Thursday, 15 May 2014 | MYT 2:40 PM

Meet Argentinosaurus, heaviest vegetarian that ever lived

After analysing the leg bones of 426 different dinosaurs, scientists crowned Argentinosaurus as the ultimate heavyweight champ, estimating its weight at almost 82,000kg.

If you think you have a weight problem, spare a thought for Argentinosaurus, whose claim to fame was confirmed on May 6 when scientists named it the heaviest animal to have ever walked on land.

The plant-eating dinosaur weighed an earth-shaking 90 tons (81,646kg) when it lived about 90 million years ago in Argentina. It is the largest known land creature in the planet’s history. For comparison, the largest animal ever, the blue whale, comes in at 190 tons, or 172,365kg. (The 2014 version of Godzilla, meanwhile, comes in at 120,000 tons – but it's not a real animal despite its many movie incarnations.)

Giant among giants: Argentinosaurus, the largest animal that ever walked on land, can be seen above in an artist's illustration produced for the 2013 BBC documentary Walking With Dinosaurs, and a near life-size replica of it at the Weizmann Institute of Science in Israel.

“Argentinosaurus, that’s the champion,” Oxford University paleontologist Roger Benson, who led the study, said in a telephone interview. “It’s colossal. Scientists unveiled the unbelievable estimated body weight for Argentinosaurus together with estimates for 425 other dinosaur species using a formula based on the thickness of their leg bones.

Skeletal grandeur: A reconstruction of Argentinosaurus' fossil at Naturmuseums Senckenberg, in Germany (above), and an incomplete fossilised femur of an adult Argentinosaurus at Museo de La Plata, in Argentina.

In their dinosaur ‘weigh-in’, the scientists included birds, which arose roughly 150 million years ago within a group of feathered dinosaurs called maniraptorans. A sparrow-sized bird called Qiliania that lived about 120 million years ago in China earned the distinction of being the smallest dinosaur, weighing a mere 15g.

Benson noted that Argentinosaurus was about 6 million times the weight of Qiliania, and that both still fit within the dinosaur family. “That seems amazing to me,” added Benson, whose study was published in the scientific journal PLOS Biology.

The largest meat-eating dinosaur was Tyrannosaurus rex, which weighed 7 tons and is also the largest known land predator of all time.

T. rex edged out another super predator that some scientists had once figured was bigger based on the length of its skull, Giganotosaurus, which lived alongside Argentinosaurus in ancient South America. The study estimated Giganotosaurus at about 6 tons, pretty darned big, but just a bit shy of dethroning T. rex.

Dino legacy

Dinosaurs had a remarkable run on Earth. They first appeared about 228 million years ago during the Triassic period, achieved stunning dimensions during the ensuing Jurassic Period and then disappeared at the end of the Cretaceous Period about 65 million years ago. Only the birds, which evolved from maniraptorans, remain.

The mass extinction at the end of the Cretaceous, which most scientists think was caused by an asteroid that hit Mexico, doomed most creatures but some birds survived. Benson said this study underscores the reasons that birds made it while their bigger dinosaur brethren did not.

Other groups of dinosaurs such as long-necked sauropods like Argentinosaurus, the tank-like ankylosaurs, the duck-billed hadrosaurs, the spike-tailed stegosaurs and the meat-eating tyrannosaurs were essentially locked into a certain ecological niche. But birds filled all kinds of ecological niches with their widely diverse body sizes and 'occupations'.

Flying birds lived in all kinds of different habitats, both inland and coastal, and came in a wide range of sizes. But there also were large, ostrich-like flightless birds like Gargantuavis and flightless diving birds like Hesperornis.

“It might be that they were simply much more ecologically diverse and that could have helped them survive an extinction,” said Benson, who also noted that smaller creatures did a better job surviving the asteroid impact at the end of the Cretaceous.

Paleontologist David Evans of Canada’s Royal Ontario Museum said dinosaur body size evolved relatively quickly early on in their time on Earth as they invaded new ecological niches, but then slowed down among most lineages. The exception was the maniraptoran lineage that led to birds, Evans added.

More than 1,000 species of dinosaurs have been identified but many are known from only fragmentary fossil remains.

This study estimated the weight of every dinosaur whose remains are complete enough to contain the bones needed for the study’s formula, which is based on the relationship between the robustness of the limbs and the weight of the animal, the researchers said. – Reuters

Tags / Keywords: Lifestyle , Features , Science , Paleontology , dinosaur , Argentinosaurus , heaviest land animal , weight , Qiliania , Tyrannosaurus Rex , Giganotosaurus


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