Ultrasaurus

:"This article is about Ultrasaurus, a dubious dinosaur from South Korea. The article on the invalid giant dinosaur genus from Utah, in the United States, is at Supersaurus. For the fictional Zoid based on this dinosaur, see Ultrasaurus (Zoids)."Taxobox
name = "Ultrasaurus"
fossil_range = Early Cretaceous

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image_width = 200px
image_caption = Hypothetical life restoration of "Ultrasaurus", based on brachiosaurids.
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
infraordo = Sauropoda
genus = "Ultrasaurus"
genus_authority = Kim, 1983
subdivision_ranks = Species
subdivision =
*"U. tabriensis" Kim, 1983 (type)

"Ultrasaurus" 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, Jensen renamed his specimen "Ultrasauros". Jensen's giant sauropod was later found to be a chimera, and the type remains are now assigned to "Supersaurus".

Mistaken assessments

A collection of bones discovered by Jim Jensen, of Brigham Young University, at the Dry Mesa Quarry, Utah 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).

In 1983, Haang Mook Kim published a paper describing a different specimen representing a new dinosaur genus, which he named "Ultrasaurus tabriensis", because he believed it was an equally giant relative of Jensen's dinosaur. However, Kim's assessment was incorrect. His dinosaur was much smaller than he believed, because he mistook a leg bone ("femur") for an arm bone ("humerus"). However, since Kim was the first to publish the name "Ultrasaurus", the name officially applied to the small South Korean sauropod, and could no longer be used as an official name for Jensen's giant specimen.

Jensen published a paper describing his original discovery in 1985, but since the name "Ultrasaurus" was already in use (or "preoccupied"), his discovery was renamed in 1991 to "Ultrasaur"o"s". However, Jensen also made a mistake. His discovery was a chimera; the collection of fossils came from two different dinosaur species, both of which already had names. So his new name, "Ultrasaur"o"s", is now just an alternate name ("junior synonym") for the dinosaur officially known as "Supersaurus".

Kim's "Ultrasaurus" is currently "nomen dubium". Not enough is known about the specimen to formally assign it to a specific family of sauropods. It may even be a member of a known genus or species, which would make the name "Ultrasaurus" a junior synonym as well.

Description

"Ultrasaurus" lived 100 to 110 million years ago, during the Aptian and Albian stages of the early Cretaceous. It is known from part of an upper forearm (humerus), and some back bones (vertebrae).Kim, H.M. (1983). "Cretaceous dinosaurs from South Korea." "Journal of the Geological Society of Korea", 19(3): 115-126.]

References