If the world's most notorious carnivore had survived the mass extinction that wiped out the dinosaurs 66 million years ago, it might have ended up losing its arms entirely.
The end of the season was fast approaching - the last chance to succeed in a very expensive expedition.
It was August 1902 and Barnum Brown led a team of paleontologists into the unusual, rolling landscape of Montana.
Among the high temperatures and in the crusted dust, they searched for fossils - digging into the golden-brown earth with chisels and pickaxes, setting aside small excavations in scattered locations, sometimes unearthing half-decent sites only to later abandon them.
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They urgently needed something good to send back to the American Museum of Natural History.
From his office in New York, Brown's boss was as impatient as his far-flung lieutenants.
Henry Fairfield Osborne recently received a shipment of their latest catch, a huge chunk of rock containing the skull of some kind of duck-billed dinosaur.
The shipment was driven 3.379 kilometers from the archaeological site - an arduous, risky journey that involved horses, railways and carrying heavy loads.
Only then did Osborn discover that the hidden fossil in the stone tomb was a shriveled, distorted mass.
The sample was hidden in the museum's basement, but he felt that it could have been thrown away immediately.
But now there is new hope.
Brown discovered a large number of bones of a large carnivorous dinosaur that was completely new to science.
His thigh bone was a meter and a half long.
This was a tyrannosaurus rex - the first ever discovered.
Brown had never seen anything like it.
In a letter to Osborne, Brown wrote: "There can be no doubt that this is a discovery of great scientific importance so far."
Little did he dream that it would actually be the discovery of the century - a discovery that would transform our understanding of dinosaurs and awaken public interest in these ancient creatures.
But from the very beginning, one aspect of these "tyrannical lizard" kings was utterly mysterious: their arms.
The t-rex skeleton lacked all the fingers and both forearms, which in early portraits were drawn with surprisingly accurate guesswork - prompting speculation that they couldn't be quite that short.
What could be their purpose? And how did they get so small?
It's bizarre that they were.
Today, the t-rex is almost as famous for its stunted arms as its enormous teeth - they are so disproportionate that they look like they were plucked from another species and simply stuck on this one, as some sort of tribute to the hilarious bone-assembling antics of the 19th century (like the the time the stegosaurus' dorsal plates were added to its tail).
“You'd look at his hands and say, well, this is ridiculous. They're too different from anything that exists today, what their purpose is," says LJ Krumenaker, a paleontologist at Idaho State University.
With arms just 0,9 meters long on a 13,7 meter tall individual, those tiny limbs of this fearsome carnivore have been the source of fierce speculation since they were discovered - despite decades of study, to this day, no one has any idea what they actually do.
Although Brown's t-rex was unearthed in 1902, it would be a long time before scientists got their first glimpse of its unusual arms.
The original skeleton contained little more than a modest selection of jumbled bones - among them was a pelvis, one shoulder blade, one upper arm bone and part of a skull.
Six years later, a fossil hunter discovered another specimen much farther south, in Big Dry Creek, Colorado.
It was an unusually perfect specimen, and its magnificent figure adorns the American Museum of Natural History to this day.
But that one also had no hands.
For most of the next century, scientists could only guess at what a t-rex's forearms might have looked like.
Much speculation was based on its cousin Gorgosaurus, another tyrannosaur that also roamed North America during the late Cretaceous period, about 66 to 101 million years ago.
And then, on September 5, 1988, rancher Kathy Wankel stumbled across an unusual bump in the ground near Fort Peck Lake in Montana—it was like the corner of an envelope, she later told The Washington Post.
Wankel didn't have time to make the discovery that day, but she didn't forget about it—she returned a month later and unearthed a set of long bones, which she drove to the Museum of the Rockies, hundreds of kilometers to the west.
The director of paleontology agreed to take a look.
They soon realized that these were no ordinary dinosaur fossils - they were the arm bones of a t-rex, complete with the mysterious lower half that had been missing for so long.
Eventually, the rest of the dinosaur was excavated, only to discover a 3.175-kilogram monster that was so perfectly preserved, it was still in its original dying pose, neck thrown back, like a dead bird.
It was a "Wenkel Rex" and its front limbs were even smaller than anyone had imagined.
A stunted little puzzle
Over the past century, scientists have discovered startling details about many aspects of the T-rex's life - from their slow, clumsy gait as they made their way through the swampy forests of the North American West, to their unfortunate susceptibility to a disease formerly associated with humans - gout.
Paleontologist Elizabeth Boutman and colleagues may have even glimpsed their original collagen preserved in some remarkable fossils.
Until now, the purpose of the dinosaur's short limbs has proved elusive - but it's not like various people haven't tried to figure it out.
One early idea came from Osborne himself, who gave the t-rex his name.
"He saw these very small, unusually tiny hands and compared them to the small fins present on today's sharks," says Scott Persons, chief curator of the Mace Brown Museum of Natural History in North Carolina.
Male sharks use those two fins at the base of their tails - claspers - to hold on to the female during mating, which can be a slippery task underwater (they're also used for the act itself).
"And so he envisioned a pair of tyrannosaurs entwined in a prehistoric embrace with the male from above using his arms to grab onto the female," Persons says.
Persons explains that it is perfectly possible that Osborne was right.
If male t-rexes - which are notoriously hard to find - had different hands than females, it would make sense that they used them for sex.
"But things didn't develop in that direction," he says.
Instead, as more and more individuals have been found - there are now at least forty - scientists have confirmed that they all have characteristically small hands, and they always look pretty much the same.
Another, potentially comical possibility is that the t-rex may have used its small arms to lift itself off the ground.
