stages of development. Going off record here. I personally like this theory since other mega theropods like giganotosaurus and acrocanthosaurus who are only distantly related had small arms relatively to their body size aswell.
I'm skeptical about the hypothesis that the arms were used for getting up. Their center of gravity was at their hips, so there should be no balancing issue, their legs were clearly much more powerful than their arms, not to mention that the arms would barely extent from their chest and belly, keeping in mind that they can't even extend 180 degrees.
I'd not so much imagine the arms being used to 'push' the animal up but serving more as anchor points as the legs do the work. As seen in a lot of large mammals when they rise from a resting position, they will raise their back legs first which rolls the centre of gravity forward and puts less strain on the bones of the back legs. Once erect, they tend to then push backwards with the front legs, rolling the centre of gravity back towards the rear legs as the front legs stand up. It's quite plausible that T-rex would would use this sort of 'rocking' motion during the process of standing as well (Emus will sometimes do this as well, briefly using their flat sternum as a grounding point as they position their legs for lifting). As the legs lift the rear of the animal though, the shift in weight would cause the body to want to slide forward. While friction between the chest and the ground might be enough to resist sliding, the position of the arms would make them useful in acting as anchor points until the tail and hips are up, which then, they could offer some push to get the centre of gravity back over the legs. In such a situation, the reduction of fingers to instead have just two, rigid claws would make sense. I'd not jump on it as 'proof', but I can definitely see it working (but not really for 'lifting' the animal directly).
@@grahamstrouse1165 A 200kg push is far better than nothing. And in combination with say, the t.rex. yanking its head back for lifting power (like some birds do) it might be helpful enough. They probably used it for many things though, not just one singular purpose.
Think of energy like points, if you don't invest many of those points in one area that gives you more points to spend in other areas. By having such small arms, large theropods can divert that energy towards getting that slightly bigger overall or developing their head just a little bit more. It only takes the slightest advantage to make something evolutionarily advantageous enough to be worth passing down.
There’s something still so exciting about T.Rex. Maybe because it’s so well studied compared to other dinosaurs but man I could watch an entire in depth series about Rexy.
Here’s another theory- once the T-Rex has a decent bite on a victim, they could have used the relatively small but still powerful limbs to slash at the prey (or rival) draw blood, disembowel, or disable limbs. We always see drawings of these limbs dangling from the upper torso, but there’s no reason they couldn’t have had enough range of motion to make effective in close weapons, slashing and grabbing at a variety of angles, without taking up too much of the attachments required for the neck muscles.
@6:20 but theyd then be good at defense for the underside...? Slashing claws close to the underside. May be why they weren't even smaller. And any longer and they'd only be slashing where the hind legs could get to easily. Maybe they were a stop-gap covering the only bit that the head and legs weren't defending.
These animals - T-Rex in particular - sacrificed virtually every part of their body to maximize bite force. I love it. No need to claw or otherwise grapple with prey when your bite is so lethal. The idea that these tiny arms were actually quite powerful is rather funny lol
I would be willing to bet that the primary purpose of the tiny small arms are for mating. The tail of the female is so thick and large, there’s really no way to mount the female T-Rex unless she put her head completely on the ground which would lift the tail into the air. Her strong tiny hands with the big claws would hold her in position on the ground without rolling over. At this point, her tail would almost be vertical which would allow the male to mount from behind. Next, the male T-Rex could then easily mount the female in his vertical position and used his strong hands and curved claws to hold onto the female tail by wrapping his hands around it. It’s actually a perfect fit system if you can get imagine what I’m talking about. It’s really the only way they can mate with such a thick tail. The small arms on the female keep her in position on the ground for the mount while the small arms on the male use them to lock the female tail. It’s actually pretty obvious if you think about it.
If you model the range of motion you'll deduce, correctly, that Trex needed to move its offspring from place to place. A vibrant world brimming with opportunistic creatures would easily have taken the opportunity to snack on newly hatched chicks. Given its size it would have needed to follow herd animals and avoid lost broods
We need to see the uncut, longer version of this video which featured a visual recreation of two T-Rexes fumbling around during mating, using their proportionally tiny arms, to better understand what you meant at 04:55. Also, in thinking a good way to try and understand how they used their arms might be through simulation. While we wait for more archaeological evidence, we could be using computing to model their bodies and behaviour and try machine learning to see how this "Si-Rex" uses its similarly proportionally tiny arms.
Thank you for a thought provoking and well illustrated video! This question is not informed but worth sharing. I’ll add my inquiry to others who have wondered whether short arms may have been more useful earlier in the maturation process. I wonder if the arms may have been relatively longer when young, and I wonder if they may have seemed more useful during that stage of the individual’s development?
