Sunday, 8 February 2015

Creature 131: Amphicoelias fragillimus

The biggest dinosaur ever and we lost it!

Amphicoelias fragillimus is a very large dinosaur. Despite the fact that remains of this gargantuan beast are far from complete, we are fairly confident that it is the largest dinosaur we know about. By far.

Size of  Amphicoelias fragillimus compared to next biggest dinosaurs

It's estimated length is 58 m long and it's weight is estimated at 122 tonne. It was a big fella! These estimates are highly speculative as the species is known only from a single fossil of a part of an individual vertebra called a neural arch. However, this neural arch was 1.5 meters tall. The size estimate was made based of assumptions that this monster has roughly the same proportions as closely related species, an assumption which usually more or less holds true. The confidence that this is indeed the largest dinosaur we have discovered comes from the fact that the second largest,  Argentinosaurus huinculensis does not reach 40 m long at the most generous estimates. According to the field notes the tip of an enormous femur was also found just a few tens of meters away, which was probably from the same specimen, but we don't know much about that for reasons I will explain below.

This specimen was found with several other very large dinosaurs in the same deposit in the late 19th century.  You would think it is pretty hard to lose the largest dinosaur in the world, but somehow we did. That's right it's gone and hasn't been seen in over a century.  We have no idea what happened to it or who had it last. It's gone. We are working off drawings and descriptions done by the scientists who studied it at the time.

Reconstruction of the lost neural arch

The only fragments of this species to be found so far are from the Upper Jurrassic Morrison formation in Western United States.

Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Sauropoda
Genus: Amphicoelias
Species: Amphicoelias fragillimus

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