With bodies weighing up to 7.031 kilograms - equivalent to the weight of a large African elephant - it may not have been easy for them to maneuver out of a resting position or get back to their feet if they fell.
(Many animals still have trouble with this today, such as turtles, who often have to swing to right themselves when they end up on their backs.)
"And so when they got up from squatting, they could use their arms to do a little tyrannosaurus pushup," Persons says.
However, there's a small problem with that theory as well - this carnivore's hands wouldn't be much help at all.
“You have to be aware that it only helps the tyrannosaurus in the first half meter. And then he still has about five meters to rise from the ground," he says.
Another controversial idea, put forward by a lone scientist in 2017, is that adult specimens such as the Wenkel rex may have used the short arms as weapons - perhaps holding enemies in their jaws or pinning them to the ground with weight, before slicing and torn to pieces.
This idea is supported by the fact that, although short, the arms of the t-rex are surprisingly muscular.
He calculated that even with 0,9 meter limbs, those butchering movements could cause serious injury, creating wounds several centimeters deep and at least a meter long in just a few seconds.
"Now, I personally think those arms are too short to make sense," Persons says.
However, there is also the possibility that they had no function - the t-rex's small arms were the last remnants of once useful limbs that had long since ceased to be necessary.
If they were simply holdovers from another time, like a human tail, the world's most fearsome predator might have had an even more gruesome future: it would eventually evolve to lose its arms entirely, resembling some kind of fearsome land shark.
If the tyrannosaurus reign had not been interrupted by an asteroid impact, if we fast-forwarded the tape into the future, a theoretical five or even 20 million years ahead, do I think the tyrannosaurus arms would have continued to shrink? Yes," says Persons.
"Do I think that in the end they would disappear completely? I definitely think there was that possibility," he adds.
Persons explains that even if the t-rex didn't have a major function for its arms, any small purpose for them could have been enough to preserve them - even though they would have shrunk even more eventually.
This could have involved females using their hands to excavate the nest, as sea turtles do.
It could also have involved grooming, he suggests - packs of 13,7m tall monsters sitting in a circle gently stroking each other's feathers (because many paleontologists believe they were covered in them).
Scientists have found entire groups of fossilized tyrannosaurs in three different locations across North America, which some have interpreted as evidence that they were more social than we thought.
One team even proposed a collective noun for these gatherings: tyrannosaurus "terror."
Because of this, some experts have begun to speculate that these sociable t-rexes may have found their small hands useful during feeding frenzies.
If carnivorous dinosaurs ate in packs like carrion hyenas, gathering around the carcasses of triceratops and other giant contemporaries, it may have been awkward to keep larger hands out of the way of other people's jaws.
"This weird idea is that their hands were small enough that they didn't get in the way of all these guys fighting over food with huge mouths, so they basically didn't bite their own hands," says Krumenaker.
However, Krumenaker points out that it is usually difficult to test such ideas, in part because there are no analogous creatures alive today that would serve as easy comparisons.
"With a big head and tiny hands, the closest we can get is perhaps a ground-dwelling bird of prey.
An alternative is to use basic physics.
Intriguingly, but one of the latest ideas is that the dinosaur king's hands shrunk to this shortened form to serve a very important purpose - namely, there's a good reason why they had to get so tiny.
It is possible that their small hand size helped them to have as large a head as possible and a powerful bite: the intimidating silhouette of the average t-rex was no accident.
To understand why, it will help if you study their body structure.
Earlier this year, researchers discovered that another dinosaur—Merakses gigas, a 4.082-kilogram giant that inhabited Patagonia during the late Cretaceous period—had an unusually similar physique.
Although both dinosaurs are only distant cousins, both had huge bodies with oversized heads and extremely small hands.
The idea is that as the heads and bodies of raptors grew, their arms got smaller in proportion, perhaps to keep them balanced.
To help us understand why these proportions were necessary, it will help if we study their teeth.
It turns out that the t-rex's thick, conical teeth weren't like the piercing needles or razor-sharp sabers from the jaws of some other animals.
Instead, they are more like jagged bananas: sharp around the edges, but not at the ends.
"You can't cut yourself on the edge of a tyrannosaurus's tooth," says Persona, though he points out that you can on its edge.
That's because, instead of being mere meat cleavers, they're built to be powerful enough to break bones, crush huge prey, and tear off chunks that can be swallowed whole.
But this strategy requires serious strength—heavy teeth require a bulky jaw to withstand the pressure of a bite, which in turn requires a ton of muscle to keep it working properly.
In short, their heads and shoulders had to be huge.
"And that's potentially a problem. That's why all the carnivorous dinosaurs, from allosaurus to velociraptor, are built a bit like a seesaw - they have to stand on two legs," says Persons.
With a t-rex's huge head, larger arms would push the front end forward or require a larger tail to counterbalance.
However, it is also possible that we will never know the true function of the t-rex's arms.
Like discovering long-tubed passionflowers from North and South America without discovering hummingbirds that stick their long beaks into them, sometimes you need context to understand a function lost in the fossil record.
After more than 66 million years—during which volcanoes erupted and went extinct, islands formed and disappeared, and tens of thousands of species came and went—the nuances necessary to understand certain behaviors may have been irretrievably lost to be of any use.
All this interest in the unusual hands of an animal that became extinct 66 million years ago may seem strange.
But beyond the curiosity about something so addictively interesting, Persons thinks he knows why.
"We humans are perhaps a little too preoccupied with the importance of our own hands and our own hands, because they are so crucial to our own survival," he says.
As a primary way of interacting with our environment, it is difficult to imagine deliberately giving them up.
"And then we have this highly successful, highly intimidating animal that seems to want nothing to do with them at all," Persons says.
*Zarija Gorvet is a journalist in the rubric BBC Future
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