The tiny arms were used during love-making. T.Rex most likely tickled its companion as part of its mating ritual. Essentially, it was the T.Rex equivalent of fingerblasting your mate. The reduction of the digits, while keeping the main two fingers of the hand, as we all know from experience, would only make them more effective and efficient at this task
I think it was Adrian Desmond’s book in the 1970’s that first mentioned the arms were retained to get off the ground after sleeping - to aid the Tyrannosaur in not scraping it’s head on the ground when getting up.
I'm no expert, but I daresay they probably were losing those limbs entirely, the same way the snake lost all four of its limbs. I think it's the python that still has some vestigial hind toes, which it uses to tickle its mate. Maybe that's how the Trex uses its fore-legs.
I know the PBS Eons video was made well after this one, but perhaps the arms played a much larger role in the early life of Tyrannosaur. The Eon's vid suggests that Tyrannosaurs occupied different niches at different times of their lives so it may be that they needed strong clawed hands when young to help catch prey and/or tear up and support themselves on carcasses. Then later in life they switched to using their jaws more and more the bigger they got until their arms were diminished in comparison by the time they reached full size. So all the theories are correct just at different times in a Tyrannosaur's life. This would also why other unrelated animals also had similar arms. Of course this doesn't explain why Carnotaurus didn't seem to have any use for it's arms at all either despite probably being in a similar situation and needing to hunt/scavenge different types of animals as it grew as well.
1:55 i think its more likely a "the arms just didnt grow as much as the rest" than "reducing the size of the arms" a not entirely trivial matter of perspective
Like Apple deciding to remove the headphone jack to make "more room" for not so new features, so too the space needed for the neck muscles on of the T-rex.
DRINKING GAME!!! Take a sip of your drink when there is: - a time lineage - a genetic tree - a new illustration - a size comparison Take a shot when: - the narrator says "however"
I am a fan of the idea the T-Rex was a slow lazy creature that would need to warm up in the sun like a lizard or superman. It would use its arms to grab on a preys bones like eagle claws into a fish. It's also fun to think of them acting like a magpie guarding a nest. You know, the whole false attack thing fly by.
Maybe they used their arms which had the increased pressured points from the two fingered claws more as a weapon while they were growing up. They might have had smaller frames and heads while young/adolescent and needed the claws more to hunt. Then, when they got bigger frames, bulkier bodies and gigantic heads they relied on the claws less for hunting and more for gripping while mating or pushing themselves off the ground, etc.
Yes, possible explanation is that the male held on to the female with these arms while mating (like birds). But that then does not explain why the female had small arms 🤣
I've always thought it was for mating. Typically things like this are multipurpose, they use them for whatever they possibly could. Carrying young, gripping the right prey, etc
What if the T-Rex was using those arms for nesting. To avoid crushing the eggs, T-Rex would have to sit behind the nest and would rely on his arms to do nesting stuff as his jaw woud be too overkilling on the task and dangerous for the eggs. I like to imagine that those arms would be covered with long fuzz to keep the eggs warm. And maybe those arms would also be useful for early life. When they are young, the arms have more normal proportions compared to the rest of the body. This could help to climb to trees to avoir predation.
I always thought the most likely use of those little forearms was nesting. While soft-shelled reptile eggs can be left buried in sand, hard-shelled bird eggs must be turned regularly to distribute albumin to the fetus. Birds do this (every few hours) with their beaks and/or feet, but the great heavy head and big hind feet of Tyrannosaurus Rex would have been poorly suited for this delicate job. I understand that T-Rex had hard-shelled eggs, which may have had the same need of being turned, and having small front feet for turning them might even have been the only way to manage this. Those small feet could also have been useful for scraping out the nest cavity in preparation for laying and for pulling out trash after hatching (broken shells, leftover or dropped food and, not least, baby poo). So I was surprised not to hear this guess here - has anyone considered this possibility? UPDATE: I used to raise canaries and just watched a video to remind myself how small birds manage. Small nesting birds use their feet and a rapid shuffling action with their bellies to move the eggs around. If T-Rex actually incubated her eggs, which is hard to imagine given the bulk involved, she'd need something equivalent to those little legs to get the same effect. It's possible that T-Rex had a nimble tongue for eating poo and old or dropped food. And they might have been pretty handy with their teeth: American alligators are amazingly dexterious with their toothy mouths in picking up babies and carrying them about. But they do this when the hatched babies are out of the nest; they lay soft-shelled eggs that they don't have to turn and they don't have to maintain the nest aside from guarding it. Given all this, I'd think the case for those little legs being needed by T-Rex for nesting is at least highly plausible.
Probably has the same function as some oddly-shaped shark heads: gripping & digging into large prey items to get the largest bites possible. With such a large jaw, T-Rex was probably spending a significant amount of energy just to move their head around and bite. Being able to break open carcasses would have been of great advantage as it would require less work for the T-Rex's jaw and would likely have aided in digestion.
