A 6 foot heart and eyes the size of tennis balls… Meet the largest creature to ever walk the earth

As the gentle giant grazed in the steaming humidity of a prehistoric forest, it must have sensed a fraction too late that it was being pursued by a bloodthirsty rival. Standing 26 feet tall – almost twice the height of one London bus – and measuring 121 feet from nose to tail, Patagotitan mayorum weighed an earth-shattering 65 tons, which was as much as nine African bull elephants.

But even though its assailant, the deadly Tyrannotitan, was a third its size, the 60 sharp teeth in its powerful jaws could tear through flesh in seconds. Suddenly it pounced and bit its quarry’s tail.

During the almighty encounter between these heavyweights of the dinosaur world, it looked like the Tyrannotitan’s herbivorous victim might have nibbled its last leaf, but it had a secret weapon in its enormously powerful, 52-foot-long tail.

Filling the air with fearsome snarls and roars, it thrashed back and forth until the Tyrannotitan was finally knocked away, leaving its intended victim dripping with blood but surviving to graze another day.

Exactly when or how the Patagotitan, which was the largest of all known dinosaurs, finally died, we do not know.

But now, some 100 million years later, a replica of its colossal skeleton is going on display at the Natural History Museum in London – complete with a dent in one of the vertebrae believed to have been a bite mark left by Tyrannotitan.

The largest known creature to walk our planet will dwarf the museum’s other giant attractions – it’s more than four times heavier than Diplodocus Dippy and 40 feet longer than Hope the blue whale.

“It’s absolutely amazing for its scale,” says the museum’s dinosaur expert Professor Paul Barrett.

The exhibit, which opens next March, also includes the skull of a Tyrannotitan, the creature believed to have attacked Patagotitan.

Of course, we can’t be sure of this, but it seems like the most likely contender in the hostile primordial environment they both inhabited.

They lived in the Cretaceous period between 66 and 100 million years ago in a region corresponding to present-day Argentina.

The story of the remarkable skeleton that came to the Natural History Museum began in 2014, when an Argentine shepherd, searching for a lost member of his flock, stumbled upon a huge femur sticking out of the ground.

At 8ft long, this cartoonishly large femur looked like something out of The Flintstones.

The scientific name of this new species was inspired by the region where it was discovered, Patagonia, and its strength and large size, with the Titans being the powerful Greek gods said to have ruled before the Olympians.

Over the next two years, another 200 bones were discovered, revealing that at least six of these giants had died in what was once a floodplain near a river.

The growth marks on the bones, which can be read much like the rings on trees, suggested that these were young adults in their teens or early 20s. It is not clear whether they were men or women.

Since none of the skeletons were complete, paleontologists used fiberglass replicas of the bones to construct a composite skeleton so large that it had to be pieced together in a cave warehouse.

While the original fossils remain in Argentina, demand from museums around the world to display replicas has been such that multiple copies of the skeleton have been made.

Exactly when or how the Patagotitan, which was the largest of all known dinosaurs, finally died, we do not know. Pictured: Life-size model in Patagonia

When Patagotitan makes its European debut next year, it will barely fit into the Natural History Museum’s Waterson Gallery – despite its 30ft high ceilings. In fact, the skeleton is so large that visitors will be able to walk underneath it.

‘You only get up to your ankles when you stand next to it,’ says Professor Barrett. ‘This is an animal that really towers over you and it’s quite humbling.’

The dimensions of its bones were crucial to estimating Patagotitan’s size and weight, suggesting that it had reached the upper limits of how large land animals can get before their skeletons are unable to support them.

Amazingly, these giants hatched from eggs only about 8 in diameter – smaller than a football.

The females laid as many as 40 of these at a time to increase the chances that at least some of them survived, probably using rotting leaves to aid incubation. Once hatched, the offspring were highly vulnerable to predators, including the pterosaurs, fearsome flying reptiles with large wingspans that scanned the ground for prey to pounce on and devour.

Apart from these and the Tyrannotitans, these young would also have lived in fear of the Giganotosaurus, ten-ton carnivores that bared 8-inch-long teeth, walked on two legs, and could reach 30 mph—far faster than the Patogotitan’s stately 5 mph on all fours.

To help avoid detection, their scaly crocodile-like skin was likely brown or gray. “We can’t be sure about this, but if you think about the largest land animals today, like elephants, they tend to be dull colors that help them blend into the landscape as a form of camouflage,” says Professor Barrett.

As the Patatogytans grew older, predators would have been intimidated by their enormous size and the fact that they traveled in packs.

They also enjoyed a high vantage point over the world. Stretching 45 feet, their necks were eight times longer than the average giraffe and consisted of 15 enormous vertebrae, about six or seven times longer than they were wide. And with eyes the size of tennis balls set into their tiny heads, they could see potential attackers coming, even though they couldn’t cause much damage with their tiny, stick-like teeth.

These suggest that they were fairly well-behaved eaters – they took small bites rather than tearing at the vegetation. Still, they got through about 440 pounds of food a day, and while they dined on conifers and ancient relatives of monkey puzzle trees, they could also reach down to eat the ferns that dominated before grasslands developed.

Since this diet was very fibrous, their intestines would have been extremely long, and the food took up to ten days to be digested and pass through it. As it fermented in their large bellies, huge amounts of methane would have been produced as a by-product.

The dimensions of its bones were crucial to estimating Patagotitan’s size and weight, suggesting that it had reached the upper limits of how large land animals can get before their skeletons are unable to support them

“I have a strong suspicion that the back end of a Patagotian herd was not a place you would want to be,” says Professor Barrett.

Their long stomachs were just one of many extraordinary biological adaptations that helped the patagotitans survive.

Essentially the size of moving houses, one of their biggest challenges was getting oxygenated blood pumping around their enormous bodies. To achieve this, the Patagotitans would need hearts at least 6 feet in circumference. Weighing three times as much as a grown man, they could have moved about 158 ​​pints of blood in a single stroke.

As with some birds, the dinosaur’s closest living relatives, the Patagotitans’ breathing is also thought to have been aided by huge air sacs, which took up much of their chests and ran the length of their bodies from the tailbone up through the very long neck to the head.

Connected to their lungs, these helped them take in oxygen continuously as they breathed in and out.

To reduce weight, their bones were full of holes – a bit like Swiss cheese. And as they lurched forward on all fours, their huge, column-like legs spread out slightly, supporting their bulk. Markings on their femurs where the muscles were attached suggest that their hind legs were connected to their tails, bringing the hindquarters up and forward to help propel the Patagotitans forward.

These weird and wonderful miracles of bodily construction are believed to have had a lifespan of about 50 years.

There is one question that the Natural History Museum’s exhibition will not be able to answer: why did the young that were found near that watering hole die prematurely? Some experts have suggested that they were isolated from their group and died of stress and starvation; others that a volcanic eruption covered the surrounding vegetation, resulting in their starvation.

While we should count ourselves lucky that we’ll never come across a Tyrannotitan or a Gigantosaurus, the upcoming exhibition in London will certainly bring us one step closer to imagining what it was like when creatures like the massive but meek Patagotitans roamed the earth.