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In the near future we have the technology to clone prehistoric animals. Although it will not be the same as the original, certainly we can make a meaner version of it.

Especially when it comes to Tyrannosaurus rex which had a very tiny arms relative to its body size, this comes as a surprise for many people especially the stakeholders financing the cloning project anonymously.

Is there a good reason not designing this once an apex predator of its time to have a bigger and stronger arm that can actually do serious damage to building structures and vehicles?

Since the clone is already almost 1.5 times as big as the original, why might we not as well also blow up the size of the arms to 2 or even 3 times bigger?

The scientist had calculated the maximum size for T-Rex by factoring in both the square cube law and nervous impulse. That limit would be around 10x, but since this bioweapon is designed for speed, so 1.5x to 2x the size of its original just hits the mark perfectly.

I think bigger arms help the dinosaur to recover quickly from a lying position.

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    $\begingroup$ What lying position? T-rex don't lie down, they sit down like most birds. $\endgroup$
    – John
    Dec 10, 2021 at 10:29
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    $\begingroup$ I read somewhere that the small arms weren't weak. They were designed to lift the multi-ton creature in case it somehow found itself lying on the ground. The small movement was enough to get it standing again in combination with its hindlegs. I dont know if you can easily add more arm mass so far upfront of the creature without unbalancing it. Perhaps a longer tail to make up for it? $\endgroup$
    – Demigan
    Dec 10, 2021 at 11:42
  • $\begingroup$ Why bother with the drawing board when you could just clone Deinocheirus for that job instead? Right tool for the right job and all that. They'll both need respirators because we don't have enough oxygen in the atmosphere for them to live... if you're going to make genetic modifications, this seems a more logical place to start. $\endgroup$
    – J...
    Dec 10, 2021 at 21:42
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    $\begingroup$ So, an Indominus Rex from Jurassic World? $\endgroup$ Dec 11, 2021 at 4:51
  • $\begingroup$ Why not Therizinosaurus while at that... $\endgroup$ Dec 11, 2021 at 16:01

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Because it's complicated

Simply scaling up an animal is easy. Especially when the animal in question didn't stop growing in the first place, but only slowed down a bit. You just have to jack up the growth hormone production.

Significantly increasing the size of a limb? That's a much more complicated feat of genetic engineering, with a lot of its own problems. You're very likely to "break" other parts of the whole system as a side effect.

Because the Arm-Rex wouldn't know what to do

Dinosaurs were not the smartest of animals. Especially the big ones; you don't need to be smart if you're strong to survive.
So chances are the Rex wouldn't even know what to do with the bigger arms. Most likely, the changed body balance would just make it fall over all the time.

Because you don't need to

Have you looked at the teeth? have you looked at the legs? have you looked that this massive, long tail?
Adding bigger arms would most likely not add any more "danger potential"

As for the stakeholders...

If they're really surprised that a cloned version of an animal that's commonly known for having tiny arms has... tiny arms, I doubt they're actually intelligent enough to gather enough money to invest in such a costly enterprise.

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    $\begingroup$ +1, but you would be surprised at how dim-witted some very wealthy people can be, and what they will throw their money at. Being rich and able to invest in things like military dinosaurs doesn't mean you're smart. $\endgroup$
    – Seth R
    Dec 10, 2021 at 18:53
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    $\begingroup$ @SethR i'm not surprised. but isn't the point of worldbuilding SE to not be too tightly bound to the real world? ;) $\endgroup$ Dec 10, 2021 at 19:28
  • $\begingroup$ The T-Rex was likely social and as smart as some of our apes. It would likely be able to learn how to use its arms (hell, babies learn it when their brain size small by simple repetition. Its during the process of discovering their body). It would mean they would be able to learn some operations and tool use alongside their arms (besides that if you do build bio-engineered T-Rexes for military use a few brain adaptations would be high on the list). $\endgroup$
    – Demigan
    Dec 10, 2021 at 19:48
  • $\begingroup$ @Demigan Where did you get that T-Rex was as smart and social as some apes? I'm no expert in any way but I thought there are assumed to have been pretty dumb as far as large predators go. And comparing to a human baby is not a good idea, they are one of the best and fastest learners known to exist in nature. The amount of things a human learns between say 1 and 2 years old is bigger that what any other animal learns in their entire live time. $\endgroup$
    – quarague
    Dec 11, 2021 at 6:48
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    $\begingroup$ @Demigan Intelligence is a murky thing to measure, but it’s clear that the ratio of brain mass to body mass matters a lot more than brain mass alone. That’s why whales aren’t as smart as us despite having way heavier brains. And studies have found that, comparing dinosaur skulls to those of modern birds, T Rex was much closer to a pigeon or emu than a crow or parrot in terms of relative brain size. No way to know how they acted for certain of course, but the brain size metric you’re pointing to actually suggests that T Rex was pretty dumb. $\endgroup$ Dec 11, 2021 at 17:20
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Because small arms are NOT a weakness

Tyrannosaurus Rex evolved over millions of years to be as effective at surviving in its environment as it could be. One glance at a T-rex mouth and we know that, for them, "surviving" involved killing and eating lots of other animals.