+Moth Light Media You are missing the whole point of Carrier's constraint (the observation that air-breathing vertebrates which have two lungs and flex their bodies sideways during locomotion find it very difficult to move and breathe at the same time) T-Rex were reptiles, and they could have developed front legs the same way crocodiles or comodo dragons did, but they needed to breath while hunting and to do so with the anatomy that repiles have, they couldn't use their front legs
Interesting to also look at the terror birds, which had evolved a very similar body and head shape to T-Rex (only with a sharp beak and no teeth). They also had tiny little wings.
I think they could have been used in mating disputes. I picture the way elephant seals fight to try and dominate rather than kill. The idea that the animal grew out of their use through adolescence to adulthood is pretty interesting as well. Makes sense to me
Adding to the list of potential fore-limb use: -Signalling while pack hunting, silent gestures are very helpful in an ambush attack style. -Carrying large prey items away for later use. Transporting the own young. -Manipulating plants for camouflage, comfort, nesting...(tools ?) -Climbing/catching prey while very young. Behaviouristic evidence sadly does not fossilise well, so lets speculate here !
Nice video. But: Just because a similar jet unrelated animal showed a comparable reduction in the arms doesn't imply a function of the arms. It could rather show, that two finger can be the default way to form back a limb. I’m not up to date, but as far as I know, we find a pattern within the tyrannosaurids that the attachment area for ligaments is shrinking, the curvature of the claws is reduced and the relative size of muscle attachment within the arm is also getting smaller. All this points into the direction of a remnant limb that going to become vestigial like in carnotaurus.
Maybe T-Rex held intense Banjo jam sessions after hunts, that's why the muscles were scarred. Heck they might have done daily pushup sets to avoid being ridiculed for the tiny limbs.
I've got my own hypothesis, but I fear sharing it as its a keystone to what I'd eventually want to use for a Doctoral Thesis... ...Also it sounds and probably LOOKED rather ridiculous, but helps in the speed vs stability argument of T. rexes biomechanics.
it really puts things in perspective that, while T rex has tiny arms, its arms are still longer than our own arms.
While being three to four times stronger, meaning they had to have done SOMETHING!
Those arms really are deadly for humans, one slash from them would wipe you out!
that makes them seem even sillier. i thought they were bigger than that. 3-4 times stronger than a human arm is negligible for an animal that large
@@DevinDTV Well you have to understand that most of the muscle in the shoulder area of a T. rex is dedicated to the neck and jaw.
Many large carnivorous Theropods developed along these lines, to the point that Carnotaurus only has little nublets for arms that are way more vestigial looking that T. rexes.
They're joke arms on a beast as large as that, lol!👍🛸🍺🍻😷😁👍
Was the arm more balanced when the T-Rex was younger? Every dinosaur had to start from the size of an egg, and maybe it played a role in the child/adolescent stage of the T-Rex's life?
Where in nature is this seen?
@@christopherellis2663
Differing proportions over life stages is extremely common in nature.
humans for one, we have proportionally larger heads as infants than as adults, we also grow additional molars as we mature.
In almost all insects major morphological changes occur from egg to adult. Most extreme being the endopterygota which undergo complete metamorphosis.
If we’re talking about the concept of maintaining juvenile features into adulthood, the phenomenon, called neoteny is pretty widespread. The axolotl being a prime example.
In terms of maintaining structures which only serve a function in immature organisms there are examples of this as well, the belly button is a good one.
@@christopherellis2663 lots of different places within the animal kingdom, juveniles having a different lifestyle and by extension different anatomy is fairly common among animals.
The problem with this idea is that there is muscle scarring on adult T-Rex skeletons.
Muscles are kind of use it or lose it tissues, so if the dinosaurs didn’t use their arms in adulthood, the arms should be pretty weak in adults but very strong in juveniles. Thus we should see signs of atrophy in the fossils, and since we don’t, we assume that even if they may have served more purpose as an immature, they must still be used by the adults.
This is actually something scientists have discussed in connection with the controversy over Nanotyrannus, what was originally described as a genus of dwarf tyrannosaurs existing alongside t rex, but which now appears to be a juvenile t rex. The main reason it was treated as a distinct genus early on was it's disproportionately large arms for a t rex. But the counter argument is that the arms likely stopped developing after a certain point, and juvenile t rex using their arms to hunt but shifting to bite force dominated hunting as they age is the explanation given for why that happens.
Since reading the book “good enough”, I’ve realized not every trait is an adaptation selected for because of pressures. A lot of things happen in nature that just persist because they are good enough not to be eliminated. Nature is actually pretty forgiving, and a more accurate term than “natural selection” is “natural elimination”. Maybe the short arms came first and a purpose was made after. Or maybe in cohesion. Animals tend to do what they can with the limbs they have.
"Good Enough : The Tolerance for Mediocrity in Nature and Society" is this the Book?
@@alexcontreras6103 yessir
@@Grand_History Ok sweet I got it looks interesting
@@alexcontreras6103 It’s great. It kind of makes you realize modern biologists don’t often approach science the correct way
@@Grand_History Interesting that gets me hyped. Love reading things that put things in a different perspective
“These tiny arms could be terrifying weapons” is a really funny sentence
That's what I say to people who want to fight me
He says, "these FUNNY arms"
@@jamesbentonticer4706 so sorry for this massive spelling mistake. Please forgive me.
