We thought we knew the biggest dinosaur ever, but something else might have stolen its thunder

It seems T. Rex has probably been sensationalized too much. While the iconic carnivore has been the poster dino for the entire Jurassic Park franchise (except maybe that one Brachiosaurus), there were creatures that made it look like a pet lizard.

Titanosaurs trampled the earth from the Jurassic through the mid-late Cretaceous, leaving behind only fragments of their skeletons for scientists to try and piece together. These herbivorous species were so huge that even voracious predators like T. Rex would have to freeze literal tons of leftovers if freezers actually existed. Until recently, Patagotitan was thought to be the heavyweight, but researcher Greg Paul suggests there were more gargantuan things out there.

Paul, who published a study in Annals of Carnegie Museum, found that measurements of Argentinosaurus bones have an edge over those of Patagotitan, and there was possibly something that out-monstered both of them.

“A main conclusion of my analysis is that Patagotitan is definitely not the largest known titanosaur, that being the previously known, less complete titanosaur Argentinosaurus, the individual bones of which are distinctly larger in critical dimensions,” Paul, whose rendering of Argentinosaurus can be seen above and below, told SYFY WIRE.

While Patagotitan was previously thought to be the largest sauropod to have ever existed, Paul’s measurements resulted in an estimate of around 50-55 tons, while Argentinosaurus could have been an astonishing 65-75 tons. His mass estimates relied on volumetric models. These were based on restorations of the entire skeletal profile of the behemoth, which were then used to reconstruct it in three dimensions. Volumetric models are far more accurate than some other methods based on dimensions of individual limb bones. As a basis for comparison, models of extant animals that use the limb bone method are off by at least a factor of two—meaning, probably even more inaccurate in anything extinct.

Credit: © Gregory Paul 2020

But wait. Was there a size limit? Extreme life-forms have extreme energy needs, and these herbivores needed to munch quite a few trees to stay alive. They also have extreme limitations. The blue whale, which is now is the largest animal in existence at up to 82 feet long and 330,000 pounds, evolved during the ice age only a few million years ago, possibly because it feeds on almost unlimited plankton and that water alleviates at least some of the burden of its immense size. Scientists believe that physiological stress from diving and surfacing may have limited the blue whale’s body size.

“We know that sauropods approaching and perhaps exceeding 100 tons lived on land, in part because we have their trackways formed out of the water,” Paul explained. “The calculations show their bones were strong enough, and their muscles powerful enough, to have been able to walk normally.”

Super-titanosaurs are thought to have trudged along like elephants on land. The highest speed they could reach was probably no faster than 15 miles an hour, and it is unlikely something of that size could ever actually run. Not that they had too many predators to worry about. Growing to incredible sizes might have actually been how some titanosaurs adapted to living in places where their ancestors had always been stalked by theropods similar to T. Rex or Allosaurus. because trying to take down such a beast was useless for a carnivore, dagger teeth and all, whose average height was around 20 feet. Could anything have held these titans back from growing any larger?

“It is possible that limitations in finding food are what limited the size of sauropods. Or problems pumping blood all the way up to their heads. Or structural issues regarding moving on land,” Paul said, but stressed that “It is not known what the maximum size limit of animals is on land or in the water, or why.”

Even Argentinosaurus, which was proven to have been an overall larger species than Patagotitan, may have still not been the most massive sauropod and land animal to have ever roamed the Earth. Something may or may not have beat that. Maraapunisaurus, if it actually existed, is thought to have been at least 80-120 tons. This hypothetical dinosaur might have gotten to such a size because it had a shorter neck than Argentinosaurus, which relieved it of blood pressure issues often brought on by extreme height, and vertebrae that were built for a strength boost. The problem is that only one vertebra thought to belong to this mythic creature was ever found—and then lost.

Whether Maraapunisaurus was real remains a mystery. Unfortunately, even known species like Argentinosaurus and Patagotitan have only let us know of their existence through incomplete skeletons. That still doesn’t mean larger sauropods never made the ground tremble with their thunderous footsteps. Dinosaurs of such a tremendous size, as Paul noted, could not have been easily fossilized because decomposition processes probably didn’t allow for them to be buried fast enough for sufficient preservation.

“There are partial remains of other sauropods that may suggest animals larger than Argentinosaurus,” he said. “In any case, the possibility that we have happened to have already found the largest land animals of all time is essentially zero, bigger ones must have existed.”

Just don’t tell that to any hardcore Jurassic Park fans.