A Titanosaur That Weighed 75 Tons Was the Biggest Dinosaur to Ever Live, Scientist Says

What was the largest dinosaur—and by extension, the largest land animal—that ever existed? This question has been hotly debated by scientists in recent years, and now, a study has been published lending support to the idea that an enormous dinosaur known as Argentinosaurus, which lived between around 100 million and 90 million years ago, should regain its crown.

The animal was first described in the early 1990s after several giant bones were found in Argentina and it was long considered to be the most massive member of Sauropoda, a group of four-legged, herbivorous dinosaurs with long tails and necks that were the largest terrestrial creatures ever to roam the Earth.

However, in 2017, a team of scientists described another giant sauropod dubbed Patagotitan, also from Argentina, estimating that it had a body of mass of 69 tons, according to one method used in their study, although they also provided other figures. By some estimates, a body mass of 69 tons would have made Patagotitan around 10 percent heavier than Argentinosaurus.

However, independent paleontologist Gregory Paul, author of the Princeton Field Guide to Dinosaurs, has tried to shed new light on the debate by testing various body mass claims of the largest known sauropod dinosaurs for a study published in the journal Annals of the Carnegie Museum.

"As soon as I saw the paper on Patagotitan claiming that it was the largest I was very suspicious, and a comparison of the size of the dorsal vertebrae and the femora quickly showed that their conclusion was definitely in error, Argentinosaurus having been a bigger animal," Paul told Newsweek.

Many of the largest sauropods, such as Argentinosaurus and Patagotitan, belong to a subgroup called Titanosauria.

"There are a few other South American titanosaur bones that may indicate beasts as big as Argentinosaurus and bigger than Patagotitan. The conclusion that Patagotitan was the very biggest was controversial from the get-go, but no one else addressed the issue in the technical literature."

Argentinosaurus
Stock image: Artist's illustration of Argentinosaurus. iStock

Since the 1980s, Paul has been producing rigorous skeletal restorations of dinosaurs, and from these, creating clay models that are immersed in water to measure their volume. The finding is then used to come up with an estimate for the dinosaur's mass.

"I still use the old technique and it produces results at least as accurate as the digital methods, perhaps better. I emphasize that attempts to eliminate the human skill factor from mass estimates are errant because at some point or other restoring the volume of dinosaurs requires a high level of anatomical skill," he said.

In the latest study, Paul used these techniques to estimate the masses of the biggest dinosaurs known to science. He found that the largest dinosaur by body mass was indeed Argentinosaurus, estimating that it had a mass of 65-75 tons.

In his analysis, Patagotitan came in second with an estimated mass of 50-55 tons, which is close to some of the estimates that the original describers of the dinosaur came up with when they used similar volumetric modeling techniques. The figure of 69 tons that the Patagotitan's describers included in the 2017 study was the result of digital methods.

Many titanosaur specimens, including Argentinosaurus, are very incomplete, which makes it difficult to produce reliable body mass estimates. However, the discovery of more complete titanosaurs in recent years, such as Patagotitan, Dreadnoughtus, and Futalognkosaurus, have helped to provide a framework for the proportions of these giant animals.

"Because Patagotitan and some other remains have made it possible to reasonably reliably restore the form and volume of giant South American titanosaurs, we now have a very good idea of their relative masses, and Patagotitan is beyond reasonable doubt neither the biggest, nor in the area of 70 tons as per one estimate in the original description," Paul said.

"That was based on extrapolating from limb bone strength factors, which I and many others have long explained are very unreliable, producing results in living animals that vary by as much as a factor of two, and statistically must produce even more variation in extinct forms. Although not perfect, volumetric models have an error of around 15 percent plus or minus. The paper is the first to give solid relative and absolute values for super titanosaur masses that within the plus-minus errors inherent to the method are unlikely to change much over time."

Paul does note in the study that Pataogotitan is currently the largest dinosaur known from most of the skeleton, albeit that of more than one individual.

According to the study, the less complete, fragmentary specimens of Notocolossus, Puertasaurus, and Antarctosaurus giganteus indicate that these dinosaurs occupied a similar size range to Pataogotitan. Meanwhile, another dinosaur, Paralititan, likely weighed between 30 and 55 tons.

Meanwhile, Dreadnoughtus, Alamosaurus and Futalognkosaurus were in the area of around 30 tons, although the former is only known from a juvenile specimen so its mass was likely significantly larger.

"As the paper notes, the biggest land animal known from a single, nearly complete skeleton is the good old Carnegie Museum Brontosaurus (or Apatosaurus) at around 20 tons," Paul said.

Despite the huge size of dinosaurs like Argentinosaurus and Patagotitan, the study notes that there is one mysterious animal that may dwarf them all: the near-mythical Maraapunisaurus. This dinosaur is only known from a single drawing and measurements of a gigantic vertebrae bone described in the late 1870s by the famous American paleontologist Edward Cope.

Unfortunately, the fragile bone—which according to Cope's measurements was a staggering 8.8 feet long—is now lost, with some experts speculating that severe deterioration caused it to disintegrate, given that the paleontologist didn't use any hardeners or preservatives, which were uncommon at the time.

Many doubt Cope's description of Maraapunisaurus, which is not a titanosaur, but rather another type of sauropod called a diplodocoid. However, if his measurements were accurate, they would suggest that the dinosaur had a mass of 80-120 tons, according to Paul, making it far bigger than even the largest known titanosaurs.

"Maraapunisaurus appears to have been an actual and very large sauropod, probably exceeding the titanosaurs. I give some very broad estimates in the paper, we never will really know unless more remains are found," Paul said.