Even though T. Rex arms are proportionally shorter and smaller than their body size. A Tyrannosaurus Rex arms range inbetween 2-3ft long. Their arms were about the same length as our own human arms. And were much stronger than our adverage arms. Capable of lifting over 400 pounds with ease like a Male Chimpanzee.
The arms were only tiny in comparison to a fully grown trex. They were the size of a grown man’s so very strong
"*stumped* scientists for years" - lol
Oooooo
I feed geese. I think they would use the hands to reposition their prey as they’re eating it. Maybe throw something on it’s back to avoid the rib cage?
I also think they used the tail and didn’t get up “awkwardly” at all.
They don’t have stumps. They have tiny arms stop crowbaring crap jokes in any way you can
lolololol the cringe is strong
BA-DUM-TSSSSSSS
🥁🥁🥁
body part proportions change with age. In a newly hatched T. Rex, the forearms may have been proportionately larger, and served to help grasp and tear off smaller pieces of food. The arms would be closer to the mouth in the baby T. Rex. Maybe.
Well Nanotyrannus, which scientist now support as Juvenile T-rex have proportionally larger arm and likely being used.
Yeah I could see that. Possibly helped them hunt and become the large beasts they were. And then once a gigantic predator no longer needing the forearm
@@michaelcorrigan6577 right. and when you look at the issue that the T. Rexes weren't just considered 'invasive species (it's closest kin, Tyrannosaurus or Tarbosaurus Bataar became dominant in Asia slightly earlier than T. Rex), but that as they established themselves in northern Laramidia, they also evolved to fill each niche of its new environment, you get to see what's going on. The babies were scuttling through the underbrush going after insects, lizards. The juveniles, working for the creatures that the big raptors didn't go for (or perhaps in competition with). The sub-adults were transitioning from speed to power, so were probably hunting the big duckbills. And finally, a fully grown Rex would be able to tackle the most dangerous prey, the armored ankylosaurids, the aggressive ceratopsians, and the giant alamosaurids of their area. So, when you add all that together, it's quite a formidable animal that could have used its arms in an entirely different manner as a rexling than the 'big brute' 16-18 years older that could not reach its chin.
@@Neon_White Nutz.
why need arms when you have that much swag
Swagosaurus Rex
I've always wondered why dinosaurs had tiny arms and also why do women have ears?
What's this? My favorite Paleontology UA-camr is back?
Wonderous upon wonder!
I have often wondered if T-Rex's arms were truly vestigial, maybe even fully internal to the body like a whale's leg bones. Your explanation about nerve fibres and muscles helped me understand how scientists can tell they were actual arms.
There was a recent imprint discovered of a Tyrannosaurs having pushed itself up using its forelimbs after squatting to eat.
That sounds awesome, can you give the source.
@@aydensalerno8489 It was mentioned on 7 Days of Science, I think 2 weeks ago, on The Ben G. Thomas channel. They often have links to the studies in the descriptions.
@@aydensalerno8489 Ah, here it is. www.researchgate.net/publicat...
And this is the link to the video where I saw it mentioned. ua-cam.com/video/N5_sRc6n6ts/v-deo.html
@@WaterShowsProd Great, thanks.
@@WaterShowsProd 'page not found' :(
I wonder if it could have helped them turn their eggs or arrange their nest. I can’t imagine how else they could manage something so delicate.
Crocodiles do it with their mouth
Most "walking" birds have the ability to run up trees to escape predators before flight feathers come in. Hoatzin climb around tree branches using wing claws. Perhaps young rexes used the arms in similar ways until they reached a size too big for most predators. Even bears and lions climb trees before they become too bulky.
Same with the Komodo dragons.
very possible
@@deadmeme8973 Modern day birds do it and a week old chicken's wing can not support it's weight nor a chukars nor a pigeons. The birds are essentially "running" up the tree trunk, the wing hooks and beats just keep the body in the right posture. We do know rex arms were strong and all they'd need to do is keep the upper body close to a surface to prevent leaning back.
@@deadmeme8973 plenty of youtube vids on juvenile birds running up tree trunks to see what i'm getting at.
@@deadmeme8973Whoa calm down with the caps, its a hypothesis, not a statement of fact. Since neither of us were there, we probably will never know for sure. All modern day flighted and flightless birds do it, which suggests it's a foundation behavior. The legs of the animal does all the pushing up vertical surfaces, the wings in modern birds pull them towards the surface. In less steep inclines they simply run up it. In hoatzin and kakapo, the juvenile wing claws function like sloth claws meaning they have very little strength but do have incredible grip. It's not hard to imagine a juvenile rex running up and trunk, using it's arm clams in a failing motion to rapidly grip and release the trunk as it's legs propel it up. Once at a safe height those claws could be used to simply hold it in place while it's legs carry the weight. getting back down might prove a bit challenging. It's been studied as a ground up theory of flight evolution. It's a behavior that is universal to all birds. How do you know a hatchling or juvenile rex could not do the behavior? What is your theory?
