Supersaurus

Supersaurus (meaning "super lizard") is a genus of diplodocid sauropod dinosaur discovered by Vivian Jones of Delta, Colorado, in the Upper Jurassic Morrison Formation of Colorado in 1972. The fossil remains came from the Brushy Basin Member of the formation, dating to about 153 million years ago.[1] It is among the largest dinosaurs known from good remains, possibly reaching 33 to 34 meters (108 to 112 ft) in length, and a weight of 35 to 40 tons.[2]

In most respects, Supersaurus is very similar in anatomy to Apatosaurus, but it is less robustly built with especially elongated cervical vertebrae, resulting in one of the longest known sauropod necks.[2] Supersaurus is present in stratigraphic zone 5 of the Morrison, dating from the Tithonian.

Classification
Most studies of diplodocid relationships have found it to contain two primary subgroups: Diplodocinae (containing those diplodocids more closely related to Diplodocus than to Apatosaurus) and Apatosaurinae (diplodocids more closely related to Apatosaurus than to Diplodocus). Originally, it was thought that Supersaurus was related to the long-necked diplodocid Barosaurus, and therefore a member of the subfamily Diplodocinae, though most later studies found Supersaurus to be a close relative of the familiar Apatosaurus in the group Apatosaurinae.[2] However, some later studies cast doubt on this paradigm. 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).

History
The original fossil remains of Supersaurus, discovered in the Dry Mesa Quarry, yielded only a few bones: the shoulder girdle (type specimen BYU 12962, earlier BYU 5500), an ischium (BYU 12946) and a few neck vertebrae. This shoulder girdle (or scapulocoracoid) stood some 2.4 meters (8 ft) tall, if placed on end.

A new and much more complete specimen of Supersaurus, nicknamed 'Jimbo', WDC DMJ-021, was found in Converse County, Wyoming in 1996. It is currently being prepared and was described in 2007. Its bones are being held at the Wyoming Dinosaur Center. By comparing the two specimens, it could be established that a series of tail vertebrae referred to Supersaurus by Jensen may have belonged to some other form.

Ultrasauros
Paleontologist James A. Jensen, who described the original Supersaurus specimen, simultaneously reported the discovery of another gigantic sauropod, which would later be named "Ultrasaurus" macintoshi[5] (later renamed Ultrasauros macintoshi). The type specimen (the specimen used to define a new species) of Ultrasauros, being a backbone (dorsal vertebra, labelled BYU 9044), was later found to have come from Supersaurus. In fact, it probably belonged to the original Supersaurus specimen, which was discovered in the same quarry in 1972. Therefore, Ultrasauros became a junior objective synonym of Supersaurus, which had been named first and thus retains priority, and the name Ultrasauros was abandoned.

Other bones that were found at the same location and originally thought to belong to Ultrasauros, like a shoulder girdle (scapulocoracoid, BYU 9462), actually belonged to Brachiosaurus, possibly a large specimen of Brachiosaurus altithorax.[6] The Brachiosaurus bones indicate a large, but not record-breaking individual, a little larger than the "Brachiosaurus" brancai (Giraffatitan brancai) mount in the Humboldt Museum of Berlin. Larger specimens of Brachiosaurus are known from the Tendaguru beds of Tanzania, in east Africa.

Originally, these Supersaurus and Brachiosaurus bones were believed to represent a single dinosaur that was estimated to reach about 25 to 30 meters (80 to 100 ft) long, 8 meters (25 ft) high at the shoulder, 15 meters (50 ft) in total height, and weighing maybe 70 metric tons (75 short tons). At the time, mass estimates ranged up to 180 tons,[7] which placed it in the same category as the blue whale and the equally problematic Bruhathkayosaurus.

Naming of Ultrasauros
The naming of the chimeric Ultrasauros has a similarly complicated history. 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 with a 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 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 femur (leg bone) for a humerus (arm bone). While the logic of naming was incorrect, the Ultrasaurus from Kim's find fulfilled the requirements for naming and became regarded as a legitimate, if dubious genus. Thus, because Jensen did not publish 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 technical terms, his original choice was "preoccupied" by Kim's sauropod). 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 referred 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 is not a junior synonym for Brachiosaurus. Since Supersaurus was named slightly earlier, the name Ultrasauros has been discarded in favor of Supersaurus.

Additional synonyms
Another diplodocid dinosaur found near the original Supersaurus quarry, known from a backbone (dorsal vertebra type specimen BYU 5750), was named Dystylosaurus edwini and is now also considered to be a specimen of Supersaurus vivianae. Hence, Dystylosaurus has also become a junior synonym of Supersaurus.