What is Amphicoelias Fragillimus?

Michael Anissimov
Michael Anissimov

Amphicoelias fragillimus was a sauropod herbivore dinosaur, possibly the largest dinosaur (or animal of any kind) that ever existed. Its veracity is contested because the only bones of the dinosaur, a partial vertebra and a gigantic femur, have since been lost. The vertebra fragment, located by an employee of the American paleontologist Edward Cope in 1877, measured 1.5 m (5 ft) in length. The vertebra it was a part of during the life of the dinosaur would have been 2.7 m (8.8 ft) in length. Extrapolating the length of the vertebra to the total size of the dinosaur, based on similar species, has given an estimated length of 40-60 m (131-196 ft), with a mass of up to 122 tonnes (135 tons), longer than a blue whale but approximately two-thirds its weight.

Woman holding a book
Woman holding a book

Amphicoelias, which means "doubly-hollow" is a reference to the animal's thin vertebral walls, which would have been necessary to allow an animal of that size to carry its own skeleton. The second part of the species name, fragillimus, is a reference to the fragility of the fossil. It was discovered in Colorado mudstone, a weak rock that has the tendency to fragment into small, irregular cubes. A sketch of the fossil was only completed from one angle, which is unusual given Edward Cope's reputation for detail and drawings from multiple angles of every important fossil. Historians reason that this may have been because the fossil fragmented into pieces after the first sketch.

Amphicoelias was a diplodocid dinosaur, a family of sauropods known for their extremely long and slender bodies. Like other sauropods, an adult Amphicoelias probably would have had little need to worry about predators, spending all its time grazing foliage at the same height as its head, which would have been about 9 m (30 ft) off the ground. It is uncertain how old the dinosaur would have been at death or how fast it grew: it depends on its metabolism. If it were warm-blooded like mammals, it would have grown to full size in about 10 years, growing an average of roughly 20 ft/year, 1.7 ft per month, or a few inches per day. If it were cold-blooded like reptiles, it would have required a full century to reach the size at which it died. Scientists continue to debate whether dinosaurs in general were cold or warm-blooded, and the consensus seems to be that they were somewhere in between.

Unfortunately, all reports of Amphicoelias after the 1870s indicate that the bones in question had gone missing. Thus, there is considerable controversy whenever the dinosaur is presented as possibly being one of the largest creatures ever to have lived.

Michael Anissimov
Michael Anissimov

Michael is a longtime wiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Discussion Comments


@pastanaga - I was completely shocked when I found out how competitive and ruthless fossil collectors can be, so it wouldn't surprise me if this one did turn out to be some kind of fake.

There have been all kinds of cases of people pretending to have found something new and then either losing the evidence, or just cobbling it together from existing fossils.

And there would be a lot of prestige attached to finding the largest land animal that ever existed.


@fa5t3r - Well, yes and no. I mean, it's true that it's highly improbable that we'll ever be able to fill in all of the creatures that belong on Earth's family tree. But these creatures generally have a lot in common so we can still tell quite a bit from what we do find.

Since they found a couple of bones in this case, they'd be able to compare those to other fossils and see where they are the same and where they differ. Just like, if you found a horse tooth today, you'd be able to tell quite a bit about it by comparing it to the teeth of other herbivores and contrasting it with carnivores.

There are millions of unique species, but all those species are related, so it's not like scientists are starting from scratch every single time they find something new.

The only real problem is when something like this becomes controversial and they can't trust the evidence that is available.


This sort of thing always reminds me how little we actually know about the deep past and how much we may never know. If this particular kind of dinosaur was prone to produce fragile fossils, perhaps we'll never find decent examples of what it looked like. And there might have been other creatures back then that either don't produce fossils, or that we've simply never found. When you think about the enormous time span, the number of potential species (I mean, we don't even know all the species alive on Earth today) and the hurdles in fossils being made and being discovered, it's amazing that we ever find more than one example of any fossil type.

Paleontology is all about taking shots in the dark and speculating based on very little information.

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