Two ideas: One, they had feathers of some kind on their arms and the muscles were needed to perform mating displays. Two, they were needed to gather nesting material to cushion the fall of the egg from a cloaca 10 feet off the ground. The inward facing claws are like the hooks on the end of bungee straps holding vegetation to the chest as the animal returns to the chosen site.
I like the nest idea, but you know birds don’t lay eggs standing straight up right? They squat down with the vent on the ground.
Display structures. Yeah, I know, it's the go-to nowadays, so sue me. But imagine Rexy having a line of bright iridescent feathers on each arm. When he's trying to impress a mate, he holds out his arms, fans his feathers, and wiggles those two claws to make the fan shimmy around, peacock-style.
Used them kinda like those guys with torches directing planes?
But then the arms should be skinny & long with lots of claws for maximum display space not strong & short with few claws.
maybe that was one of its purposes, but the arms were far too bulky and strong to simply be for display. I say it was multifunctional as most things are.
@@francesconicoletti2547 Not necessarily. Look at a peacock - those giant feather tails of theirs are attached to a practically vestigial tail. It would make sense for Rex to have big muscles on vestigial arms if the muscles were being used to control large feathers.
I find it unlikely, these kind of display structures are most commonly found on smaller animals. It is a way to show strength and “ look I don’t fear those predators” to the females. It is pretty common on today’s birds probably because they occupy these ecological niches, these kind of behaviours are not really present in birds of prey.
I don’t see why a large theropod would engage in such display demonstrations. Every single tyrannosaurus specimen have been found with signs of bite marks from others tyrannosaurus rexes, so it might be due to fights during the mating season.
Something about your videos is so relaxing, I can't help but fall asleep even though it genuinely interests me
Has anyone considered that the arms may have been in larger use during the animals younger growth stages?
Ok
Like Hoatzins?
Ditto. My thoughts exactly.
Not impossible, but I think still unlikely. The arms look to be used for holding something down under it. And the arms look unsuited for violence. Only another T-rex will sit willingly under a T-tex. So a youngster don't need (much) larger frontlegs, as their purpose is probably for mating, and not for hunting.
Would be interesting to find out if there were feathers on the arms, as we know therapods did have them, that maybe made them appear larger and could be used for temperature regulation or displaying colours.
Your onto something there.
Damn. If I had been cornered by a T-Rex my strategy would have been to challenge him to an an arm wrestle and let me go if I win.
Now it seems even that's not gonna work.
Somewhere out there a little fossilized piano waits to be found
There’s an interesting correlation between the size of carnivorous dinosaurs arms and the size of their skulls. Generally the larger the skull the smaller the arms. I read a paper once that suggested that this is a general trend and that having massive jaws puts anything in front of those jaws in danger of being bitten off or becoming infected. So the evolutionarily advantageous response to favoring a bigger bite was to shrink one’s arms. I liked that hypothesis because it explains the evolutionary pressure which requires the arms to become vestigial. No need to claw something if you can just bite off 40 pounds of meat at once.
It would be interesting to discuss where Dinosaur evolution was heading before the Yucatan ELE? Could you do a video?
Dinosaurs still exist. We call them birds now.
@@oldcountryman2795 dont be a smartass, he's obviously talking about theropod dinosaurs
@@chaseblackstone8749 Birds are theropod dinosaurs
@@acrocanthos-maxima4504 He was clearly talking about your mom tho
@@Tracker947 Oh thanks, my bad
5:55 should also mention that some species of oviraptorids evolved to have 2 digits
3:42 I like to think that this dinosaur is just called “Fred”.
Btw, I just found this channel and it’s sooo goood! Thank you!
It’s crazy to me how the bones in the Trexs arms are so similar to the bones we have today
The similarity is due to function. Two bones are needed on the lower arm in order to twist the hand at the wrist... you know, to open door knobs ;) but you get what I mean.
All vertebrate life is build up from the same system. Vertebrates are one family
There was one hypothesis u missed that I personally think is the most likely explanation for their relatively small arms.
This theory suggests that tyrannosaurus used their arms more in their early stages of development.
Going off record here. I personally like this theory since other mega theropods like giganotosaurus and acrocanthosaurus who are only distantly related had small arms relatively to their body size aswell.
I'm skeptical about the hypothesis that the arms were used for getting up. Their center of gravity was at their hips, so there should be no balancing issue, their legs were clearly much more powerful than their arms, not to mention that the arms would barely extent from their chest and belly, keeping in mind that they can't even extend 180 degrees.
