Ultrasaurus

This article is about the dubious dinosaur genus from South Korea. For the invalid dinosaur genus from Colorado, see Ultrasauros.

Ultrasaurus (meaning "ultra lizard"^[2]) is a genus of sauropod dinosaur discovered by Haang Mook Kim in South Korea. However, the name was first used unofficially (as a nomen nudum) in 1979 by Jim Jensen to describe a set of giant dinosaur bones he discovered in the United States. Because Kim published the name for his specimen before Jensen could do so officially, George Olshevsky renamed the specimen as Ultrasauros. Jensen's giant sauropod was later found to be a chimera, and the type remains are now assigned to Supersaurus.

Ultrasaurus Temporal range: Early Cretaceous, 110–100 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Clade:	†Sauropoda
Genus:	†Ultrasaurus Kim, 1983[1]
Species:	†U. tabriensis
Binomial name
†Ultrasaurus tabriensis Kim, 1983[1]
Synonyms
Hltrasurus Kim, 1994 (sic)

Mistaken assessments

A collection of bones discovered by Jim Jensen, of Brigham Young University, at the Dry Mesa Quarry, Colorado were originally believed to belong to the largest dinosaur ever. Jensen informally called this supposedly new dinosaur "Ultrasaurus", and this name was widely used by the press and in scientific literature as a nomen nudum (informal name lacking an actual scientific description).^[3]

In 1983, Haang Mook Kim published a paper describing a different specimen representing a new dinosaur species, which he named Ultrasaurus tabriensis, because he believed it was bigger than Supersaurus.^[1] However, Kim's assessment was incorrect; his dinosaur was much smaller than he believed, because he mistook a partial humerus for an ulna.^[4] Since Kim was the first to publish the name Ultrasaurus, the name officially applied to the South Korean sauropod, and could no longer be used as an official name for Jensen's giant specimen.^[3]

Jensen published a paper describing his original discovery in 1985,^[5] but since the name Ultrasaurus was already in use (or "preoccupied"), his discovery was renamed in 1991 to Ultrasauros by George Olshevsky.^[6] However, Jensen's discovery was a chimera, as the collection of fossils came from two different dinosaur genera Supersaurus and Brachiosaurus, both of which already had names. So the new name, Ultrasauros, is now considered as a junior synonym for the dinosaur officially known as Supersaurus.^[7]

Description

Ultrasaurus lived 100 to 110 million years ago, during the Aptian and Albian stages of the Early Cretaceous. It is known from the holotype DGBU-1973, which consists of part of the dinosaur's front leg or “hand” (humerus) initially mistaken as the upper (proximal) end of the right medial forearm (ulna), and DGBU-1978-A, a single tailbone (vertebrae) from the Gugyedong Formation, belonging to the Hayang Group.^[1][4]

Classification

Kim's Ultrasaurus is currently a nomen dubium. Not enough is known about the specimen to formally assign it to a specific family of sauropods.^[4]