So they must have been pretty close to some kind of local optimum and therefore fairly well optimised for running around killing stuff.

So the only edits we want to make are things that are good now, but were not then. When you gene-edit some extra size that makes sense, in nature the extra killyness provided by more size is weighed against the cost of needing more food. But, our warmachine T-Rex (M-Rex) will be fed by its handlers, so the "right size" in the wild (its default size) is not the same as the "right size" for battle. Giving M-rex a different mindset that is more easily tamed than the T-Rex also makes sense.

But arms are different. Proper arms were clearly detrimental to the wild T-rex (otherwise it would have had them), and if they were bad in the wild they are probably just as bad in combat.

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    $\begingroup$ It's worth noting that there's some speculation out there that "surviving" involved killing and eating lots of fruit, since while the T-Rex's mouth looks impressive the teeth were poorly anchored and it wasn't able to replace them like sharks can. $\endgroup$ Dec 10, 2021 at 17:07
  • $\begingroup$ Larger arms would probably cause balance issues. You'd have to increase the tail weight. That will slow down acceleration. And put more strain on the legs. You'll need stronger legs too. $\endgroup$
    – Arluin
    Dec 10, 2021 at 22:19
  • $\begingroup$ T. rex's big tail was its key to speed and hunting prowess sciencedaily.com/releases/2010/11/101115131127.htm - The spinosaurus is twice as heavy, with half as much bite force, at 21mph instead of 25mph. If you want '2 large arms both weaponised' - that's your man. But if you want, "optimized for running around killing stuff" +1, you need the 'biggest muscles in the tail attached to upper leg bones'... and no arms. $\endgroup$
    – Mazura
    Dec 11, 2021 at 9:11
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Military tactics often require mobility

You can't do much if you're too weighed down or off-balance. Giving the t-rex body plan bigger arms will simply be a detriment to it. It'll be too front-heavy, tipping over most of the time due to the large head already adding quite a lot of weight to the front of it and the tail being designed as both a counter-weight and mobility enhancer. The extra weight of arms will require a heavier/larger tail to restore balance, and the extra weight of both the arms and the larger tail will significantly increase the amount of mass the rex needs to move, requiring larger/stronger legs which will, again, increase its mass and require more muscles to keep up. Bigger rexes limit where they can be deployed at any particular moment, further limiting their usefulness when they'd only realistically be able to be deployed where tanks would easily take them out. Not only that, all of this extra stuff will require more sustenance to fuel, which might not be a problem for a military animal since it'll be fed but it certainly puts a hamper on the longevity of the animal's time in action. It's sort of like how rockets face problems, more fuel = more mass, more mass = requiring larger/stronger thrusters, larger/stronger rockets = more mass again, requiring more fuel to get the thing to where it needs to be. Simply put, less weight is always better.

If you really want to give it larger arms you'll have to move away from the t-rex body plan and go more toward a crocodilian quadrupedal plan. Such a design at the size of a t-rex would make more use of the forelimbs and allow it more mobility and possibly more speed without needing a much larger tail or other such balancing requirements.

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  • $\begingroup$ Not necessarily crocodilian, Allosaurus had fairly large arms. $\endgroup$
    – John
    Dec 10, 2021 at 10:30
  • $\begingroup$ @John True, but it wasn't as large as the t-rex and its head-body ratio wasn't as sqewed towards as larger a head either, so it could afford bigger arms. They might even have been a little necessary for offensive capability since its bite wasn't as strong. $\endgroup$
    – Lemming
    Dec 10, 2021 at 10:32
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is there a good reason not designing this once an apex predator of it's time to have a bigger and stronger arm that can actually do serious damage to building structures and vehicles?

Because it wouldn't be a T-rex.

They'd probably be better off starting with a different base creature like the Acrocanthosaurus.

EDIT

You're not going to evolve a dinosaur to meet the needs of a sortie. Instead, you're going to pick the correct nightmare from the get-go.

If you need to knock down some brick-and-mortar buildings, you'll probably start with an an Ankylosaurus.

If you need to mow down an army of foot soldier, an Acrocanthosaurus with GAU-12s strapped to each arm might work.

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  • $\begingroup$ It also has small arms ;D $\endgroup$
    – user6760
    Dec 10, 2021 at 13:51
  • $\begingroup$ @user6760 - I enhanced my answer. If you need to, feel free to post a new question regarding "which dino?" for a specific mission (and other constraints). $\endgroup$ Dec 10, 2021 at 19:52
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The T-rex lived and thrived with its short arms, despite all the memes that we see today, and as the saying goes "don't change a winning team".

Adding heavier arms would require redesigning the whole body, because it would alter its balance with an heavier front part.

If you want to increase its damage capabilities, focus on its strong points, like the bite, or exploit that long tail as a whip, which seems already much more use-ready than the forearms.