I'd not so much imagine the arms being used to 'push' the animal up but serving more as anchor points as the legs do the work. As seen in a lot of large mammals when they rise from a resting position, they will raise their back legs first which rolls the centre of gravity forward and puts less strain on the bones of the back legs. Once erect, they tend to then push backwards with the front legs, rolling the centre of gravity back towards the rear legs as the front legs stand up. It's quite plausible that T-rex would would use this sort of 'rocking' motion during the process of standing as well (Emus will sometimes do this as well, briefly using their flat sternum as a grounding point as they position their legs for lifting). As the legs lift the rear of the animal though, the shift in weight would cause the body to want to slide forward. While friction between the chest and the ground might be enough to resist sliding, the position of the arms would make them useful in acting as anchor points until the tail and hips are up, which then, they could offer some push to get the centre of gravity back over the legs. In such a situation, the reduction of fingers to instead have just two, rigid claws would make sense. I'd not jump on it as 'proof', but I can definitely see it working (but not really for 'lifting' the animal directly).
@@demetrialowther727 Not with the kind of mass they’d be pushing against.
@@grahamstrouse1165 A 200kg push is far better than nothing. And in combination with say, the t.rex. yanking its head back for lifting power (like some birds do) it might be helpful enough. They probably used it for many things though, not just one singular purpose.
“I got a big head with little arms.” Legendary quote from T-Rex in Meet The Robinson
Think of energy like points, if you don't invest many of those points in one area that gives you more points to spend in other areas. By having such small arms, large theropods can divert that energy towards getting that slightly bigger overall or developing their head just a little bit more. It only takes the slightest advantage to make something evolutionarily advantageous enough to be worth passing down.
There’s something still so exciting about T.Rex. Maybe because it’s so well studied compared to other dinosaurs but man I could watch an entire in depth series about Rexy.
Here's my idea: they used their arms for komodo dragon style territorial wrestling.
I mean, that's conjecture, but it's a neat idea.
Honestly that and getting up off the ground sound like good ones, although egg manipulation might be another one
@@kumiq17 That's such a cute image. Until directly told it's inaccurate that's what I'll be imagining.
I love how you use the most accurate renditions of Tyrannosaurus.
Here’s another theory- once the T-Rex has a decent bite on a victim, they could have used the relatively small but still powerful limbs to slash at the prey (or rival) draw blood, disembowel, or disable limbs.
We always see drawings of these limbs dangling from the upper torso, but there’s no reason they couldn’t have had enough range of motion to make effective in close weapons, slashing and grabbing at a variety of angles, without taking up too much of the attachments required for the neck muscles.
the slight moving background is so appealing
Maybe they had colourful feathers attached and were used for display. Or some other intraspecies interaction.
Glad I found this channel keep up the good work man!
Very informative - thanks. Those are some nice illustrations as well - kudos to the artists.
@6:20 but theyd then be good at defense for the underside...? Slashing claws close to the underside. May be why they weren't even smaller. And any longer and they'd only be slashing where the hind legs could get to easily. Maybe they were a stop-gap covering the only bit that the head and legs weren't defending.
I'd love to see machine learning be put towards understanding the arm function. Great vid.
Moth Light Media and Eons are my favorite paleo channels
These animals - T-Rex in particular - sacrificed virtually every part of their body to maximize bite force. I love it. No need to claw or otherwise grapple with prey when your bite is so lethal.
The idea that these tiny arms were actually quite powerful is rather funny lol
I love this channel so much.
I would be willing to bet that the primary purpose of the tiny small arms are for mating. The tail of the female is so thick and large, there’s really no way to mount the female T-Rex unless she put her head completely on the ground which would lift the tail into the air. Her strong tiny hands with the big claws would hold her in position on the ground without rolling over. At this point, her tail would almost be vertical which would allow the male to mount from behind.
Next, the male T-Rex could then easily mount the female in his vertical position and used his strong hands and curved claws to hold onto the female tail by wrapping his hands around it. It’s actually a perfect fit system if you can get imagine what I’m talking about. It’s really the only way they can mate with such a thick tail. The small arms on the female keep her in position on the ground for the mount while the small arms on the male use them to lock the female tail. It’s actually pretty obvious if you think about it.
If you model the range of motion you'll deduce, correctly, that Trex needed to move its offspring from place to place. A vibrant world brimming with opportunistic creatures would easily have taken the opportunity to snack on newly hatched chicks. Given its size it would have needed to follow herd animals and avoid lost broods
Big overlap to answers to questions like "Why do flightless birds have such useless wings?" or "Why do whales have such rudimentary pelvises?"
We need to see the uncut, longer version of this video which featured a visual recreation of two T-Rexes fumbling around during mating, using their proportionally tiny arms, to better understand what you meant at 04:55.
Also, in thinking a good way to try and understand how they used their arms might be through simulation. While we wait for more archaeological evidence, we could be using computing to model their bodies and behaviour and try machine learning to see how this "Si-Rex" uses its similarly proportionally tiny arms.
