This episode is brought to you by  the Music for Scientists album, now available on all streaming services.

To start listening, check out  the link in the description. [♪ INTRO]. Tyrannosaurus rex has been  everyone’s favourite dinosaur for more than a hundred years.

And a century of study has given us new  insights into what this terrible lizard looked like, and the role it  played in the Cretaceous world. But even though we’re learning more all the time, the popular image of T. rex  seems to be stuck in the past.   Now, new techniques and new fossils  are turning our thinking about these fearsome predators on its head. It’s time to meet the real T. rex!

Skeletons of this gigantic dinosaur were  first discovered back in the early 1900s. The first paleontologists that studied  them saw rows of deadly sharp teeth and long powerful legs, and rightly  concluded that they belonged to a fearsome predator. This dinosaur, Tyrannosaurus rex,  lived about 68 to 65 million years ago, at the end of the Cretaceous period.

It was one of the biggest  land predators of all time. Since then, T. rex has been immortalized in books, films, and cuddly plushies,  as the iconic dinosaur. But if you ask anyone to actually  draw a T. rex from memory, they’re a big chance that most  will draw it Godzilla-style upright and balanced on its tail, with its little arms tucked  uselessly next to its chest.

The first T. rex skeletons were  actually mounted in this way, and nobody questioned it for a long time. But the discovery of new fossils and  a renewal of interest in the 1970s led to a so-called ‘dinosaur renaissance’, which transformed how we  see these ancient creatures. Scientists reanalyzed the skeleton of T.  rex, and saw that it was much more likely to have a horizontal spine, with its  back flat and its tail in the air.

After this, museum skeletons were remounted, illustrations were updated in  science books, and even popular films like Jurassic Park showed T. rex  as an agile, crouching hunter. But studies have shown that  many people still get it wrong. Researchers think that it’s because there’s  still so much kitschy stuff out there, like cookie cutters and stuffed toys,  that have the out-of-date upright posture.

Nevertheless, there’s been more  than a hundred years of paleontology since T. rex was discovered, and new techniques have taught us a  lot about what they’re really like. For one, it looks like their tiny  arms might not be totally useless. Sure, T. rex does have comically  tiny arms, and for a long time scientists wondered how they  could do much of anything.

But paleontologists speaking at  a conference in 2018 presented some evidence that they were more flexible  and useful than previously thought. The researchers used X-ray imagery and  computer models to look at the joints of some of T. rex’s modern relatives --  specifically, turkeys and alligators. Their research hasn’t been published yet,  but they propose that those tiny arms could actually have brought  prey in close for a bite.

However, while its arms may have  been better than we imagined, its legs are a bit of a letdown. T. rex’s long, sturdy leg bones  have been used in the past to argue that they could run fast, like an ostrich. But because the muscles and tendons  that actually do the running aren’t preserved in the fossil record,  estimates haven’t been very precise.

You can’t just guess based on  a smaller animal scaled up, because big animals like T. rex put  proportionally way more strain on their bones and muscles, compared to smaller ones. Using different methods, scientists  have suggested top speeds that range from eighteen to more  than seventy kilometers per hour. That’s a bit of a mixed bag.

A study in 2017 took a new approach,  combining biomechanical simulations with measurements of stress on the skeleton. This revealed that if they even tried to run, it would put too much force on their  leg bones, causing them to fracture. So T. rex was probably limited to a  fast walk, or a birdy sort of jog.

Basically, it works out to a maximum  speed of about thirty kilometers per hour. That means an Olympic sprinter  would easily be able to outrun one! Though… not for very long.

Also it means I definitely couldn’t. While new techniques are giving  us insight about old fossils, new fossils are turning up  that change our thinking too. Which brings us to the feather question.

In the last few decades, remarkably  preserved fossils are revealing that all kinds of dinosaurs had soft, downy  feathers, including relatives of T. rex. Dilong paradoxus, a small ancestor of T. rex, was discovered to have simple  proto-feathers in 2004. And the nine-meter-long  Yutyrannus, described in 2012, is the largest feathered dinosaur discovered yet.

It was previously thought that only  the smaller dinosaurs had feathers, because small bodies tend to need  more insulation than big ones. But huge fluffy Yutyrannus made us think again. Soon, the idea of feathered bodies  expanded to include all tyrannosaurs, including T. rex, because  scientists think a trait like that isn’t easily lost by evolution.

But a study in 2017 analysed  brand new fossils of T. rex skin, which were scaly, not feathered. These two conflicting points of view  have sparked intense debate among paleontologists, intense enough that,  like, we don’t want to get into it. But this is definitely a mystery  we won’t be able to solve for sure until we have more fossils.

We don’t know for sure, but  it’s possible that baby T. rex may have been born fluffy, with  insulating feathers over their bodies. Adults could have retained a few  feathery bits here and there, but the matter is far from settled. In a way, though, that’s exciting.

It shows how much there still is to learn  even about something we think we know well like this familiar staple of  every six-year-old’s toy chest. Who knows what we’ll learn  in the next hundred years? In retrospect, it’s easy to poke fun at those old, incorrect museum mounts of  T. rex and other dinosaurs.

But science is a process of sifting through ideas and discarding the ones that  don’t hold up to experimentation. These ideas, right and wrong,  are celebrated in the song. The Idea from the album Music for Scientists.

The song also has an original music  video that fuses original artwork and machine learning -- just  like the whole album ponders the intersection of art and science. If that sounds like it might be your jam, you can start listening to Music for  Scientists at the link in the description. [♪ OUTRO].