Biggest Dinosaur Ever? Maybe. Maybe Not.

Paleontologists working in Argentina have uncovered the bones of what may be the largest dinosaur ever. I want to stress the uncertainty in that opening sentence. Despite various news outlets already calling the contest, we don’t yet know which titanic dinosaur wins the superlative of “biggest creature ever to walk the Earth.”

Don’t misunderstand me – the new find is certainly worth getting excited about. Found by a farm worker in the vicinity of La Flecha, Argentina, and excavated by a crew from the Museo Paleontológico Egidio Feruglio, the 95 million year old site contains over 150 bones belonging to seven individuals of  the same long-necked, heavy-bodied species. Even better, the dinosaur might be new to science, and the presence of so many specimens in one spot could yield detailed insights into the growth, ecology, and behavior of the dinosaur.

But the dinosaur’s massive size is what has catapulted it into the headlines this weekend. Press photos show paleontologists posing for scale against a femur bigger than they are – a required photo-op for any researcher who works with such enormous bones – and an initial estimate from one such bone suggests that the new dinosaur was 130 feet long and weighed 77 tons. If accurate, this would make the titanosaur the top contender to the biggest dinosaur yet known. The trouble is that it’s too early to tell whether or not the estimates are on the mark.

A reconstruction of Supersaurus - in tan, against the wall - looms over the Jurassic Hall of the Museum of Ancient Life. Snapshot by  Brian Switek.
A reconstruction of Supersaurus – in tan, against the wall – looms over the Jurassic Hall of the Museum of Ancient Life. Snapshot by Brian Switek.

The tragedy of the biggest sauropods is that they’re so scrappy. Argentinosaurus – often cited as being about 100 feet long and in the range of 80 tons – is only known from a relatively paltry collection of vertebrae, ribs, and an incomplete femur. Bruhathkayosaurus, a dinosaur that may have been as big or even bigger than Argentinosaurus, was only known from limb, hip, and tail elements, and those fossils disappeared (much like the near-mythical dinosaur giant Amphicoelias, estimated to be 190 feet long from a long-lost piece of vertebra).

Even sauropods known from a decent amount of material are still too incompletely known to get a direct idea of how long and heavy they were. In order to estimate the size of dinosaurs such as Futalognkosaurus, Supersaurus, and “Seismosaurus“, paleontologists have to turn to more-complete skeletons of smaller, closely-related dinosaurs and scale up. This scrappy record is important to keep in mind because, among other parts, tails make a big difference in this ongoing “my dinosaur is bigger than yours” contest.

A great deal of a sauropod’s length was in the tail, and how long that tail really was hinges upon how many vertebrae were in that part of the spine. The trouble is that complete dinosaur tails are very rare in the fossil record, and some of those precious fossils even suggest that the number of vertebrae in a dinosaur species’ tail could slightly vary from one individual to the next. When you’re dealing with dinosaurs that had vertebrae measured in feet, not inches, the number of tail vertebrae paleontologists reconstruct can make a big difference for a size estimate. And given that the new bonebed contains only 150 bones between seven individuals, the length of the sauropod’s tail – and other parts – is going to have to rely on what we know about other species.

Weight is another matter altogether. Determining a dinosaur’s body mass not only relies on filling in missing bones based upon close relatives, but also a particular researcher’s perception of whether the dinosaur in question had a beefy build or was leaner. That’s why paleontologists are familiar with shrinking sauropods.

Paleontologist Jim Jensen with the reconstructed foot of the now-discarded "Ultrasauros." Photo by  Doctorjrj.
Paleontologist Jim Jensen with the reconstructed foot of the now-discarded “Ultrasauros.” Photo by Doctorjrj.

When I was a kid, the 90-foot-long, the 180 ton “Ultrasaurus” was supposed to be the biggest dinosaur ever. Then it turned out that this dinosaur was a composite of multiple individuals found in the same quarry, with some bones belonging to the substantial Supersaurus and others to a big, but not record-breaking, Brachiosaurus.

