WASHINGTON – Scientists have unveiled estimates of body weight for an astounding 426 dinosaur species using a formula based on the thickness of their leg bones, crowning the long-necked Argentinosaurus as the all-time heavyweight champ.
That plant-eating dinosaur weighed an earth-shaking 90 tons when it lived about 90 million years ago in Argentina. It is the largest known land creature in the planet’s history. Blue whales, the largest animals ever, can weigh up to 170 tons.
“Argentinosaurus, that’s the champion,” Oxford University paleontologist Roger Benson, who led the study, said in an interview. “It’s colossal.”
In their dinosaur “weigh-in,” the scientists included birds, which arose roughly 150 million years ago within a group of feathered dinosaurs called maniraptorans. The distinction of being the smallest dinosaur ever went to a sparrow-size bird called Qiliania, which lived about 120 million years ago in China and weighed a mere 15 grams.
Benson noted that Argentinosaurus was around 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 journal PLOS Biology.
The largest meat-eating dinosaur was Tyrannosaurus rex, which weighed 7 tons and is the largest known land predator of all time. The T. rex edged out another predator, Giganotosaurus, which some scientists had figured was bigger based on the length of its skull. Giganotosaurus lived alongside Argentinosaurus in ancient South America.
The study estimated Giganotosaurus at about 6 tons — just a bit shy of dethroning T. rex.
Dinosaurs had a remarkable run. 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 — all but the birds, that is.
The mass extinction at the end of the Cretaceous, caused by an asteroid that hit Mexico, doomed most creatures, although 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 tanklike 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 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 noted 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.
More than 1,000 species of dinosaurs have been identified, but many are known from only fragmentary 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 was based on the relationship between the robustness of the limbs and the weight of the animal, the researchers said.