Scientists have discovered the fossilized remains of a new long-necked, long-tailed dinosaur that has taken the crown for largest terrestrial animal with a body mass that can be determined accurately.
Measurements of bones from its leg and arm revealed that the animal was 65 tons and still growing when it died in the Patagonian hills of Argentina about 77 million years ago.
“To put this in perspective, an African elephant is about 5 tons, T. rex is 8 tons, diplodocus is 18 tons, and a Boeing 737 is around 50 tons,” said study author and paleontologist Kenneth Lacovara at Drexel University. “And then you have dreadnoughtus at 65 tons.”
Dreadnoughtus, meaning “fears nothing,” is named after the impervious early 20th century battleships. Although it was a plant-eater, a healthy dreadnoughtus likely had no real issues with predators because of its intimidating size and muscular, weaponized tail.
Its enormous bulk also had a downside. Based on the width and strength of its skeleton, toppling over likely would spell death for such a heavy animal.
“If you look at its really big ribs, there’s no way they’re going to withstand 65 tons of weight on top of them,” he said. “It would have been a catastrophic event in the life of a dreadnoughtus if it fell over.”
However, it probably didn’t do much walking. Its 37-foot-long neck could already provide access to a wide bounty of vegetation.
“How do you come up with a body size that is so enormous when you’re a terrestrial animal?” said Luis Chiappe, director of the National History Museum of Los Angeles’ Dinosaur Institute, who was not involved in the study. “You need to have a structural design that allows you to support a body like that, and you have to be potentially adapted to eat 24 hours a day, nonstop, with a minimal amount of sleep.”
The study was published online Thursday in Scientific Reports.
On the first day of the 2005 field season in southern Argentina, Lacovara spotted a lump of bone sticking out of the ground. It was maybe the 20th fossil he had found that day, so he didn’t think much of it. As he kept digging, he realized it was a massive dinosaur femur that stretched more than 6 feet long.
Lacovara still wasn’t all that thrilled until more and more pieces started popping up. By the end of that first day, he had added a tibia, a fibula and a half-dozen tail vertebrae.
“At that point, I’m pretty excited,” he said. “But I had no idea that we were going to walk away with 130 bones.”
The huge creature also had a smaller companion, which Lacovara and his colleagues also dug up. Both got caught in quicksand, which is how their bones became so well-preserved.
The skeleton of Dreadnoughtus schrani is remarkably complete for a dinosaur of this size — more than 70 percent of the bones were dug up, excluding the head. Typically long-necked, long-tailed dinosaurs have tiny skulls, so those bones don’t survive.
There might be more massive dinosaurs out there than dreadnoughtus, but their masses can’t be accurately calculated without the humerus and femur, which tend to correlate well with an animal’s weight.
The previous contender for biggest land animal with a mass that could be determined by bone circumference was called titanosaur, or Elaltitan lilloi
. It was estimated at 47 tons.