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Dreadnoughtus Was Probably Not the Biggest Dinosaur Ever

But the finding, and the science behind it, are incredibly exciting.
September 5, 2014, 6:40pm
An artist's rendering of Dreadnoughtus. Image: Jennifer Hall

Dinosaur fans around the world are going ballistic over Dreadnoughtus schrani, a new titanosaur discovered in Patagonia. A quick scan of the headlines would have you believe that the titanosaur, which weighed an estimated 65 tons, is the biggest dinosaur ever to walk the planet. Not so, my dinodudes.

At no point did anyone involved with the original study, published in Scientific Reports yesterday, claim that it had cinched the illustrious title of "biggest ever." The study merely said that Dreadnoughtus was the largest dinosaur (wait for it)…"for which a body mass can be accurately calculated."

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That may not sound as flashy as "biggest dinosaur of all time," but it holds much more scientific weight.

As I reported earlier this year, there are all kinds of massive sauropods (long-necks, to you Land Before Time fans) that theoretically outweigh well-documented species by a huge margin.

Based on a likely-fictitious femur and vertebrae from the giant sauropod Amphicoelis, for example, these animals might have tipped the scales at 135 tons, well over twice Dreadnoughtus' estimated weight. But two fossils is hardly enough to garner a conclusive estimate, especially since the Amphicoelias samples in question mysteriously vanished decades ago.

"There are a number of highly dubious but supposedly gigantic dinosaur taxa, such as Amphicoelias and Bruhathkayosaurus," the study's lead author Kenneth Lacovara told me. "Some websites list masses for these 'taxa,' but I would not consider those guesses to be 'calculated' or reliable."

Because these species are only known from only a few samples, it's difficult to estimate their size with a high degree of accuracy. Even if rough size estimates of other species eclipse Dreadnoughtus, the latter still remains the largest to be reliably measured—but not necessarily the largest ever.

"I think it is very likely that Argentinosaurus is the most massive dinosaur yet known," Lacovara told Discovery News. "However, I don't think we can make a reliable estimation of its mass."

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And that's the crux of what sets Dreadnoughtus apart from the remains of other titanosaurs. Because this specimen is by far the most complete titanosaur ever found, with over 45 percent of the original animal recovered intact, Lacovara's team was able to produce much more accurate estimates of its size.

Indeed, the team reconstructed about 70 percent of the animal's bone types using digital modeling. (That's excluding the head; the team was able to reconstruct about 45 percent of the total skeleton including the head.)

That's an abnormally detailed reconstruction for a massive sauropod, given that the group leaves behind notoriously piecemeal remains. For instance, the most well-preserved titanosaur discovered previous to Dreadnoughtus—Futalognkosaurus—is only 27 percent complete by bone type, excluding the head.

Dreadnoughtus says hi, tiny human. Image: Lacovara Lab

In addition to working with the most intact titanosaur ever discovered, the team was also stringent about its methodology. According to Lacovara, there are quite a few different methods for estimating a titanosaur's size, but you basically need to know the circumference of the animal's femur and humerus if you want an accurate prediction.

"I think it's fair to say that the humeral/femoral circumference method is the most widely accepted and only reliable means for calculating the mass of quadrupedal dinosaurs," he told me. "Attempting to estimate the size of one from the other necessitates making assumptions about body proportions."

"In our paper, we followed other authors by excluding taxa that are known from only the humerus or the femur, because calculating the circumference of one of these bones from the other adds another assumption and additional uncertainty," he added. "Thus we feel that we have taken the most conservative and reliable approach."

So while this doesn't mean Dreadnoughtus has necessarily won the coveted "biggest dinosaur ever" award, it is the largest that's been quantified in detail. It is also certainly the titanosaur that will reveal the most of any yet found about the morphology of the largest animals ever to roam on land. That is much more consequential than simply outweighing previous titanosaurs.

On top of that, Dreadnoughtus has one of the coolest names in dinosaur history (and that's a pretty cutthroat category). Why should carnivores hog all the glory? As Lacovara points out, herbivores like Drednoughtus were the true fearless badasses of the Mesozoic.

"With a body the size of a house, the weight of a herd of elephants, and a weaponized tail, Dreadnoughtus would have feared nothing," Lacovara said in a Drexel statement. "I think it's time the herbivores get their due for being the toughest creatures in an environment."

You only need to look at the battle-scarred bodies of meat-eaters like Sue or Big Al to grasp the truth of that statement. Even tyrannosaurs had to be careful of the dangers lurking around every corner, but nothing could take down Dreadnoughtus.