Supersaurus itself has fared a bit better, now estimated at 110 feet and about 45 tons, but the same isn’t true for another childhood favorite of mine. In news pieces and books, “Seismosaurus” was said to be 120-170 feet long and weigh over 100 tons. Today, the dinosaur has been recognized as a big species of DiplodocusD. hallorum – that was closer to 108 feet long and significantly less hefty than earlier estimates. And don’t even get me started on the titanosaur that was heralded in headlines as maybe being the largest of all time despite being known from a single tooth.

Dinosaurs aren’t the only animals to get downsized. The specimen of the giant marine reptile Pliosaurus nicknamed “Predator X” was initially said to be 50 feet long in documentaries and news items, supposedly the largest pliosaur of all time, but was later downsized to 33-42 feet long. Prehistoric creatures ballyhooed as “the biggest ever” upon discovery have a tendency to shrink by time of publication.

None of this is to say that the newly-discovered sauropod in Argentina is out of the running for the title of the largest dinosaur yet found. The sauropod could very well earn that distinction, or at least put in a good show against the other contenders both named and as-yet-unnamed. But there’s no way to say for sure just yet.

Size extrapolations from a single femur are not the final word, especially when there are pieces of comparably-sized dinosaurs out there. The new dinosaur will undoubtedly have lots of missing pieces that will have to be filled in and then used as a basis to estimate body mass, and I honestly wouldn’t be surprised if this turned out to be another roughly 110-foot-long sauropod with a weight about 50 tons. The fact that the best-known giant sauropods cluster in this range might hint that getting much bigger than that was biologically difficult – perhaps a marker of an upper limit for how big dinosaurs could be.

Then again, this new dinosaur could blow past that barrier and raise new questions about how these animals lived so large. We’ll have to wait for the published details and the ensuing scientific discussion. Ultimately, though, the best part of the discovery is that paleontologists have turned up many bones from multiple individuals, offering paleontologists a wealth of material to investigate how these ancient animals lived. Size isn’t everything.

28 thoughts on “Biggest Dinosaur Ever? Maybe. Maybe Not.

  1. Rather like judging the size and shape of a car after finding a single wheel and tire in the desert!

  2. Brian writes: “Size extrapolations from a single femur are not the final word…”

    I completely agree with this statement in general, particularly for large sauropods, which are larger than all living terrestrial tetrapods. These living forms are our best data for deriving the scaling relationships of limb bones to mass upon which non-avian dinosaur size estimates are based, yet there are always dangers in extrapolating beyond the range of values of your original sample. Still, if the MEF researchers were using the allometric equations of Campione & Evans (2012), the estimates are probably pretty good, as those authors found a very strong relationship between femoral dimensions and mass across all orders of magnitude. Even if these new equations were used, I wonder if the reported difference in estimated size between the new find and Argentinosaurus (77 vs 70 metric tons) is significant when you include the uncertainty derived from 95% confidence intervals.

    Campione, N.E., and D.C. Evans. 2012. A universal scaling relationship between body mass and proximal limb bone dimensions in quadrupedal terrestrial tetrapods. BMC Biology 10:60, 1-21. DOI: 10.1186/1741-7007-10-60

  3. Is there any way of estimating how big one of these “gigantasours” was at birth/hatching and how long it would take for them to grow to the size estimated?

  4. The best method to estimate age for most animals is to biopsy their bones and look at the tissue. Most vertebrates have yearly growth rings in their bones, similar to the rings in a tree. One complication is that sauropods (atypically for dinosaurs) remodel and repair their bones starting from a young age. Without a complete set of sizes from baby to adult, it’s hard to gauge exactly how many years it took. However, most dinosaurs reached full size in fewer than 25 or 30 years.

    Sauropod babies were not huge at hatching – the largest sauropod eggs known are only 6-8″ in diameter (only!). This is a little bigger than an ostrich egg, but smaller than an elephant bird egg.