Thank you for a thought provoking and well illustrated video! This question is not informed but worth sharing. I’ll add my inquiry to others who have wondered whether short arms may have been more useful earlier in the maturation process. I wonder if the arms may have been relatively longer when young, and I wonder if they may have seemed more useful during that stage of the individual’s development?
Imagine t-rex with long beefy clawed arms, evolution missed out on making it even more horrifying
They’ve “stumped” scientists..
I see what you did there.
Welcome back
The T Rex was already a menace imagine if it had bigger arms. Absolute unit.
The tiny arms were used during love-making. T.Rex most likely tickled its companion as part of its mating ritual. Essentially, it was the T.Rex equivalent of fingerblasting your mate. The reduction of the digits, while keeping the main two fingers of the hand, as we all know from experience, would only make them more effective and efficient at this task
(blush)
Wow I really love your channel.
1:30 I thought that said Egoraptor at first, I was like, "Hey, it's Arin!"
I enjoyed your video thank you
Great vid! Please do the evolution of mustelids like honeys badgers and wolverines.
super interesting as usual
The arms were used to immobilized prey by making them laugh uncontrollably
I think it was Adrian Desmond’s book in the 1970’s that first mentioned the arms were retained to get off the ground after sleeping - to aid the Tyrannosaur in not scraping it’s head on the ground when getting up.
Jeff Foxworthy said that T-Rex were so mean because their arms were too short to reach their Weiners.
I used to call an ex-boss a T-Rex. Not because he was a terror, but because his arms were too short to reach his wallet
I'm no expert, but I daresay they probably were losing those limbs entirely, the same way the snake lost all four of its limbs.
I think it's the python that still has some vestigial hind toes, which it uses to tickle its mate. Maybe that's how the Trex uses its fore-legs.
Absolutely love your videos! Interesting and easy to understand. Keep it up!
I know the PBS Eons video was made well after this one, but perhaps the arms played a much larger role in the early life of Tyrannosaur. The Eon's vid suggests that Tyrannosaurs occupied different niches at different times of their lives so it may be that they needed strong clawed hands when young to help catch prey and/or tear up and support themselves on carcasses. Then later in life they switched to using their jaws more and more the bigger they got until their arms were diminished in comparison by the time they reached full size. So all the theories are correct just at different times in a Tyrannosaur's life. This would also why other unrelated animals also had similar arms.
Of course this doesn't explain why Carnotaurus didn't seem to have any use for it's arms at all either despite probably being in a similar situation and needing to hunt/scavenge different types of animals as it grew as well.
Love the video, but just an FYI: whenever the art at 0:12 comes on the screen, the artist is Jacob Baardse, not RJ Palmer
1:55 i think its more likely a "the arms just didnt grow as much as the rest" than "reducing the size of the arms" a not entirely trivial matter of perspective
Or maybe they needed small arms to manipulate social media on their mobile phones!
LOL! HA! HA! HA!
Very good! I liked this segment. Now you just need to do one about australian dinosaurs.
Like Apple deciding to remove the headphone jack to make "more room" for not so new features, so too the space needed for the neck muscles on of the T-rex.
T-Rex V2 Pro: Head sold separately
DRINKING GAME!!!
Take a sip of your drink when there is:
- a time lineage
- a genetic tree
- a new illustration
- a size comparison
Take a shot when:
- the narrator says "however"
Kinda lame on a 7 minute video.
@@peekafch then watch two of them 💁♀️
Wow! Now I know why my history book says T. Rex didn't excel in arm wrestling contests.
You are like a second PBS Eons channel
I am a fan of the idea the T-Rex was a slow lazy creature that would need to warm up in the sun like a lizard or superman. It would use its arms to grab on a preys bones like eagle claws into a fish. It's also fun to think of them acting like a magpie guarding a nest. You know, the whole false attack thing fly by.
Because they would look wierd and creepy with long arms.
They would look cool with front legs.
Great as always
They were too short for picking their nose or scratching their bum. It must have been quite frustrating.
Perhaps they broke branches off trees to use as butt/nutscratchers
Maybe they used their arms which had the increased pressured points from the two fingered claws more as a weapon while they were growing up. They might have had smaller frames and heads while young/adolescent and needed the claws more to hunt. Then, when they got bigger frames, bulkier bodies and gigantic heads they relied on the claws less for hunting and more for gripping while mating or pushing themselves off the ground, etc.
I believe I read a while back that T-Rex may have used their small hands in mating as well cuz they could hold up to 500 lb
Yes, possible explanation is that the male held on to the female with these arms while mating (like birds). But that then does not explain why the female had small arms 🤣
I've always thought it was for mating. Typically things like this are multipurpose, they use them for whatever they possibly could. Carrying young, gripping the right prey, etc
Very good and new information here.
I can imagine that they might dig holes and Carry their eggs with it. Parenting like crocs do maybe.