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  • $\begingroup$ I'm worried the tiny arms might actually be an Achilles' heel, the arms are so tiny the poor dinosaur would struggle to even get off the ground should it fell down ;D $\endgroup$
    – user6760
    Dec 10, 2021 at 6:56
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    $\begingroup$ @user6760, if it lived for some million years it should have found a way to stand up after a fall $\endgroup$
    – L.Dutch
    Dec 10, 2021 at 6:59
  • $\begingroup$ I suspect it can take it's own sweet time to recover from a fall because there is no immediate threat due to it's big body size ;D $\endgroup$
    – user6760
    Dec 10, 2021 at 7:03
  • $\begingroup$ @user6760 remember how big a rex is, if it falls down getting up in a timely fashion is the least of its worries. $\endgroup$
    – John
    Dec 10, 2021 at 10:31
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Your scientists did give the T-rex bigger arms, but they turned out to be an extreme danger during transport.

When soldiers strapped down the animal for transport, it was considerably harder to do with the extra large arms. These arms inevitably escaped or broke the restraints and several soldiers were killed trying to re-restrain the arms. These larger arms were also able to reach the harnesses for the head and legs, so were able to break these restraints as well. Three Chinooks, two C-130's, and even one LCAC were lost (in separate training accidents) due to the animals being able to get free.

The regular arm size was plenty strong, but small enough to be easily secured during transport. The smaller arms were also unable to reach any of the other restraining harnesses. The animals were also somewhat more docile with the smaller arms.

The larger arms seemed to confuse the animals, flailing them wildly around at times, causing harm to other animals, themselves, people, equipment, and buildings. Some animals even ended up dying after they chewed off their own limbs, or as much as they could reach. Since the animals wouldn't let anyone approach to tend to the wounds, they simply bled out. In the cases where they did this within a herd, the injured T-rex would end up getting attacked and eaten by the other animals, even before they died. This would sometimes end in a "feeding frenzy", where multiple animals ended up dead.

The scientists aren't sure if this was because of the presence of blood or because they would thrash around, injuring and angering the other animals.

Even when the animals survived to adulthood, went through training, and made it to deployment, they often turned against the soldiers releasing them from the restraints. The smaller armed animals needed less restraining, so were less likely to turn on their captors.

Due to the large armed animals' tendency to escape or turn on the people who released them, the idea of dropping the animals into a hostile area on it's own was considered. Unfortunately, all attempts to implement this ended in failure. Either the animal died on the impact of landing, were so dazed after landing they couldn't escape the container, or they attacked the container instead of the OPFOR. Even when the animal wasn't killed on landing, they were killed shortly afterwards with few enemy casualties.

With the extreme cost and low probability of being able to use these modified animals effectively in combat, a review board was convened. Further research was cancelled due to the unacceptable injuries, loss of life, and loss of material involved.

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What makes T-Rex The Tyrant King is the head. Everything the beast is is centered around the beast's bite. The size / mass of its head is everything. It's built like a Bulldog, where other "larger" predators are built like wolves. If you have ever seen or read "White Fang", the wolf dog defeats all comers until it encounters a bulldog.

T-Rex is a crusher, not a ripper. Its teeth are made like railroad spikes, not blades. In Jurassic Park, where it fought the Spinosaurus, the fight would have been over when it got its jaws around the spinos' neck the first time. If you do anything to T-Rex, give it stronger teeth...

If you move mass away from the head you depreciate the potential for its main weapon. Now if you are going to strap on guns and artillery to this thing I doubt its hands or jaws will matter much in that case.

Also, if you increase the arm size or strength, you need to increase the size and mass of the surrounding muscles' bone and connective tissues as well. Not just bigger arms.

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  • $\begingroup$ The A-10 of dinosaurs ;) $\endgroup$
    – Mazura
    Dec 11, 2021 at 9:16
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T-rex is too stupid to use arms.

Slap a pair of gnarly arms on a T-rex and you get the perfect killing machine? Nope -- you just get a T-rex with a pair of big dangly gnarly arms.

It is a simple matter to make the arms larger. But this creates more problems:

(a) Redesigning the muscles, ligaments to make the arms usable as weapons. Otherwise you just get a pair of big dangly vestigial arms.

(b) Redesigning the brain with nerves that connect to the new arms.

(c) IMPORTANT. Redesigning the brain so the animal naturally uses its arms. The T-rex brain is designed to control an animal without arms. You cannot just slap on bigger arms and expect it to know how to use them, any more than you can slap on an extra pair of legs and expect them to do something.

Perhaps more intelligent animals might figure out how to operate new body parts. . .

enter image description here

. . . but not something with such a teeny tiny brain to begin.

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Because your scientists don't know how to make the alterations without managing the possibility of defects.

Genes are more complex than they may seem. A single gene can code for multiple proteins that define how multiple biological systems operate, just as drugs often have unintended "side effects."

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Depending on the world your Dino is "working" on, adding to overall muscle mass might be a big problem. T-Rex for example lived in the Cretaceous Period. One issue with giant dinos in the modern day is, to the best of our estimations the O2 levels during the Cretaceous Period were about 40% higher.

To field a prehistoric creature today would require them to be scaled way down or potentially receive some sort of Cardio/Respiratory upgrade.

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Because, in addition to Jurassic Park, the scientists were also inspired by the Malazan Book of the Fallen and wanted to create K'Chain Che'Malle.

They just planned on fusing giant blades on the arms.

enter image description here

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