From Academic Kids


Conservation status: Fossil

Scientific classification

Template:Taxobox infraordo entry


S. vivianae

Ultrasauros (formerly Ultrasaurus) is an invalid sauropod genus, with a messy history. When the jumbled bones were discovered in 1979 at the Dry Mesa Dinosaur Quarry in Utah, it was hailed as the largest dinosaur ever. Unfortunately, the specimen is actually a chimera, composed of bones from a Supersaurus and a large Brachiosaurus.


Jumbled bones

The backbone (a dorsal vertebra, labeled BYU 9044) that was used to define the new species actually belongs to a Supersaurus. In fact, it probably belongs to the original Supersaurus, which was discovered in the same quarry in 1972. Other bones, like the shoulder girdle (scapulocoracoid, BYU 9462) belong to a Brachiosaurus, possibly a large specimen of Brachiosaurus altithorax. (Curtice, 1996)

The Brachiosaurus bones indicate a large, but not record-breaking individual, a little larger than the Giraffatitan brancai in the Humboldt Museum of Berlin, which was the largest known dinosaur for decades. Larger specimens of Brachiosaurus are known from the Tendaguru Beds of Tanzania, in east Africa.

Originally, the bones were believed to represent an single dinosaur that was about 25 to 30 meters (80 to 100 feet) long, 8 meters (25 feet) high at the shoulder, 15 meters (50 feet) in total height, and weighing maybe 70 metric tonnes (75 tons). At the time, mass estimates ranged up to 180 tons, which placed it in the same category as the blue whale and the equally problematic Bruhathkayosaurus. More current estimates are far more conservative.

What's in a name?

Even the naming is a mess. Ultrasaurus was the original choice, and was widely used by the media after the discovery in 1979. However, the name of a new species must be published to become official.

In 1983, Haang Mook Kim was the first to use the name formally, describing what he believed was a new Ultrasaurus from South Korea. Obviously, it was not the same animal. In fact, it was a much smaller dinosaur, because he mistook a humerus for a femur. But this did qualify as formal publication, so he accidentally defined the Ultrasaurus genus. The official Ultrasaurus is still regarded as a legitimate, if dubious genus.

So when James A. Jensen finally published a paper describing his find in 1985, he had to choose a new name (in technical terms, his original choice was "preoccupied"). In 1991, at his suggestion, George Olshevsky changed one letter, and renamed it Ultrasauros.

When it was discovered that the new name referred to bones from two separate, and already known species, the name Ultrasauros became a junior synonym for Supersaurus. To make matters even more complicated, it is speculated that Supersaurus is actually just a small Amphicoelias fragillimus, making it a junior synonym of the Amphicoelias genus, which was named by Edward Drinker Cope over a century ago — though without additional remains that is impossible to establish.

Since the bones from the Brachiosaurus were only used as a secondary reference for the new species, Ultrasauros is not a junior synonym for Brachiosaurus.


  • "Three new sauropod dinosaurs from the Upper Jurassic of Colorado", by James A. Jensen (1985). Great Basin Naturalist, issue 45, pages 697 to 709.
  • "A re-assessment of Ultrasauros macintoshi (Jensen, 1985)", by Brian Curtice, Ken Stadtman, and Linda Curtice (1996). The Continental Jurassic: Transactions of the Continental Jurassic Symposium, Museum of Northern Arizona Bulletin number 60, pages 87 to 95, edited by M. Morales.

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