Smithsonian.com

A graphic comparing the largest sauropods. The red giant in the back represents the estimated size of Amphicoelias (the blue speck to the lower left is a human for scale). By DinoGuy2, from Wikipedia.

My friend and fellow science writer Ed Yong recently met the biggest mammal of all time. During a trip to Sri Lanka, Ed was able to get quite close to some blue whales—the most massive animals on earth. But are they the largest animals ever? When I tweeted Ed’s story, noting that he met the most immense mammal that has ever lived, Ed picked up that I specified the blue whale as the largest mammal ever, rather than the largest animal. “Are you hedging your bets for a sauropod?” he asked. Well, yes and no.

As sauropod expert Matt Wedel once pointed out, there are two “semi-apocryphal” dinosaurs that may have been significantly larger than the biggest whales. One of these is a legend among paleontologists. In 1878, paleontologist Edward Drinker Cope named the 150-million-year-old dinosaur Amphicoelias fragillimus on the basis of a huge but partial piece of a vertebra called a neural spine. By itself, this fragment reportedly measured almost five feet high. The dinosaur it belonged to must have been absolutely gigantic. We may never know. The bone was lost, and efforts to locate additional bones of the dinosaur have failed. From the description of the single scrap, paleontologist Ken Carpenter estimated that the dinosaur may have been 190 feet long. This would make Amphicoelias about twice as long as the longest known sauropods, but without additional fossils from this titan, estimating Amphicoelias‘ size requires speculation.

But there’s another dinosaur that may have outstripped whales. Or maybe not. Bruhathkayosaurus, a more recent contender for largest dinosaur, also has a tortured history. The dinosaur was named in 1989 on the basis of limb, hip and backbone elements found in the 70-million-year-old strata of India. At first, the remains seemed to represent one of the biggest predatory dinosaurs of all time, but paleontologists later recognized that the bones had come from a sauropod. These bones might indicate a dinosaur even larger than the roughly 100 foot long Argentinosaurus—the creature often cited as being the current record-holder for the biggest dinosaur of all time.

Despite being discovered just a few decades ago, however, the size and characteristics of Bruhathkayosaurus are almost as mysterious as those of Amphicoelias. The original description represents all that is known about this dinosaur, and as far as I am aware, no one has formally published a reexamination of the dinosaur’s skeleton. Informal estimates have placed this dinosaur at between 90 and 145 feet long, with weight estimates varying as well.

For the moment, the biggest confirmed dinosaurs all seem to fall around the same upper limit: around 100 feet long. Whether any species grew considerably bigger than this remains to be seen. The fact that so many dinosaurs seem to fall around this length might indicate that it represented the rough upper boundary for sauropod size, yet huge sauropods are so rare that it is difficult to say whether this is real or a factor of sampling and estimation techniques.

So are blue whales the biggest animals ever? In terms of mass, almost certainly yes. The biggest whales weigh more than 200 tons, and as Matt Wedel pointed out in his post on this mammal vs. dinosaur competition, even fairly liberal mass estimates for the biggest dinosaurs don’t come close to this. But dinosaurs may have whales beat when it comes to length. Supersaurus—one of the many confirmed giants—might have been a little longer than the 110 foot benchmark set by whales, and perhaps Amphicoelias was even longer. If only someone could find a good skeleton of such a giant.