  5. Via Occam’s Razor, something tells me the remains announced by the press is much more probably the first reasonably complete remnants of Argentinosaurus huinculensis. The location of the remains and the age of the horizon that hosts the bonebed are from more-or-less the same provenance and estimated temporal range for Argentinosaurus huinculensis (although admittedly, the use of Occam’s Razor is prone to the fallacy of oversimplification)

  6. There seems to be quite a lot of this beastie, by the standards of most sauropods. Is there enough that it can be confidently assigned to a new taxon on morphological grounds, rather than being a specimen of Argentinosaurus that happens to be bigger than the type specimen? After all size variation in Argentinosaurus is unknown, almost by definition.

  7. One quick detail, Brian.

    It turns out that the brachiosaur remains referred to “Ultrasauros” are actually a unique species separate from Brachiosaurus itself. The famous shoulder blade is fused to its coracoid, indicating the animal was an adult. But the coracoid is shaped differently and a good bit smaller than that of the Brachiosaurus holotype, which is not fused to anything – indicating the holotype was a teenager at the time of death.

    So adult “Ultrasauros” is actually smaller (or at least thinner-chested) than a teenage Brachiosaurus.

  8. Just imagine for a second that if any of these animals had to be weaned by the mother, Which I know would be unlikely, but the amount of “Milk” That would be necessary for it to survive would be enormous!!!
    And if they were hatched how strong those eggs would have to be!!
    It certainly makes you think twice!

  9. Amphicoelias sketches is based on over 100 years of lost fossils some assumptions, it is as real as Red Riding Hood. Until there are tangible evidence, Argentina has the largest sauropods.

  10. In all the excitement about the size, I wonder if a rather large (sorry) mystery isn’t being overlooked — why were SEVEN such extremely large animals so close together, and what was it that killed them and buried them all at the same time?

  11. @ chris y:

    I fully agree with your position that the fossils in the bonebed are the remnants of larger (and presumably) older Argentinosaurus. After all, it’s indeed very possible that the Argentinosaurus holotype is a subadult to a young adult while the largest individuals in the bonebed are likely to be old adults.

  12. I’ve yet to see a measurement given for any of the bones. Seriously, did no one there have a tape measure?

  13. Dwayne LaGrou, it would be impossible to even consider that, being the fact that these are dinosaurs and they do not produce milk. Only mammals produce milk for their young and last time I checked Dinosaurs weren’t mammals.

  14. There were other potentially larger taxa in Australia. Individual early Cretaceous sauropod tracks in track-ways north of Broome, Western Australia, are 1.75 meters (5′ 9″) wide. When first analysed by ichnologist Tony Thulborn, it was argued that this would make the track-maker the largest dinosaur known from any continent. Sadly, so far only the tracks are known but increasingly impressive dinosaur skeletons are being found each year in central Queensland so one day, perhaps…

  15. yes, it’ll be interesting to see what the final size estimate is. i’m curious to know how much fodder such an herbivore needs. it surely had an enormous gut to digest a hugh amount of food. what are the current ideas about its metabolism? also i can’t help but wonder at the living environments and ecosystems the surface of these guys provided. how many species that remain unknown to science made their homes exclusivly on the surface of an Argentinosaurus?

    1. Excellent, thought-provoking thoughts, Ian! I also wonder about other aspects of the environment that would support these things, besides the abundant food — wouldn’t they require large, open areas with fairly smooth and level plains?

  16. Brian, I’m not a scientist, I´m a communicator and graphic designer -so I apologize for technical mitakes-. I live in Trelew (the city that houses the MEF – Paleontological Museum Egidio Feruglio), where we are so excited about this discovery!!
    But celebration held at the museum , was not just for the record size of the fossils found , but (and on the whole thing ) the quantity of fossil remains of this specimen, and the unique degree of preservation.
    I understand –and share- your questions about it, but I think it´s also a logical process of science! We all know that the latest discovery is the truth, until disprove. In the same museum, in the center of the Cretaceous hall of the exhibition, is a group of Titanosaurus , some of them discovered in 1938. At the time, it was named for its titanic size and today… well, they seem to be the rests of a “dinosaur´s pet shop”.
    Another issue to consider, is that the photo that circulated around the world, is an informal picture taken at the museum months ago, it was not intended to became famous. Why? For one reason: the paleontologist who poses next to the fossil, is 5,2 ft tall!
    That’s the beauty of science, I think. Everything is the very true, until proven otherwise. But for now, and based on the wonder that we could appreciate at the site where it was found, this dinosaur is the largest, most complete and best preserved ever seen in Patagonia.