What if the T-Rex was using those arms for nesting. To avoid crushing the eggs, T-Rex would have to sit behind the nest and would rely on his arms to do nesting stuff as his jaw woud be too overkilling on the task and dangerous for the eggs. I like to imagine that those arms would be covered with long fuzz to keep the eggs warm.
And maybe those arms would also be useful for early life. When they are young, the arms have more normal proportions compared to the rest of the body. This could help to climb to trees to avoir predation.
I always thought the most likely use of those little forearms was nesting. While soft-shelled reptile eggs can be left buried in sand, hard-shelled bird eggs must be turned regularly to distribute albumin to the fetus. Birds do this (every few hours) with their beaks and/or feet, but the great heavy head and big hind feet of Tyrannosaurus Rex would have been poorly suited for this delicate job. I understand that T-Rex had hard-shelled eggs, which may have had the same need of being turned, and having small front feet for turning them might even have been the only way to manage this. Those small feet could also have been useful for scraping out the nest cavity in preparation for laying and for pulling out trash after hatching (broken shells, leftover or dropped food and, not least, baby poo). So I was surprised not to hear this guess here - has anyone considered this possibility?
UPDATE: I used to raise canaries and just watched a video to remind myself how small birds manage. Small nesting birds use their feet and a rapid shuffling action with their bellies to move the eggs around. If T-Rex actually incubated her eggs, which is hard to imagine given the bulk involved, she'd need something equivalent to those little legs to get the same effect. It's possible that T-Rex had a nimble tongue for eating poo and old or dropped food. And they might have been pretty handy with their teeth: American alligators are amazingly dexterious with their toothy mouths in picking up babies and carrying them about. But they do this when the hatched babies are out of the nest; they lay soft-shelled eggs that they don't have to turn and they don't have to maintain the nest aside from guarding it. Given all this, I'd think the case for those little legs being needed by T-Rex for nesting is at least highly plausible.
That sounds better than most ideas I've heard.
Great video
Probably has the same function as some oddly-shaped shark heads: gripping & digging into large prey items to get the largest bites possible. With such a large jaw, T-Rex was probably spending a significant amount of energy just to move their head around and bite. Being able to break open carcasses would have been of great advantage as it would require less work for the T-Rex's jaw and would likely have aided in digestion.
I could see a T-Rex using it's tiny arms to help it get off the ground and
for holding on while mating. but it was very interesting!!
Another really interesting video :)
Idk why but it’s funny that something so large and terrifying lays eggs.
I swear you always upload the same
day that PBS eons does
I always wondered if it had arms only because it was more important for them* to hatch but after youth pretty much were vestigial.
Edit: a word
+Moth Light Media
You are missing the whole point of Carrier's constraint (the observation that air-breathing vertebrates which have two lungs and flex their bodies sideways during locomotion find it very difficult to move and breathe at the same time) T-Rex were reptiles, and they could have developed front legs the same way crocodiles or comodo dragons did, but they needed to breath while hunting and to do so with the anatomy that repiles have, they couldn't use their front legs
Interesting to also look at the terror birds, which had evolved a very similar body and head shape to T-Rex (only with a sharp beak and no teeth). They also had tiny little wings.
The arms are useful for juvenile. But it won't grow for adults.
I think they could have been used in mating disputes. I picture the way elephant seals fight to try and dominate rather than kill.
The idea that the animal grew out of their use through adolescence to adulthood is pretty interesting as well. Makes sense to me
What if t rex used their arms more when they were younger when the arms size was closer to their body size.
Tiny arms = dinosaur version of murder weapon
Adding to the list of potential fore-limb use:
-Signalling while pack hunting, silent gestures are very helpful in an ambush attack style.
-Carrying large prey items away for later use. Transporting the own young.
-Manipulating plants for camouflage, comfort, nesting...(tools ?)
-Climbing/catching prey while very young.
Behaviouristic evidence sadly does not fossilise well, so lets speculate here !
It's amazing, when you think about it, these creatures are basically just mouths with legs lol
It's crazy to imagine a giant walking lizard with no arms.....just legs and a mouth lol
Nice video. But: Just because a similar jet unrelated animal showed a comparable reduction in the arms doesn't imply a function of the arms. It could rather show, that two finger can be the default way to form back a limb. I’m not up to date, but as far as I know, we find a pattern within the tyrannosaurids that the attachment area for ligaments is shrinking, the curvature of the claws is reduced and the relative size of muscle attachment within the arm is also getting smaller.
All this points into the direction of a remnant limb that going to become vestigial like in carnotaurus.
Maybe T-Rex held intense Banjo jam sessions after hunts, that's why the muscles were scarred. Heck they might have done daily pushup sets to avoid being ridiculed for the tiny limbs.
I've got my own hypothesis, but I fear sharing it as its a keystone to what I'd eventually want to use for a Doctoral Thesis...
...Also it sounds and probably LOOKED rather ridiculous, but helps in the speed vs stability argument of T. rexes biomechanics.