Supersaurus, meaning “super lizard” is a genus of diplodocid sauropod dinosaur that was discovered by Vivian Jones of Delta, Colorado, in the Upper Jurassic Morrison Formation of Colorado in the year 1972. The fossil remains came from the Brushy Basin Member of the formation, dating back to about 153 million years ago. It’s among the largest dinosaurs known from good remains, possibly reaching 108 to 112 feet long and around 35 to 40 tons.
In most respects, Supersaurus is much like Apatosaurus in regards to anatomy, but it is less robustly built with particularly elongated cervical vertebrae, resulting into one of the longest known sauropod necks. Supersaurus is present in stratigraphic zone 5 of the Morrison, dating from the Tithonian.
Most studies of diplodocid relationships have found it to contain two primary subgroups: Diplodonicae, which contains those diplodocus more closely related to Apatosaurus than to Diplodocus. Initially, it was though that Supersaurus was related to the long-necked diplodocid Barosaurus, therefore, a member of the subfamily Diplodocinae, though most later studies found Supersaurus to be a close relative of the familiar Apatosaurus belonging to the group Apatosaurinae. However, some later studies cast some doubt on this paradigm. One comprehensive study of diplodocid relationships that were 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 increasingly more closely related to Diplodocus.
The original fossil remains of Supersaurus, discovered in the Dry Mesa Quarry, produced only a few bones: the shoulder girdle, a few neck vertebrae, and an ischium. This shoulder girdle stood some 8 feet tall if placed on its end.
A new and much more complete specimen of Supersaurus, nicknamed ‘Jimbo’, WDC DMJ-021, was found in Converse County, Wyoming in 1996. It’s currently being prepared and was described in the year 2007. The bones are being held at the Wyoming Dinosaur Center. By comparing the two specimens, it could be established that a series of tail vertebrae in reference to Supersaurus by Jensen may have belonged to some other form.
Paleontologist James A. Jensen, who described the initial Supersaurus specimen, simultaneously reported the discovery of another gigantic sauropod, which would later be named “Ultrasaurus” macintoshi which was later renamed Ultrasauros macintoshi. The type specimen of Ultrasauros, being a backbone, was later found to have come from Supersaurus. In fact, it most likely belonged to the initial Supersaurus specimen, which was discovered in the same quarry in 1972. Therefore, Ultrasauros became a junior objective synonym of Supersaurus, which has been named first and thus keeps hold of priority, and the name Ultrasauros was abandoned.
Other bones that were found at the same location and initially though to belong to Ultrasauros, like a shoulder girdle, actually belonged to Brachiosaurus, possibly a sizable specimen of Brachiosaurus altithorax. The Brachiosaurus bones specify a large, but not record-breaking individual, a little larger than the “Brachiosaurus” brancai mount in the Humboldt Museum in Berlin. Larger specimens of Brachiosaurus are known from the Tendaguru beds in Tanzania, in east Africa.
Originally, these Supersaurus and Brachiosaurus bones were believed to represent a single dinosaur that was estimated to reach about 80 to 10 feet long, 25 feet high at the shoulder, 50 feet in total height, and weighing around 75 short tons. At the time, mass estimates ranged up to 180 tons, which put it in the same category as the blue whale and the equally problematic Bruhathkayosaurus.
The naming of the chimeric Ultrasauros has a similarly complex history. Ultrasauros was the initial choice, and was widely used by the media after the discovery in the year 1979. However, the name of a new species must be in print with a new description to become official.
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 huge dinosaur in South Korea. This was a different, much smaller dinosaur than Jensen’s find, but Kim though it represented a similarly enormous animal because he confused a femur for a humerus. While the logic of naming was incorrect, the Ultrasaurus from Kim’s find fulfilled the requirements for naming and became regarded as a justifiable, if doubtful genus. Thus, due to Jensen not publishing his own Ultrasaurus find until 1985, Kim’s use retained its official priority of name, and Jensen was forced to choose a new name. In 1991, at his suggestion, George Olshevsky changed one letter, and renamed Jensen’s sauropod Ultrasauros.
When it was later discovered that the new name was in reference to bones from two separate and already known species, the name Ultrasauros became a junior synonym for Supersaurus. Since the bones from the Brachiosaurus were only used as a secondary reference for the new species, Ultrasauros isn’t a junior synonym for Brachiosaurus. Since Supersaurus was named slightly earlier, the name Ultrasauros has been unnecessary in favor of Supersaurus.
Another diplodocid dinosaur found near the original Supersaurus quarry, known from a backbone, was named Dystylosaurus edwini and is now also considered to be a specimen of Supersaurus vivianae. Hence, Dystylosaurus has become a junior synonym of Supersaurus as well.