  17. It’s very fascinating that one can reconstruct an entire animal from a single bone or tooth. In the case of the Megolodon. I do feel with proper calculations and previous scientific findings, one could come up with a significantly close approximate size.
    With all the technology that we now have to help in calculating and reconstructing skeletal stuctures, I find it plausible to get a
    “Ball park” idea of size. So very exciting!
    I’ve been a herpticulturist since I was a young boy and have always been intrigued
    and fascinated with paleontology and also geology. It’s awesome and really gets you thinking.I love this stuff!

  18. “In news pieces and books, “Seismosaurus” was said to be 120-170 feet long and weigh over 100 tons. Today, the dinosaur has been recognized as a big species of Diplodocus – D. hallorum – that was closer to 108 feet long and significantly less hefty than earlier estimates.”

    To be fair, it’s recently been stated that “the likes of Argentinosaurus and Seismosaurus” reached “40 meters from the tip of the snout to the tip of the tail” (See the 2nd edition of “Dinosaurs: A Concise Natural History”).

  19. Does size really matter? Many people are using different parameters, and, most crucially, not all parameters have been used.

  20. I think we need to wait until we have all the information. Everyone is basing their opinions off of this one article. How could we base the size off of a few bones? If that is there way of defining size, what would have happened if we only found the radius and ulna of the T-Rex? The T-Rex would be a tiny skeleton in museums. I am not holding my breath that this indeed will be the biggest dinosaur.

  21. As the reconstructor, and so champion of Argentinosaurus, I have my preference. But the matter is not so complicated. The confusion begins with biggest – which means most massive, i.e. heaviest, not longest. The 10 to 15 percent of Argentinosaurus known is actually a lot by the standards of most dinosaur finds. Certainly with its tibia and dorsal vertebrae, enough to compare with similar elements on other sauropods. None bigger is known.
    As for longest, that is more speculative, given the incomplete nature of finds. Sauropod length appears to be inversely proportionate to the size of the person who found it. So the vertically-challenged David Gillette made Seismosaurus grow like Pinocchio’s nose anytime anyone found anything said to be nearly as long.
    Paul Sereno wanted so badly that his Carcharodontosaurus skull represent the largest theropod, as he told the NY Times, that he grossly exaggerated its snout, in the absence of a pre-maxillary bone, into the Jimmy Durante of dinosaurs. Subsequent finds of the actual largest (not longest) theropod, its more massive relative Giganotosaurus (ahem, one I reconstructed) which had a pre-max, unmasked Sereno’s Pinocchiosaurus.
    All these “biggest” claims are shorthand for “pay attention to my animal!” They are all, to use scientific language, “wicked cool,” and deserve our attention. And there will always be a bigger one out there.

  22. Was this bone bed a life assemblage or a death assemblage? Did these animals die in place suddenly being buried where they fell as in a volcanic eruption, or did they die many miles away by drowning in a raging river, their remains ending up here? Further clues to the exact nature of this group may lie in the surrounding region. There may be a trail of wreckage leading to this bed, as when a plane crashes in the desert, its parts being flung far and wide. Does a method exist that could determine the true origin of this bone bed in time and place, or is trying to pin point the exact location of an event that happened so long ago unrealistic? Everyone would like to be remembered as the discoverer of the world’s largest dinosaur. This is only human. Perhaps a more thorough investigation of the surrounding region may lead to further clues as to the true nature of this beastie? Just a thought. Great find, though!

  23. In 1992 They discovered Seismosaurus That was thé longent found at thé time. 150 fêet long. Titosaures Is much bigger.??

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