Supersaurus (meaning "super lizard") is a genus of diplodocid sauropod dinosaur that lived in North America during the Late Jurassic period.

[10] A much more complete specimen WDC DMJ-021, was found in Converse County, Wyoming in 1986 by Brandon Flyr and Bart Lesco while out hiking and was reported to the people who owned the land at the time.

A comparison of WDC DMJ-021 and other specimens previously assigned to Supersaurus was done in order to help decide what material from the Dry Mesa Quarry belonged to the genus.

At the time, mass estimates ranged up to 180 tons,[14] which placed it in the same category as the blue whale and the equally problematic Bruhathkayosaurus.

[15] Before Jim Jensen published his discovery in 1985, another paleontologist, Kim Haang Mook, used the name Ultrasaurus in a 1983 publication to describe what he believed was a giant dinosaur in South Korea.

This was a different, much smaller dinosaur than Jensen's find, but Kim thought it represented a similarly gigantic animal because he confused a humerus for an ulna.

While the result obtained was 225 years, the study strongly states that a value this high is extremely unlikely and more reflects the limitations of the methodology in calculating the age of exceptionally old individuals.

In fact, the study suggests Jimbo was so old that its exact age cannot be reliably calculated by the applied methodology.

[5] Thus, despite the lack of a truly reliable age value, the Jimbo specimen of Supersaurus can be considered as possibly the oldest dinosaur known thus far.

[4] Michael Benton also agreed with the reclassification, giving the Supersaurus BYU 9024 specimen an approximate length of up to an impressive 50 metres (160 ft), which would have made it the longest animal to ever live.

[21] The assignment of the more complete specimen, WDC DMJ-021, to Supersaurus suggests that in most respects it was very similar in anatomy to Apatosaurus but less robustly built with especially elongated cervical vertebrae, resulting in one of the longest-known sauropod necks.

One comprehensive study of diplodocoid relationships published by Whitlock in 2011 found Apatosaurus itself to lie at the base of the diplodocid family tree, and other "apatosaurines", including Supersaurus, to be progressively more closely related to Diplodocus (making them diplodocines).