The biggest known terrestrial animal was the peaceful and plant-loving Patagotitan mayorum, a newly analyzed and named dinosaur that weighed nearly as much as the Space Shuttle.

Credit: Jorge Gonzalez

In the distance, he suddenly saw what appeared to be a giant bone. Wondering what had died, he showed the bone to his boss Oscar Mayo, a dinosaur buff who suspected that the remains belonged to a prehistoric animal. Other discoveries had been made in the region over the years, leading to Mayo’s suspicions.
 
Mayo contacted the nearby Museum of Paleontology Egidio Feruglio (MEF), which sent a team to the site. Multiple excavations followed, yielding a minimum of six dinosaur skeletons.
 
Subsequent analysis of the fossils, outlined in the journal Proceedings of the Royal Society B, determined that the remains belonged to the world’s largest known dinosaur, which has been named Patagotitan mayorum after the Mayo family, Patagonia and “titan,” a word from Greek mythology that refers to a powerful race of gods.

“As far as can be tested, Patagotitan is the largest dinosaur discovered so far,” lead author José Carballido of the MEF said. “We estimated its total length to be about 40 meters (131 feet). Our histological analysis, made on long bones (femura, humeri), indicates that the animals were still growing, but very slowly.”

Credit: Museum of Paleontology Egidio Feruglio

The dinosaur’s estimated body mass, based on a circumference equation utilizing the same bones, was 69 tons, which is about 10 tons less than the weight of the entire Space Shuttle. The animal, identified as a titanosaur, lived approximately 101.6 million years ago, according to Carballido and his team.

Titanosaurs were the last group of sauropods to evolve. These were four-legged, small-headed plant-eating dinosaurs with long necks and tails. They tended to be very large.
 
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Argentina was home to several such dinosaurs, including Argentinosaurus and Puertasaurus. In the past, some of these dinosaurs were regarded as having been the world’s largest, but their bones were either smaller than those for Patagotitan, or there were not enough remains to permit proper size estimates.
 
The dinosaurs all lived in a lush, relatively warm environment.
 
“We have records in the same area of large conifer trees, flowering plants, ferns, and the remains of large carnivorous dinosaurs such as Tyrannotitan, as well as turtles, crocodiles, and primitive lizards,” co-author Diego Pol of MEF said. “So, this area probably had a temperate and humid climate, with meandering rivers.”

Credit: J. Farfaglia

It is doubtful that Tyrannotitan often attacked peaceful, plant-loving Patagotitan, given the herbivore’s tremendous size.
 
“The larger an animal is, the less probable it is that a (non-human) carnivore will try to attack it,” Carballido said. “This is especially true for ‘young adults,’ as the specimens of Patagotitan are. Attacking an animal of such big dimensions poses very large risks, and any carnivore would prefer to search for other prey.”
 
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If Tyrannotitan had tried to wage an attack, Patagotitan likely could have felled the meat eater with a tail whack or by stomping with its strong, thick legs.
 
No other known terrestrial animal — extinct or presently alive — matched Patagotitan’s size, so this dinosaur might represent the upper size limit for what is possible for life on land. While the found Patagotitan individuals could have grown even larger, the paleontologists do not think such additional growth would have been significant.

Credit: Alejandro Otero

Marine life is capable of growing to even larger sizes. Modern blue whales, for example, can weigh around 150 tons.
 
Water might have played a role in the death of the six excavated dinosaurs. They were all found by what was once the floodplain of a river. The authors say that dinosaur remains are often unearthed in such areas, as dinosaurs were probably attracted to the water and nearby vegetation, as many animals are today. It remains a mystery, however, as to what led to the demise of the dinosaur giants.
 
Another mystery concerns why Patagotitan and other titanosaurs grew to such enormous sizes. More primitive dinosaurs within the lineage were around 15–20 tons, which is a medium size for a sauropod.
 
“I am sure that we will learn more about this particular time in the history of the planet through the research that we and others are currently conducting,” Pol said.
 
A cast of newly named Patagotitan is now on display at the American Museum of Natural History in New York. Since the skeleton is too long for the museum’s space, the dinosaur’s neck and head extend out toward the elevator banks, welcoming visitors to the dinosaur floor. 

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